ImmunologyA Brief Overview (Part 1)
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This series of articles comes with an English-Brazilian
Portuguese downloadable glossary of terms used
in immunology with the English terms explained (in
English) and translated into Portuguese. You can download
In its classical meaning, immunology is the study of
immunity, the processes by which organisms defend themselves
against infection. When this science took root about
one century ago, it attracted wide attention among the
biomedical community because of the promise it offered
for relief from epidemic infectious diseases. More recently,
immune responses became recognized as also being important
in processes which have to do with recognition phenomena,
self-characterization, growth and development, heredity,
aging, cancer, transplantation, thus being a fundamental
part of almost all human medical and veterinary specialties.
Immunological methods and reagents are applied to the
diagnosis, prevention and therapy of many diseases and
provide tools and concepts for probing mechanisms of
The virtually exponential growth of
this science is generally ascribed to the development
of relatively new techniques such as: immunofluorescence,
radioimmunoassay, electronic and scanning microscopy,
production of monoclonal antibodies, and genetic engineering
Many biological fields (such as genetics,
biochemistry, molecular biology, endocrinology, pharmacology,
histology, parasitology and virology, among others)
are strongly linked to Immunology. Also, the multiple
sources of interest have led to separating Immunology
into sub-specialties, such as: immunity to infectious
diseases, serology, immunochemistry, allergy, immunogenetics,
cellular immunology, neuroimmunology, immunopharmacology,
tumor immunology, transplantation immunity, immunodeficiency
diseases, immunotherapy, etc.
Immunology has its roots in the defense
against infectious disease, followed by the development
of vaccines, organ transplantation, immune responses
to malignancy, and a variety of immunotherapies. Modern
research in immunology draws on recent advances in cellular
and molecular biology, protein chemistry, and virology
to determine how the components of the immune system
function. In turn, the study of cells of the immune
system has contributed to our understanding of protein
structure, eucaryotic gene organization and regulation,
and intracellular protein transport and assembly. With
this expansion, immunology has grown beyond its original
meaning, and according to some scientists, immunobiology
has become a preferable term for this expanding field.
The development of this science can
be appraised by the huge volume of articles on this
subject: there are more than 900 journals that publish
more than 8000 articles per year on Immunology and many
prizes for Physiology and Medicine were awarded
to studies on Immunology and related sciences, including
the last one, in 1997! The current flood of literature
on Immunology and on sciences that apply immunological
tools and/or concepts, and the huge number of publications
that use this terminology, made me construct a glossary
for translators who are often stuck when they find immunological
jargon either in scientific/medical texts or in
material for the layperson.
The glossary that can be downloaded
from this page is far from complete, and it is almost
impossible to construct an exhaustive and updated glossary
in this endlessly changing subject.
ImmunologyA Brief Overview
By Lucia Mary Singer, Ph.D.
What is Immunity?
Historically the term immunity has meant protection
against disease and more specifically, infectious diseases.
The various cells and proteins responsible for immunity
constitute the immune system, and their collective
and orchestrated response to the introduction of foreign
substances (also called non-self substances)
is the immune response. Nowadays, we know that
the same basic mechanisms of resistance to infections
are also involved in the individuals response
to non-infectious foreign substances. Thus, when an
individual has a primary contact with a molecule or
cell, the immune system will first discriminate if this
is a self or a non-self agent.
Under normal conditions, if this substance/cell is the
same found in the organism, the immune system will not
react and we say that the individual is tolerant
to that agent. However, if the agent is recognized as
a non-self substance/cell it will trigger
a specific immune response, in addition to a non-specific
one, in an attempt to destroy it. These foreign substances
that elicit a specific immune response and react with
the product of this response are generically called
antigens. The mechanisms that normally protect
individuals from infections and eliminate foreign substances
are themselves capable of causing tissue injury and
disease (e.g., auto-immune diseases, rejection of grafts,
allergies) in some situations. Thus, Immunology deals
with understanding how the body distinguishes between
self and non-self molecules;
the remainder is technical detail...
Innate and Acquired Immunity
Vertebrates present two main types of immunity: innate
(also known as natural immunity) and acquired
or adaptive immunity.
Innate immunity encompasses the cells
and molecules with which an individual is born and it
is potentially ever-present, available on short notice
and non-specific; also, innate immunity is the first
line of defense against foreign cells or substances.
The innate immune system provides an immediate, non-lasting
resistance which is not improved by repeated infection.
Acquired immunity, on the other hand,
is specific to the foreign molecule or cell, thus being
an adaptive response to a given non-self
substance and also presents memory (i.e., the immune
system remembers a previous encounter with
a foreign microbe or molecule, so that subsequent encounters
increasingly stimulate defense mechanisms). The immunological
memory is the basis of the protective vaccination against
infectious diseases. For example, infection or vaccination
against smallpox, diphtheria or pertussis produce a
persistent immunity following infection or vaccination
and the development of memory lymphocytes,
which in turn will induce a more effective, long-lasting
and stronger immune response after a subsequent infection
The innate and specific immune systems
consist of a variety of molecules, cells and tissues.
The most important cells are the leukocytes
which fall into two broad categories: phagocytes (including
macrophages and neutrophyls) and natural killer cells,
which belong to the innate immune system, and lymphocytes
(specially T lymphocytes), which mediate the adaptive
The most important soluble factors
that mediate the innate immune response are: lysozyme,
a complex of substances generically called the complement
system and the so called acute-phase proteins (e.g.,
interferons and C-reactive protein). The main soluble
proteins responsible for the acquired immune response
are the antibodies.
If the first innate defenses are breached,
the specific immune mechanisms are activated and produce
a specific reaction to each infectious agent in an attempt
to erradicate that agent. Also the specific immune response
amplifies the protective mechanisms of natural immunity,
thus reinforcing the bodys ability to eliminate
the antigenic molecules.
Most infectious agents encountered by an individual
are prevented from entering the body surface by a variety
of physical and biochemical barriers, such as the intact
skin, mucus, cilia lining the trachea, acidity of the
stomach, lysozyme (a protein present in saliva and most
secretions which is able to split a bond of some bacterial
cell walls) and commensal organisms in the vagina and
If an infectious agent penetrates
an epithelial surface, it will meet a second set of
barriers: the phagocytes and the natural killer (NK)
cells. Phagocytes are able to engulf particles, including
many bacteria and fungi species, and destroy them, a
process called phagocytosis. The main phagocytic cells
are the neutrophyls, the monocytes and the macrophages.
NK cells are also leukocytes, which are able to recognize
cell surface changes that occur in tumoral cells and
in virus infected cells. NK cells are then able to bind
to those altered cells and kill them. This type of reaction
in which a lymphocyte kills a target cell is called
In addition to the phagocytic and
NK cells, soluble substances also operate in a coordinated
way, to erradicate the infectious agents. These include
some molecules referred to as acute-phase proteins,
the complement system proteins and interferons, which
increase rapidly in numbers during infections.
Acute phase proteins encompass the
C-reactive protein, a protein that can bind to pneumococci
and other bacteria and promote the activation of some
The complement system is a complex
of more than twenty serum proteins, whose overall functions
are to facilitate phagocytosis by binding to the antigens
(a process called opsonization), to control inflammation
and to destroy foreign agents through lysis of these
cells. The complement proteins interact with each other
and with other elements of the innate and specific immune
Interferons (IFNs) are a group of
proteins that are important in viral infections. Interferon
a and b are produced by cells infected by virus and
they act on other cells to induce a state of resistance
to viral infection. Another IFN, known as IFN-g, is
produced during the specific acquired immunity response
When an individual is exposed to a foreign antigen,
two basic types of effector mechanisms are normally
stimulated. One is mediated by specific molecules, called
antibodies. Antibodies are present in the blood and
various biological fluids and the antibody-mediated
immunity is called humoral immunity. The other
type of immune response is effected by cells, mainly
by the so called T lymphocytes, and confers a cell-mediated
Most immune responses involve the
activity and interplay of both the humoral and the cell-mediated
immune branches of the immune system. Furthermore, the
innate and the adaptive immune systems do not act in
a totally independent way. The following examples illustrate
this: antibodies opsonize infectious agents so that
phagocytes recognize and engulf their targets more effectively;
activated T lymphocytes produce certain hormones called
cytokines and some of these cytokines stimulate
phagocytes to destroy infectious agents in a more efficient
way; T lymphocytes help the so called B lymphocytes
to produce antibodies.
So, the immune system operates as
an orchestra in which all musical instruments are important,
although in some parts there are some solos, and the
conductor is the foreign agent which many times determines
which (if any) kind of response(s) will be elicited.
In the next installment of this series
we will approach the cells and molecules involved in
immunity, how they operate and we will have some words
about the deleterious effects that may result from the
activation of the immune system.
ImmunologyA Brief Overview
By Lucia Mary Singer, Ph.D.
Cells Involved in Immunity
In Part 1 and Part 2 of this series we presented an
overview about immunology, its importance and relationship
with other areas of the biomedical sciences, and approached
topics such as the self and non-self
recognition, innate and acquired immunity, stressing
how the immune system operates in an orchestrated way,
leading to an effective immune response. We also learned
that there are two basic forms of specific immunity:
humoral immunity, basically mediated by antibodies,
and cell-mediated immunity in which the responding lymphocytes
are the T lymphocytes.
The antibodies which mediate the specific
humoral immune response are produced by plasma cells.
Plasma cells are cells that evolve from activated
B lymphocytes which in turn become activated after
interaction with antigens. Plasma cells secrete antibodies
that eliminate extracellular microorganisms (that usually
do not live inside a cell, such as the pneumococci).
In cell-mediated immune responses, another set of lymphocytes,
the T lymphocytes, activate macrophages to kill intracellular
microbes and/or activate some types of T lymphocytes
(called cytotoxic T lymphocytes) to destroy infected
cells (such as virus-infected cells) as well as cells
bearing new antigens on their surfaces (e.g. malignant
Thus, several cell types are involved
in the specific immunity and the three major cell types
- Antigen presenting cells (APC): cells that process
antigens and present them to specific T and/or B cell
- B cellslymphocytes that mature in the Bone
- T cellslymphocytes that mature in the Thymus.
T and B lymphocytes are antigen-specific (they present
receptors that can react specifically with the antigen
that originated their development), whereas APCs do
not display specific receptors for the antigens with
which they are interacting.
Antigen presenting cells
(APCs)are a group of cells that do not
display antigen-specific receptors, and their main function
is processing and presenting antigens to T cell receptors.
The most important APCs are the macrophages. Macrophages
are long-lived phagocytes, strategically located in
different tissues (e.g., Langerhans cells in the skin,
Kupffer cells in the liver, microglial cells in the
brain), where they can encounter the antigens. They
play an important role both in antigen presentation
and later, in the course of the immune response, as
effector cells in cell-mediated immunity.
Other cells such as dendritic cells
(found in lymphoid tissues), monocytes (precursors of
macrophages found in blood) and B lymphocytes found
in the blood and in different lymphoid organs, such
as the lymph nodes) may also function as antigen-presenting
cells. Although the different APCs can be found in different
locations of the organism and present different morphology,
all of them are able to perform the following activities
1. ingest macromolecules and microbes;
2. internalize these antigens into the APCs phagosome;
3. process (digest) the antigens into peptides;
4. export the processed peptides to the APC surface
and present the processed peptides to the B and/or T
lymphocytes, in a non-specific way; the presentation
of the processed antigen to the lymphocytes occurs after
an interaction of the peptide with a protein that belongs
to an important group of molecules known as the Major
Histocompatibility Complex (MHC), the MHC class
II molecule (see belowMHC molecules).
B lymphocytesare cells that carry
some classes of antibodies on their surface and are
capable of differentiating into plasma cells, which
secrete antibodies against a specific antigen. The antibody
binds to microorganisms which somehow managed to escape
from the innate (non-specific) immune mechanisms. After
binding, the antibody activates the complement system
and the phagocytic cells (mainly neutrophils, monocytes
and macrophages) leading to the destruction of the microorganisms.
The formation of an antibody occurs as follows : each
B lymphocyte is programmed to make antibodies with only
one specificity (i.e. all antibodies of one B cell have
the same recognition site) which are placed on the cell
surface as receptors. When an antigen enters the body,
it encounters an endless number of B lymphocytes all
bearing different antibodies with their own individual
recognition site. The antigen binds to the B cell bearing
an antigen-specific antibody, activates it (with the
help of T cells, see below) and causes clonal proliferation
and maturation to plasmocytes. The antibodies secreted
by the plasma cells present the same specificity to
those that reacted with the B cell receptor.
T lymphocytes Many
microorganisms, like viruses, some bacteria and fungi,
live inside host cells where it is impossible for the
antibodies to reach them. However, most virally infected
cells (and some infected by other microorganisms) display
the viral antigens on the surface of the infected cell,
which in turn can be recognized by the T cells. T lymphocytes,
or T cells, mediate cellular immunity, which protects
the individual against intracellular microorganisms
(some bacteria and fungi species, as well as virus)
and tumor cells.
Analogous to B cells, T cells
have their own typical antigen receptor called the T
cell receptor (TCR). The TCR recognizes a complex present
on the surface of APC cells or target cells, consisting
of an antigenic peptide in association with a protein
that belongs to the MHC group of molecules. Binding
of the T cell receptor to this antigen-MHC complex results
in a metabolic alteration within the T cell, the sort
of which depends on the intracellular compartment in
which the pathogen resides.
There are two main T cell subsets:
the T helper cells (Th) and the cytotoxic
T cells (Tc).
lymphocytes which express on their surface a molecule
named CD4; thus in some instances these cells are also
referred to as CD4+ T cells. Th cells respond to specific
antigenic stimulation (i.e. the binding of antigen to
the TCR) by secreting cytokines, such as interleukin-4
(IL-4), interleukin-5 (IL-5), interferon-g, (IFN-g).
Some of these cytokines, secreted through the Th activation,
stimulate B cells to respond more effectively to antigens,
in their antibody production. Other cytokines, such
as the IFN-g, secreted by other Th cells stimulate macrophages
in their responses to antigens, activating them to kill
the microorganism in a more effective way.
Tc cells - are T lymphocytes
that express a molecule named CD8 on their surfaces,
are effector cells and they act by destroying only those
cells whose antigen/peptides are complexed with MHC
class I molecules (and expressed in the surface of the
infected cell) they can recognize. Tc cells can also
recognize and destroy foreign MHC alone, thus being
responsible for graft rejections.
The Major Histocompatibility Complex
Class I and class II MHC molecules are encoded by genes
and are also responsible for acceptance or rejection
of transplanted tissue. The genes of the major histocompatibility
complex encode for three different types of proteins:
class I, class II and class III, the last of which do
not work as antigen presenting molecules but mostly
are directly or indirectly related to immune defense
functions. Although the term MHC is used for the genetic
region at a certain chromosome that encodes for the
antigen presenting molecule, sometimes it is applied
to the antigen presenting molecule itself
An essential aspect is that the MHC
molecules are highly polymorphic and unique to each
individual, except for identical twins. This great variability
in MHC molecules between individuals is caused by several
variable amino acids in the MHC molecule. This phenomenon
is based on the fact that the genes of loci encoding
for a certain MHC molecule, can have many alternative
forms, i.e. many alleles, which explains the distinct
allotypes each individual presents, as unique as each
MHC molecules are essential for reactions
of immune recognition. Different MHC molecules are recognized
by different T cells. Tc cells, involved in recognition
and destroying/rejecting virally infected cells and
foreign tissue grafts, recognize the complex MHC class
I molecules-antigen or the MHC class I alone of foreign
cells (grafts). These Tc cells, helped by the Th cells,
will then destroy the infected cells and/or the foreign
It should be noted that Tc cells will
kill viral infected cells, if they can see viral antigens
complexed with its own MHC class I molecule. If the
Tc cell sees an antigen in conjunction with
a MHC molecule of a different allotype (from a different
person), it will not be able to recognize and destruct.
Thus antigen recognition by the Tc cells is restricted
to MHC class I molecules.
Class I molecules are present on
almost all cells of the body. This is an important evolutionary
acquisition since virally infected cells may occur in
any cell type of our organism.
On the other hand, MHC class II proteins
are more restricted than class I molecules and they
are only present on cells involved in the immune response,
e.g. B cells, APCs and macrophages. This also makes
sense since these molecules are involved in the presentation
of antigens to Th cells by B cells, APCs and macrophages.
These Th cells once activated (after seeing
the antigen-MHC class II complex) will cooperate with
B cells to induce antibody production and they can also
release lymphokines, which help macrophages to kill
Antibodies, generically referred to as immunoglobulins,
are glycoproteins found in the blood and other biological
fluids as soluble proteins and as membrane-bound proteins
on the surface of cells, especially on B lymphocytes.
Each immunoglobulin is essentially bifunctional: it
binds specifically to molecules (antigen) from a pathogen/foreign
substance that elicited the immune response and recruits
other cells and molecules to destroy the pathogen or
non-self molecule, to which the antibody is bound.
Each function is accomplished in
separate structural regions of the antibody molecule.
The region which binds the antigen is the variable region
(which displays an aminoacid sequence which varies considerably,
according to the antigenic determinant which specifically
can fit into it) and the part which recruits
cells and other molecules is the constant region. Some
characteristic variations in the aminoacid sequences
of the constant parts (also called domains) of the immunoglobulins
distinguish different classes or isotypes of antibodies.
The different classes of immunoglobulins have different
characteristics and functions.
Once a B cell expressing a specific
antibody interacts with an antigen, it will divide many
times and some of them will differentiate into plasma
cells and produce antibodies, while others will differentiate
into long-lived B cells, called memory cells.
These memory cells will rapidly expand and secrete high
amounts of specific antibody after encountering the
same antigen again; this type of response is known as
secondary response or anamnestic response. Secondary
responses explain why a second encounter with an antigen
is much more effective and explains why we become immunized
after having some types of infection or when we are
vaccinated. In addition, the antibody produced in the
secondary anamnestic response is of a different isotype
than the antibody produced in the primary response.
There are five isotypes of antibody in humans:
IgG antibodies account for about 75% of the total serum
immunoglobulin in normal adults and are the predominant
antibodies produced in the secondary anamnestic response.
IgG antibodies are found as soluble immunoglobulins
in serum and other biological fluids, and can bind to
certain types of cells, such as macrophages, via a receptor
specific to the constant region of the IgG molecule.
The binding of antigen to IgG so bound to macrophages
can induce the cell to phagocyte the antigen/antibody
IgM antibodies account for about 10%
of the total serum antibodies and are largely confined
to the intravascular spaces. IgM molecules are the first
antibodies to appear after a primary immune response.
Antibodies of this class are very effective at activating
the complement system by a pathway dependent on the
antigen-antibody interaction, the so called classical
pathway, and in this way, are very effective at clearing
bacteria and some fungi from the blood.
IgA is the main immunoglobulin class
in secretions, such as the tears, milk, colostrum, and
mucosal surfaces. It is also the second most abundant
immunoglobulin class in serum but its effectiveness
at mucosal surfaces is unique. IgA antibodies do not
fix complement, although they are important in the neutralization
of some toxins and microorganisms, such as bacterial
toxins and viruses.
IgD immunoglobulins are detected
in blood at very low concentrations by using very sensitive
methods. They are mainly present as membrane-bound immunoglobulins
on the surface of mature B cells where they are co-expressed
with IgM molecules. At present, the function of IgD
is somewhat unclear.
IgE immunoglobulins are found in extremely
low concentrations in the blood. However, they are found
on the surface membrane of basophils and mast cells.
IgE molecules are bound to the mast cells and basophils
via special receptors on the surface of these cells,
specific for the amino terminal region of IgE molecule.
IgE antibody levels in serum are highly increased in
patients infected with helminthic diseases, such as
Ascaris lumbricoides and so there are indications
that this immunoglobulin class plays an important role
in the defense against some helminth species.
All of these antibody molecules act
co-operatively along with a number of other recognition
molecules (the MHC molecules, the TCR, CD4 and CD8 molecules,
various cytokines, the complement system and other molecules
not mentioned in this brief overview). Also the various
cells of the immune system cooperate to bring together
the effector cells and/or humoral activities with the
microorganism, their toxins, or the host infected cells.
The end result is, provided antigen has been recognized
and processed appropriately, the killing of the microorganism
or the infected cell.
Until now, the immune system was presented as an wonderful
system, capable of quite effectively defending the body
against non-self molecules and cells, thus
preserving our body integrity. However, the immune system
can also be the source of many pathological conditions
that can arise through deficiencies of the immune system,
as well as by excessive activation or aberrant activation
of the cells and molecules of the immune system. In
these cases, the immune system itself can be the cause
of pathological conditions. These pathological conditions
include autoimmune diseases, reactions against grafts,
hypersensitivities and allergies, some responses to
tumours and some immunodeficiency disorders, including
Autoimmune diseases arise
when our organism produces aberrant T cells or antibodies
that are able to react with antigens present in our
own cells or tissues.
Autoimmune diseases, mainly those
in which autoimmunity contributes to, or has an association
with, the pathogenesis of the disease, can be classified
into two broad, but overlapping, groups: organ-specific
and non-organ-specific (or systemic) autoimmune diseases.
In the first type, autoimmunity is directed against
one organ. Examples of organ-specific autoimmune diseases
include, among others, Hashimotos thyroiditis
(thyroid gland), pernicious anemia (stomach), Addisons
disease (adrenal glands). In systemic disorders, autoimmunity
is widely spread throughout the body. Examples of systemic
autoimmune diseases include rheumatoid arthritis, systemic
lupus erythematosus (SLE or lupus), and dermatomyositis.
Some autoimmune diseases fall between these two polar
Autoimmune processes can lead to
slow destruction of a specific type of cells or tissue,
stimulation of an organ into excessive growth, or interference
in its function. Organs and tissues frequently affected
include the endocrine glands (such as the thyroid, pancreas,
and adrenal glands), components of the blood (such as
red blood cells), and connective tissues (skin, muscles,
The disease may be mediated by antibodies,
immunecomplexes and/or by T cells. For example, in myasthenia
gravis, antibodies directed to the acetylcholine receptor
found in neuromuscular junctions, lead to muscle weakness
and death. In SLE, immune complexes are formed with
DNA-antibodies directed to DNA and complement components;
these complexes can deposit on the walls of small blood
vessels causing vasculitis in various organs. When these
immunecomplexes are deposited in the kidney glomeruli,
severe damage to the kidneys may occur. Rheumatoid arthritis
is characterized by the presence of Rheumatoid Factors
(RF); these RF are IgM antibodies directed against the
patients own immunoglobulins. In cases of insulin-dependent
(juvenile) diabetes mellitus, the presence of cytotoxic
T cells specific for surface proteins of the beta cells
of the pancreas prevents these cells from producing
occur when the immune response is exaggerated or inappropriate
and causes tissue damage. One hypersensitivity reaction
type is allergy, which occurs when some usually
innocuous substances, such as dust, pollen, drugs, or
some foods are recognized as non-self and
the immune system mounts an inappropriate response to
them, giving rise to symptoms of hypersensitivity. Allergy
occurs when an IgE response is directed against an innocuous
antigen. Upon a second contact with this same antigen,
the pre-formed IgE bound to mast cells react with the
antigen and this reaction will trigger the release of
pharmacological mediators from the mast cells. The release
of these pharmacological mediators (e.g. histamine)
produces an acute inflammatory reaction. Symptoms of
allergy are highly varied, because different allergens
stimulate the immune system at different sites in the
body. The respiratory tract is the most common site
of allergic reactions, with allergens in the upper airways
causing sneezing and nasal congestion (rhinitis, hay
fever), while allergens in the lower airways cause the
bronchoconstriction typically found during asthma episodes.
Food allergens cause immune activation in the gastrointestinal
tract, leading to nausea, vomiting, abdominal cramps,
and diarrhea. Local immune activation in the skin results
in contact dermatitis. Anaphylaxis is the most serious
form of hypersensitivity reaction and it occurs when
an allergen enters the circulation and causes allergic
manifestations at sites distant from the site of entry.
In severe anaphylaxis, the normal body functions are
disrupted to the point that the patient may die.
Hypersensitivity can also occur during
infections. In some instances the amount of damage produced
by the immune response to a resistant microorganism
may be even worse than that produced by the infection
In addition to autoimmune diseases
and hypersensitivity reactions, rejection of transplants
is another condition caused by detrimental effects of
the immune response. As mentioned above, MHC proteins
are powerful tools for our organism to recognize antigens
in our own cells context, and to mount an immune
response toward foreign substances. These same molecules,
however, can elicit the powerful responses that are
responsible for the rejection of grafts and organ transplants
from one individual to another. A graft is permanently
accepted only when most of the histocompatibility antigens
are present in the recipient of the graft. If the recipient
lacks the transplantation antigens, he/she will mount
immune responses to those antigens and the resulting
reactions will lead to the destruction or rejection
of the graft.
Graft rejections are primarily mediated
by cytotoxic T cells, inflammatory Th cells, or both.
We could see that aberrant or exaggerated
immune responses can be detrimental and even fatal.
Similarly, the immunodeficiencies are usually
severe diseases and some of them are fatal. Some of
the severe deficiencies of the immune system are inheritable.
Others are congenital or acquired later in life. Acquired
immunodeficiencies are sometimes a consequence of the
destruction of the blood cells by drugs and radiation
used to treat cancer. However, the most common acquired
immunodeficiency in the last two decades has been AIDS,
which is associated with infection by the HIV (human
Recurrent infections are the most
conspicuous symptoms of immunodeficiencies. Besides
AIDS, other immunodeficienciesgenetic, congenital
or acquiredmay occur and they can be ascribed
to antibody, complement, APCs or T cells deficiencies.
Some examples of immunodeficiencies include X-linked
agammaglobulinemia, severe combined immunodeficiency
syndrome, common variable immunodeficiency, and other
is a genetic disease linked to the X chromosome and
is seen in very young children. The patients do not
have plasma cells and cannot form any type of antibody
after infection or immunization. However, the T cell
compartment remains intact and these children can therefore
recover from some viral diseases, in which the T cells
present the most prominent role.
Severe combined immunodeficiency
disease (SCID) is also an inherited disease, characterized
by recurrent infections that appear a few months after
birth. There are different types of SCID: some are inherited
as an X-linked disorder while others are inherited in
an autosomal recessive way. Infections with common virus
(such as varicella, herpes) as well as atempts to inject
live vaccines, may lead to death. This is a typical
T cell deficiency: the number of circulating T cells
is low and sometimes serum immunoglobulin levels are
Common variable immunodeficiency
is characterized by unusual infections and low levels
of serum immunoglobulins, antibodies. The cause of the
disease is not well known, although it is already clear
that it is not induced by a single defect since B lymphocytes
may be either absent or reduced, helper T lymphocytes
may be deficient or another set of T lymphocytes (not
discussed herein), the suppressor T lymphocytes, may
be excessive. Unlike X-linked agammaglobulinemia, common
variable immunodeficiency is not inherited in a single,
well-defined pattern. This condition is a relatively
common form of immunodeficiency, and the particular
antibody deficiency (IgG alone, both IgG and IgA, or
IgG, IgA and IgM together) can vary from patient to
patient. Not only does the disorder range from severe
to mild, but it can also occur at any age.
This article and the previous ones published in this
series are intended to provide very basic information
about immunology to my translator colleagues, in such
a way that they can understand some concepts, as well
as some expressions and words used by immunologists.
I hope these articles and the accompanying glossary
will help other translators, when they face texts on
immunology and related sciences.
If you have any questions, comments or suggestions for
further topics in the field of immunology or immunology
nomenclature, please contact the author at: email@example.com or at
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