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An introduction to immunology and immunopathology

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In basic terms, the immune system has two lines of defense: innate immunity and adaptive immunity. Innate immunity is the first immunological, non-specific (antigen-independent) mechanism for fighting against an intruding pathogen. It is a rapid immune response, occurring within minutes or hours after aggression, that has no immunologic memory. Adaptive immunity, on the other hand, is antigen-dependent and antigen-specific; it has the capacity for memory, which enables the host to mount a more rapid and efficient immune response upon subsequent exposure to the antigen. There is a great deal of synergy between the adaptive immune system and its innate counterpart, and defects in either system can provoke illness or disease, such as autoimmune diseases, immunodeficiency disorders and hypersensitivity reactions. This article provides a practical overview of innate and adaptive immunity, and describes how these host defense mechanisms are involved in both health and illness.
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REVIEW Open Access
An introduction to immunology and
immunopathology
Richard Warrington
1*
, Wade Watson
2
, Harold L Kim
3,4
, Francesca Romana Antonetti
5
Abstract
In basic terms, the immune system has two lines of defense: innate immunity and adaptive immunity. Innate
immunity is the first immunological, non-specific (antigen-independent) mechanism for fighting against an
intruding pathogen. It is a rapid immune response, occurring within minutes or hours after aggression, that has no
immunologic memory. Adaptive immunity, on the other hand, is antigen-dependent and antigen-specific; it has
the capacity for memory, which enables the host to mount a more rapid and efficient immune response upon
subsequent exposure to the antigen. There is a great deal of synergy between the adaptive immune system and
its innate counterpart, and defects in either system can provoke illness or disease, such as autoimmune diseases,
immunodeficiency disorders and hypersensitivity reactions. This article provides a practical overview of innate and
adaptive immunity, and describes how these host defense mechanisms are involved in both health and illness.
Introduction
Over the past decade, there have been numerous
advances in our current understanding of the immune
system and how it functions to protect the body from
infection. Given the complex nature of this subject, it is
beyond the scope of this article to provide an in-depth
review of all aspects of immunology. Rather, the purpose
of this article is to provide medical students, medical
residents, primary-care practitioners and other health-
care professionals with a basic introduction to the main
components and function of the immune system and its
role in both health and disease. This article will also
serve as a backgrounder to the immunopathological dis-
orders discussed in the remainder of this supplement.
The topics covered in this introductory article include:
innate and acquired immunity, passive and active immu-
nization and immunopathologies, such as hypersensitiv-
ity reactions, autoimmunity and immunodeficiency.
The immune system: innate and adaptive
immunity
The immune system refers to a collection of cells and
proteins that function to protect the skin, respiratory
passages, intestinal tract and other areas from foreign
antigens,suchasmicrobes(organismssuchasbacteria,
fungi, and parasites), viruses, cancer cells, and toxins.
The immune system can be simplistically viewed as hav-
ing two lines of defense: innate immunity and adaptive
immunity. Innate immunity represents the first line of
defense to an intruding pathogen. It is an antigen-inde-
pendent (non-specific) defense mechanism that is used
by the host immediately or within hours of encountering
an antigen. The innate immune response has no immu-
nologic memory and, therefore, it is unable to recognize
or memorizethesamepathogenshouldthebodybe
exposed to it in the future. Adaptive immunity, on the
other hand, is antigen-dependent and antigen-specific
and, therefore, involves a lag time between exposure to
the antigen and maximal response. The hallmark of
adaptive immunity is the capacity for memory which
enables the host to mount a more rapid and efficient
immune response upon subsequent exposure to the
antigen. Innate and adaptive immunity are not mutually
exclusive mechanisms of host defense, but rather are
complementary, with defects in either system resulting
in host vulnerability [1-3].
Innate immunity
The primary function of innate immunity is the recruit-
ment of immune cells to sites of infection and inflam-
mation through the production of cytokines (small
proteins involved in cell-cell communication). Cytokine
production leads to the release of antibodies and other
* Correspondence: RWarrington@exchange.hsc.mb.ca
1
University of Manitoba, Winnipeg, Manitoba, Canada
Full list of author information is available at the end of the article
Warrington et al.Allergy, Asthma & Clinical Immunology 2011, 7(Suppl 1):S1
http://www.aacijournal.com/content/7/S1/S1 ALLERGY, ASTHMA & CLINICAL
IMMUNOLOGY
© 2011 Warringt on et al; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative
Commons Attri bution License (http://creativecommons.org /licenses/by/2.0), which permits unrestricte d use, distribution, and
reproductio n in any medium, provided the original work is properly cited.
proteins and glycoproteins which activate the comple-
ment system, a biochemical cascade that functions to
identify and opsonize (coat) foreign antigens, rendering
them susceptible to phagocytosis (process by which cells
engulf microbes and remove cell debris). The innate
immune response also promotes clearance of dead cells
or antibody complexes and removes foreign substances
present in organs, tissues, blood and lymph. It can also
activate the adaptive immune response through a pro-
cess known as antigen presentation (discussed later)
[1,3].
Numerous cells are involved in the innate immune
response such as phagocytes (macrophages and neutro-
phils), dendritic cells, mast cells, basophils, eosinophils,
natural killer (NK) cells and lymphocytes (T cells). Pha-
gocytes are sub-divided into two main cell types: neutro-
phils and macrophages. Both of these cells share a
similar function: to engulf (phagocytose) microbes. In
addition to their phagocytic properties, neutrophils con-
tain granules that, when released, assist in the elimina-
tion of pathogenic microbes. Unlike neutrophils (which
are short-lived cells), macrophages are long-lived cells
that not only play a role in phagocytosis, but are also
involved in antigen presentation to T cells. Macrophages
are named according to the tissue in which they reside.
For example, macrophages present in the liver are called
Kupffer cells while those present in the connective tissue
are termed histiocytes (see Figure 1) [1].
Dendritic cells also phagocytose and function as anti-
gen-presenting cells (APCs) and act as important mes-
sengers between innate and adaptive immunity. Mast
cells and basophils share many salient features with
each other and both are instrumental in the initiation of
acute inflammatory responses, such as those seen in
allergy and asthma. Unlike mast cells, which generally
reside in the connective tissue surrounding blood ves-
sels, basophils reside in the circulation. Eosinophils are
granulocytes that possess phagocytic properties and play
an important role in the destruction of parasites that are
too large to be phagocytosed. Along with mast cells and
basophils, they also control mechanisms associated with
allergy and asthma. NK cells (also known as large granu-
lar lymphocytes [LGLs]) play a major role in the rejec-
tion of tumours and the destruction of cells infected by
viruses. Destruction of infected cells is achieved through
the release of perforins and granzymes from NK-cell
granules which induce apoptosis (programmed cell
death) [4]. The main characteristics and functions of the
cells involved in the innate immune response are sum-
marized in Figure 1.
Innate immunity can be viewed as comprising four
types of defensive barriers: anatomic (skin and mucous
Cell Image % in adults Nucleus Functions Lifetime Main targets
Macrophage* Varies Varies xPhagocytosis
xAntigen
presentation to T
cells
Months – years xVarious
Neutrophil 40-75% Multi-lobed xPhagocytosis
xDegranulation
(discharge of
contents of a cell)
6 hours – few
days
xBacteria
xFungi
Eosinophil 1-6% Bi-lobed xDegranulation
xRelease of
enzymes, growth
factors, cytokines
8-12 days
(circulate for 4-5
hours)
xParasites
xVarious allergic
tissues
Basophil < 1% Bi- or tri-lobed xDegranulation
xRelease of
histamine,
enzymes,
cytokines
Lifetime
uncertain; likely
a few hours –
few days
xVarious allergic
tissues
Lymphocytes
(T cells)
20-40% Deeply staining,
eccentric
T helper (Th) cells
(CD4+): immune
response mediators
Cytotoxic T cells
(CD8+): cell
destruction
Weeks to years xTh cells: intracellular
bacteria
xCytotoxic T cells:
virus infected and
tumour cells
xNatural killer cells:
virus-infected and
tumour cells
Monocyte 2-6% Kidney shaped Differentiate into
macrophages and
dendritic cells to elicit
an immune response
Hours – days xVarious
Figure 1 Characteristics and function of cells involved in innate immunity [1,3,4]. *Dust cells (within pulmonary alveolus), histiocytes
(connective tissue), Kupffer cells (liver), microglial cells (neural tissue), epithelioid cells (granulomas), osteoclasts (bone), mesangial cells (kidney)
Warrington et al.Allergy, Asthma & Clinical Immunology 2011, 7(Suppl 1):S1
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membrane), physiologic (temperature, low pH and che-
mical mediators), endocytic and phagocytic, and inflam-
matory. Table 1 summarizes the non-specific host-
defense mechanisms for each of these barriers.
Adaptive immunity
Adaptive immunity develops when innate immunity is
ineffective in eliminating infectious agents and the infec-
tion is established. The primary functions of the adap-
tive immune response are the recognition of specific
non-selfantigens in the presence of selfantigens; the
generation of pathogen-specific immunologic effector
pathways that eliminate specific pathogens or pathogen-
infected cells; and the development of an immunologic
memory that can quickly eliminate a specific pathogen
should subsequent infections occur [2]. The cells of the
adaptive immune system include: T cells, which are acti-
vated through the action of antigen presenting cells
(APCs), and B cells.
T cells and APCs
T cells derive from hematopoietic stem cells in bone
marrow and, following migration, mature in the thymus.
These cells express a unique antigen-binding receptor
on their membrane, known as the T-cell receptor
(TCR), and as previously mentioned, require the action
of APCs (usually dendritic cells, but also macrophages,
B cells, fibroblasts and epithelial cells) to recognize a
specific antigen.
The surfaces of APCs express cell-surface proteins
known as the major histocompatibility complex (MHC).
MHC are classified as either class I (also termed human
leukocyte antigen [HLA] A, B and C) which are found
on all nucleated cells, or class II (also termed HLA, DP,
DQ and DR) which are found on only certain cells of
the immune system, including macrophages, dendritic
cells and B cells. Class I MHC molecules present endo-
genous (intracellular) peptides while class II molecules
present exogenous (extracellular) peptides. The MHC
protein displays fragments of antigens (peptides) when a
cell is infected with a pathogen or has phagocytosed for-
eign proteins [2,3].
T cells are activated when they encounter an APC that
has digested an antigen and is displaying antigen frag-
ments bound to its MHC molecules. The MHC-antigen
complex activates the TCR and the T cell secretes cyto-
kines which further control the immune response. This
antigen presentation process stimulates T cells to differ-
entiate into either cytotoxic T cells (CD8+ cells) or T-
helper (Th) cells (CD4+ cells) (see Figure 2). Cytotoxic
T cells are primarily involved in the destruction of cells
infected by foreign agents. They are activated by the
interaction of their TCR with peptide-bound MHC class
I molecules. Clonal expansion of cytotoxic T cells pro-
duce effector cells which release perforin and granzyme
(proteins that causes lysis of target cells) and granulysin
(a substance that induces apoptosis of target cells).
Upon resolution of the infection, most effector cells die
and are cleared by phagocytes. However, a few of these
cells are retained as memory cells that can quickly dif-
ferentiate into effector cells upon subsequent encounters
with the same antigen [2,3].
T helper (Th) cells play an important role in establish-
ing and maximizing the immune response. These cells
have no cytotoxic or phagocytic activity, and cannot kill
infected cells or clear pathogens. However, they med-
iatethe immune response by directing other cells to
Table 1 Summary of non-specific host-defense mechanisms for barriers of innate immunity [1]
Barrier Mechanism
Anatomic
Skin Mechanical barrier retards entry of microbes
Acidic environment (pH 3-5) retards growth of microbes
Mucous
membrane
Normal flora compete with microbes for attachment sites
Mucous entraps foreign microbes
Cilia propel microbes out of body
Physiologic
Temperature Body temperature/fever response inhibits growth of some pathogens
Low pH Acidic pH of stomach kills most undigested microbes
Chemical
mediators
Lysozyme cleaves bacterial cell wall
Interferon induces antiviral defenses in uninfected cells
Complement lyses microbes or facilitates phagocytosis
Phagocytic/endocytic barriers
Various cells internalize (endocytosis) and break down foreign macromolecules
Specialized cells (blood monocytes, neutrophils, tissue macrophages) internalize (phagocytose), kill and digest whole organisms
Inflammatory barriers
Tissue damage and infection induce leakage of vascular fluid containing serum protein with antibacterial activity, leading to
influx of phagocytic cells into the affected area
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perform these tasks. Th cells are activated through TCR
recognition of antigen bound to class II MHC mole-
cules. Once activated, Th cells release cytokines that
influence the activity of many cell types, including the
APCs that activate them.
Two types of Th cell responses can be induced by an
APC: Th1 or Th2. The Th1 response is characterized by
the production of interferon-gamma (IFN-g) which acti-
vates the bactericidal activities of macrophages, and
other cytokines that induce B cells to make opsonizing
(coating) and neutralizing antibodies. The Th2 response
is characterized by the release of cytokines (interleukin-
4, 5 and 13) which are involved in the activation and/or
recruitment of immunoglobulin E (IgE) antibody-produ-
cing B cells, mast cells and eosinophils. As mentioned
earlier, mast cells and eosinophils are instrumental in
the initiation of acute inflammatory responses, such as
those seen in allergy and asthma. IgE antibodies are also
associated with allergic reactions (see Table 2). There-
fore, an imbalance of Th2 cytokine production is asso-
ciated with the development of atopic (allergic)
conditions. Like cytotoxic T cells, most Th cells will die
Figure 2 Adaptive immunity: T-cell and B-cell activation and function. APC: antigen-presenting cell; TCR: T-cell receptor; MHC: major
histocompatibility complex Figure adapted from images available at: http://en.wikipedia.org/wiki/Image:B_cell_activation.png and http://
commons.wikimedia.org/wiki/Image:Antigen_presentation.svg
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upon resolution of infection, with a few remaining as Th
memory cells [2,3].
A third type of T cell, known as the regulatory T cell
(T reg), also plays a role in the immune response. T reg
cells limit and suppress the immune system and,
thereby, may function to control aberrant immune
responses to self-antigens and the development of auto-
immune disease.
B cells
B cells arise from hematopoietic stem cells in the bone
marrow and, following maturation, leave the marrow
expressing a unique antigen-binding receptor on their
membrane. Unlike T cells, B cells can recognize free
antigen directly, without the need for APCs. The princi-
pal function of B cells is the production of antibodies
against foreign antigens [2,3].
When activated by foreign antigens, B cells undergo
proliferation and differentiate into antibody-secreting
plasma cells or memory B cells (see Figure 2). Memory
Bcellsarelong-livedsurvivors of past infection and
continue to express antigen-binding receptors. These
cells can be called upon to respond quickly and elimi-
nate an antigen upon re-exposure. Plasma cells, on the
other hand, do not express antigen-binding receptors.
These are short-lived cells that undergo apoptosis when
the inciting agent that induced the immune response is
eliminated.
Given their function in antibody production, B cells
play a major role in the humoral or antibody-mediated
immune response (as opposedtothecell-mediated
immune response, which is governed primarily by T
cells) [2,3].
Antibody-mediated vs. cell-mediated immunity
Antibody-mediated immunity is the branch of the
acquired immune system that is mediated by B-cell anti-
body production. The antibody-production pathway
begins when the B cells antigen-binding receptor
recognizes and binds to antigen in its native form. This,
in turn, attracts the assistance of Th cells which secrete
cytokines that help the B cell multiply and mature into
antibody-secreting plasma cells. The secreted antibodies
bind to antigens on the surface of pathogens, flagging
them for destruction through pathogen and toxin neu-
tralization, classical complement activation, opsonin
promotion of phagocytosis and pathogen elimination.
Upon elimination of the pathogen, the antigen-antibody
complexes are cleared by the complement cascade (see
Figure 2) [2].
Five types of antibodies are produced by B cells:
immunoglobulin A (IgA), IgD, IgE, IgG and IgM. Each
of these antibodies has differing biological functions and
recognize and neutralize specific pathogens. Table 2
summarizes the various functions of the five Ig antibo-
dies [5].
Antibodies play an important role in containing virus
proliferation during the acute phase of infection. How-
ever, they are not generally capable of eliminating a
virus once infection has occurred. Once an infection is
established, cell-mediated immune mechanisms are
most important in host defense.
Cell-mediated immunity does not involve antibodies,
but rather protects an organism through [2]:
the activation of antigen-specific cytotoxic T cells
that induce apoptosis of cells displaying epitopes (loca-
lized region on the surface of an antigen that is capable
of eliciting an immune response) of foreign antigen on
their surface, such as virus-infected cells, cells with
intracellular bacteria, and cancer cells displaying tumour
antigens;
the activation of macrophages and NK cells, enabling
them to destroy intracellular pathogens; and
the stimulation of cytokine production that further
mediates the immune response.
Cell-mediated immunity is directed primarily at
microbes that survive in phagocytes as well as those that
Table 2 Major functions of human Ig antibodies [5]
Ig
antibody
Function
IgM First immunoglobulin (Ig) expressed during B cell development (primary response; early antibody)
Opsonizing (coating) antigen for destruction
Complement fixation
IgG Main Ig during secondary immune response
Only antibody capable of crossing the placental barrier
Neutralization of toxins and viruses
Opsonizing (coating) antigen for destruction
Complement fixation
IgD Function unclear; appears to be involved in homeostasis
IgA Mucosal response; protects mucosal surfaces from toxins, viruses and bacteria through either direct neutralization or prevention of
binding to mucosal surface
IgE Associated with hypersensitivity and allergic reactions
Plays a role in immune response to parasites
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infect non-phagocytic cells. This type of immunity is
most effective in eliminating virus-infected cells, but can
also participate in defending against fungi, protozoa,
cancers, and intracellular bacteria. Cell-mediated immu-
nity also plays a major role in transplant rejection.
Passive vs. active immunization
Acquired immunity is attained through either passive or
active immunization. Passive immunization refers to the
transfer of active humoral immunity, in the form of
ready-madeantibodies, from one individual to another.
It can occur naturally by transplacental transfer of
maternal antibodies to the developing fetus, or it can be
induced artificially by injecting a recipient with exogen-
ous antibodies targeted to a specific pathogen or toxin.
The latter is used when there is a high risk of infection
and insufficient time for the body to develop its own
immune response, or to reduce the symptoms of
chronic or immunosuppressive diseases.
Active immunization refers to the production of anti-
bodies against a specific agent after exposure to the
antigen. It can be acquired through either natural infec-
tion with a microbe or through administration of a vac-
cine that can consist of attenuated (weakened)
pathogens or inactivated organisms,
Immunopathology
As mentioned earlier, defects or malfunctions in either
the innate or adaptive immune response can provoke ill-
ness or disease. Such disorders are generally caused by
an overactive immune response (known as hypersensi-
tivity reactions), an inappropriate reaction to self
(known as autoimmunity) or ineffective immune
responses (known as immunodeficiency).
Hypersensitivity reactions
Hypersensitivity reactions refer to undesirable responses
produced by the normal immune system. There are four
types of hypersensitivity reactions [6,7]:
Type I: immediate hypersensitivity
Type II: cytotoxic or antibody-dependent
hypersensitivity
Type III: immune complex disease
Type IV: delayed-type hypersensitivity
Type I hypersensitivity is the most common type of
hypersensitivity reaction. It is an allergic reaction pro-
voked by re-exposure to a specific type of antigen,
referred to as an allergen. Unlike the normal immune
response, the type I hypersensitivity response is charac-
terized by the secretion of IgE by plasma cells. IgE anti-
bodies bind to receptors on the surface of tissue mast
cells and blood basophils, causing them to be sensi-
tized. Later exposure to the same allergen, cross-links
the bound IgE on sensitized cells resulting in
degranulation and the secretion of active mediators such
as histamine, leukotriene, and prostaglandin that cause
vasodilation and smooth-muscle contraction of the sur-
rounding tissue. Common environmental allergens indu-
cing IgE-mediated allergies include cat-, dog- and horse
epithelium, pollen, house dust mites and molds. Food
allergens are also a common cause of type I hypersensi-
tivity reactions, however, these types of reactions are
more frequently seen in children than adults. Treatment
of type I reactions generally involves trigger avoidance,
and in the case of inhaled allergens, pharmacological
intervention with bronchodilators, antihistamines and
anti-inflammatory agents. More severe cases may be
treated with immunotherapy.
Type II hypersensitivity reactions are rare and take
anywhere from 2 to 24 hours to develop. These types of
reactions occur when IgG and IgM antibodies bind to
the patients own cell-surface molecules, forming com-
plexes that activate the complement system. This, in
turn, leads to opsonization, red blood cell agglutination
(process of agglutinating or clumping together), cell
lysis and death. Some examples of type II hypersensitiv-
ity reactions include: erythroblastosis fetalis, Goodpas-
tures syndrome, and autoimmune anemias.
Type III hypersensitivity reactions occur when IgG
and IgM antibodies bind to soluble proteins (rather than
cell surface molecules as in type II hypersensitivity reac-
tions) forming immune complexes that can deposit in
tissues, leading to complement activation, inflammation,
neutrophil influx and mast cell degranulation. This type
of reaction can take hours, days, or even weeks to
develop and treatment generally involves anti-inflamma-
tory agents and corticosteroids. Examples of type III
hypersensitivity reactions include systemic lupus erythe-
matosus (SLE), serum sickness and reactive arthritis.
Unlike the other types of hypersensitivity reactions,
type IV reactions are cell-mediated and antibody-inde-
pendent. They are the second most common type of
hypersensitivity reaction and usually take 2 or more
days to develop. These types of reactions are caused by
the overstimulation of T cells and monocytes/macro-
phages which leads to the release of cytokines that
cause inflammation, cell death and tissue damage. In
general, these reactions are easily resolvable through
trigger avoidance and the use of topical corticosteroids.
A brief summary of the four types of hypersensitivity
reactions is provided in Table 3.
Autoimmunity
Autoimmunity involves the loss of normal immune
homeostasis such that the organism produces an abnor-
mal response to its own tissue. The hallmark of autoim-
munity is the presence of self-reactive T cells, auto-
antibodies, and inflammation. Prominent examples of
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autoimmune diseases include: Celiac disease, type 1 dia-
betes mellitus, Addisons disease and Gravesdisease [8].
Immunodeficiency
Immunodeficiency refers to a state in which the
immune systems ability to fight infectious disease is
compromised or entirely absent. Immunodeficiency dis-
orders may result from a primary congenital defect (pri-
mary immunodeficiency) or may be acquired from a
secondary cause (secondary immunodeficiency), such as
viral or bacterial infections, malnutrition or treatment
with drugs that induce immunosuppression. Certain dis-
eases can also directly or indirectly impair the immune
system such as leukemia and multiple myeloma. Immu-
nodeficiency is also the hallmark of acquired immuno-
deficiency syndrome (AIDS), caused by the human
immunodeficiency virus (HIV). HIV directly infects Th
cells and also impairs other immune system responses
indirectly [9,10].
Conclusion
Innate immunity is the first immunological, non-specific
mechanism for fighting against infections. This immune
response is rapid, occurring minutes or hours after
aggression and is mediated by numerous cells including
phagocytes, T cells, mast cells, basophils and eosino-
phils, as well as the complement system. Adaptive
immunity develops in conjunction with innate immunity
to eliminate infectious agents; it relies on the tightly
regulated interplay between T cells, APCs and B cells. A
critical feature of adaptive immunity is the development
of immunologic memory or the ability of the system to
learn or record its experiences with various pathogens,
leading to effective and rapid immune responses upon
Table 3 Types of hypersensitivity reactions [6,7]
Type Alternate name Examples Mediators
I Allergy (immediate) Atopy
•—Anaphylaxis
•—Asthma
•—Allergic rhinitis
•—Angioedema
•—Food allergy
IgE
II Cytotoxic, antibody-dependent Erythroblastosis fetalis
Goodpastures syndrome
Autoimmune anemias,
thrombocytopenias
IgG, IgM
III Immune complex disease Systemic lupus erythematosus
Serum sickness
Reactive arthritis
Arthrus reaction
Aggregation of antigens IgG, IgM
Complement proteins
IV Delayed-type hypersensitivity, cell-mediated, antibody-
independent
Contact dermatitis
Tuberculosis
Chronic transplant rejection
T cells, monocytes, macrophages
Table 4 Overview of the defining features of innate and adaptive immunity [1]
Innate immune system Adaptive immune system
Cells Hematopoietic cells:
macrophages
dendritic cells
mast cells
neutrophils
basophils
eosinophils
NK cells
T cells
non-hematopoietic cells
epithelial cells (skin, airways, gastrointestinal tract)
Hematopoietic cells:
T cells
B cells
Molecules cytokines
complement
proteins and glycoprotein
antibodies (Ig)
cytokines
Response time immediate delayed by hours to days
Immunologic memory none: responses are the same with each exposure responsiveness enhanced by repeated antigen exposure
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subsequent exposure to the same or similar pathogens.
A brief overview of the defining features of innate and
adaptive immunity are presented in Table 4.
There is a great deal of synergy between the adaptive
immune system and its innate counterpart, and defects
in either system can lead to immunopathological disor-
ders, including autoimmune diseases, immunodeficien-
cies and hypersensitivity reactions. The remainder of
this supplement will focus on the appropriate diagnosis,
treatment and management of some of these more pro-
minent disorders, particularly those associated with
hypersensitivity reactions.
Acknowledgements
The authors would like to extend special thanks to the Serono Symposia
International Foundation, whose accredited online course entitled An
Introduction to Immunologyprovided the foundation and framework for
this article. This informative, entry-level course was authored by Dr.
Francesca Antonetti and can be accessed through the Serono Symposia
International Foundation website at: http://www.seronosymposia.org/en/
Immunology/OnlineCourses/page.html
The authors would like to thank Julie Tasso for her editorial services and
assistance in the preparation of this manuscript.
This article has been published as part of Allergy, Asthma & Clinical
Immunology Volume 7 Supplement 1, 2011: Practical guide for allergy and
immunology in Canada. The full contents of the supplement are available
online at http://www.aacijournal.com/supplements/7/S1
Author details
1
University of Manitoba, Winnipeg, Manitoba, Canada.
2
Dalhousie University,
Division of Allergy, IWK Health Centre, Halifax, Nova Scotia.
3
McMaster
University, Hamilton, Ontario, Canada.
4
University of Western Ontario,
London, Ontario, Canada.
5
Medical Oncology, Department of Internal
Medicine, Tor Vergata Clinical Centre, University of Rome, Rome, Italy.
Competing interests
Dr Richard Warrington is the past president of the Canadian Society of
Allergy & Clinical Immunology and Editor-in-Chief of Allergy,Asthma &
Clinical Immunology. He has received consulting fees and honoraria from
Nycomed, CSL Behring and Talecris.
Dr. Wade Watson is a co-chief editor of Allergy,Asthma & Clinical
Immunology. He has received consulting fees and honoraria for continuing
education from AstraZeneca, GlaxoSmithKline, King Pharma, Merck Frosst,
and Nycomed.
Dr. Harold Kim is the past president of the Canadian Network for Respiratory
Care and co-chief editor of Allergy,Asthma & Clinical Immunology. He has
received consulting fees and honoraria for continuing education from
AstraZeneca, GlaxoSmithKline, Graceway Pharmaceuticals, King Pharma,
Merck Frosst, Novartis, and Nycomed.
Dr. Francesca Antonetti has written articles for Merck Serono.
Published: 10 November 2011
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doi:10.1186/1710-1492-7-S1-S1
Cite this article as: Warrington et al.: An introduction to immunology
and immunopathology. Allergy, Asthma & Clinical Immunology 2011 7
(Suppl 1):S1.
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