Download ANTIBODY IMMUNE RESPONSE

Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
1. Antibody immune response and regulation
Each B lymphocyte is able to produce only antibodies of one specifity. After the activation by relevant epitope,
B lymphocyte proliferates and differentiates (clonal selection). Because only a few lymphocytes are specific for
a given antigen, T cells and B cells need to migrate throughout the body to increase the probability that they will
encounter that particular antigen. (lymphocytes spend only about 30 minutes in the blood during each cycle
around the body)
.
Summary of B cells development:
Rearrangement of genes for H chain and surface expression of pre - BCR (µ+ψL)
Successful rearrangement of genes for L chain and surface expression of IgM (BCR)
Immature B lymphocytes- testing for potential autoreaction
Somatic mutation and affinity maturation – only the cells with the highest binding affinity to antigen will survive
B1 lymphocytes - the first cells originating during ontogenesis. The most of B1 lymphocytes express membrane
marker CD5 on their surface. B1 lymphocytes are source of so called natural antibodies of IgM class (isotype).
B2 lymphocytes - majority population. After B2 lymphocytes become memory cells, they usually start
expressing IgG, IgA or IgE as their antigen - specific receptor.
Epitopes of B lymphocytes – T independent 1 (TI-1) B cell antigens – e.g. bacterial 1lipopolysaccharide causes
polyclonal activation of BCRs. TI-2 – polymers or repetitive structures, which react with large number of BCRs.
T dependent antigens (TD) – induce primary and secondary immune response resulting in memory cells and
antibodies with high binding affinity to antigen.
Primary antibody response – stimulation of B lymphocytes through BCR, activation of Th lymphocytes mediated
by antigen presenting cells (MHC class II molecule + protein). Activation of B lymphocytes results in antibody
formation with low affinity to antigen (IgM isotype). Immunocomplexes IgM and antigen accumulate on the
surface of follicular dendritic cells (FDC).
Secondary antibody response – recognition of antigens, which are present on the surface of FDC in primary
lymphoid follicles; signals from Th lymphocytes, another proliferation and differentiation of B lymphocytes,
mutation of V genes for H and L chains (somatic mutation). Clones of B lymphocytes with partially altered
biding sites for antigen arise (in comparison with entering cells), only B lymphocytes with the highest affinity
for antigen survive. Isotype switch – rearrangement of genes for constant domains of H chain, which locates new
CH sequence next to exon V/D/J must be performed to express different isotype as µ or δ.
Antibody function:
Neutralization
Opsonization
Complement activation
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05/05/2017
Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
2. Immune reactions of T cells – Th1, Th2 reactions, cytotoxic reactions, regulatory
roles of T cells, NK and NKT cells, onco-immunology.
T cells are the central population of the immune system. Cytotoxic CD8+ T cells recognize the antigen presented
by MHC class I molecules. An example of antigen presented by MHC class I molecules to cytotoxic T cells are
viral particles. CD8+ T cells are activated by the recognition of viral antigens and induce apoptotic cascade in
infected cells leading to their destruction and to the elimination of viral infection. Apoptotic cascade can be
induced by molecular pathways such as Fas-FasL, perforine-granzyme, lymphotoxin etc.
Another population of T cells are CD4+ T cells. CD4+ T cells recognize the antigens presented by MHC class II
molecules expressed on the professional antigen presenting cells. CD4+ T cells are also called T - helpers for
their capacity to actively interact with other cell populations. Originally naïve Th0 cells mature into either Th1 or
Th2 profile. Th1 cells produce interferon-gamma and participate in the inflammatory reactions. Th1 cells
potentate further maturation of Th0 cells into the Th1 profile, induce proinflammatory functions of macrophages
and induce the maturation of dendritic cells by CD40-CD154 pathway.
The hallmark of Th2 cells is the production of IL-4 and IL-13. Th2 cells induce the maturation of B cells into
plasmatic cells and their production of antibodies by direct cell-to-cell contact (CD40-CD154 interaction) or by
cytokines.
Regulatory T cells constitute a separate subpopulation of T cells. The group of regulatory T cells involves
naturally occurring regulatory T cells - CD4+CD25+ T cells and NKT cells. The other subgroup of regulatory T
cells can be induced by the specific conditions of the immune responses. A typical example of induced
regulatory T cells are Th3 CD4+ T cells producing regulatory cytokines TGF-beta an IL-10. Th3 CD4+ T cells
are induced by the oral antigen administration.
NK cells are the cells of the innate immune system. Their activation is antigen non-specific and they do not
require the presentation of antigen by MHC molecules. NK cells participate in the elimination of viral infections
(mainly herpes viruses) and tumour cells.
Morphological and functional failures of T cell populations and their misbalances can induce the development of
several diseases.
The failures of regulatory T cells are involved in the rupture of self-tolerance and the development of
autoimmune diseases. Patients suffering from autoimmune diseases often exhibit decreased numbers of
regulatory T cells and decreased function of the residual populations of regulatory T cells.
Th1-Th2 balance is impaired in several types of diseases. The Th2 profile dominates in allergic diseases, Th1
profile of the immune response is characteristic for autoimmune diseases such as type 1 diabetes mellitus,
multiple sclerosis and others.
The immune system can recognize and destroy tumour cells by the action of NK and cytotoxic T cells. The
increasing incidence of oncological disorders witnesses the capacity of tumour cells to avoid the attack of
immune system – due to the production of suppressive cytokines (TGF-beta), downregulation of MHC
molecules on the surface of tumour cells and others. The stimulation of the immune system of oncological
patients or even the vaccination with tumour antigens represents the hopes for the treatment of oncological
disorders.
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Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
3. The inflammation, the immune reaction
The basic functions of the immune system is the defense against environmental, usually infectious agents,
defense against dangerous agents originated in own body such as tumor cells and the regulation of the immune
response (the prevention of the reaction of immune system against own tissues).
The elimination of infections agents is due to the cooperation of cells and mediators of both innate and adaptive
immune system. The innate immune system recognizes evolutionary old, conserved structures on pathogen
surface (pathogen associated molecular pattern). These molecules (lipopolysaccharide for example) are
expressed by bacteria whereas they are never expressed on the surface of eukaryotes. The recognition of PAMP
by the cells and mediators of innate immunity leads to the rapid development of immune reaction and usually to
the elimination of infectious agents. The innate immune system involves neutrophils, macrophages, NK cells etc.
The typical mediator of innate immunity is complement – a cascade of proteins that generates active mediators
by the cleavage of inactive precursors. The active complement mediators have cytotoxic, opsonic and other
functions.
The hallmark of the adaptive immunity is the specific recognition of antigen determinants by the receptor of T or
B cells. The antigen recognition activates T or B cells and induces their clonal expansion – the expansion of cells
able to recognize the same antigen. A disadvantage of this reaction is its relative slowness. However, when the
adaptive immune system is exposed to the same antigen for the second time, the reaction is much more rapid and
very efficient. This hallmark of the adaptive immune system is cold the immunologic memory and it is the base
of the vaccines against many infectious diseases.
Transplantation immunology, immunology of reproduction and gestation.
Transplantation medicine replaces damaged tissues and organs of one patient by the tissues of donors of various
immunogenetic matching. The immune system of recipient can perceive the grafts as a foreign and can develop
the immune reaction leading to graft rejection. The goal of transplantation medicine/immunology is to suppress
the “physiological” immune reaction and to promote the graft acceptation. The basic strategy in this field is to
choose the donor-recipient pairs with the highest matching in ABO and HLA system and the use of
immunosuppressive drugs.
The gametes are the potential target of the immune reaction and the immunity can contribute to the some cases
of infertility. The sperms are protected from the attack of the immune system by the specific structural and
immunologic features of testicles such as the specific cytokine milieu, the expression of Fas-L and others. The
damage of specific testicular morphological or functional features by inflammation or trauma can lead to the
subsequent destruction of sperms and infertility.
The sperms can also be destroyed by the immune system of the female during their migration to the ovum in
genital female tract.
Another example of the participation of the immune system in the gestational complications is the Rh
incompatibility. Rh positive fetus can induce the generation of anti Rh IgG antibodies by the Rh negative mother
leading very often to the premature interruption of the gestation.
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Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
4. Mucosal immunity
The function of mucosal immunity: defense against infectious pathogens, the barrier against penetration of
infectious and immunogenic agent to the circulation, low reactivity against non pathogenic antigens and the
maintenance of mucosal immune homeostasis.
Characteristics of mucosal immunity:
Strong participation of innate immunity
Characteristic populations of T cells
Tolerance of luminal antigens
Homing of mucosal and exocrine tissues
Transport of polygenic immunoglobulins through epithelium – secretory immunoglobulins
The mucosal immune system contains 80% immune cells. There are 10 14 bacteria on the mucous surfaces and
more than 1000 bacterial species.
The mucosal immune system contains organized lymphoid tissues – MALT (mucosa associated lymphoid
tissues). The mucosal surfaces and mucosal immune system represent a huge surface communicating with
environment.
A hallmark of the mucosal immune system is to distinguish between non-pathogenic – commensally and
pathogenic microbes. The pathogens are identified due to the recognition of their conserved structures - PAMP
(pathogen associated molecular pattern) by the PRR (pattern recognition receptors).
PRR include mannose receptor, scavenger receptors, CD14 receptor for polysaccharide, complement receptors
etc.
Toll like receptors – a subgroup of PRR. Originally described in insects, identification of bacterial antigens such
as LPS, CpG etc. The recognition by TLR induces the gene replication, transcription etc leading to the
development of the immune responses.
The colonization of mucosal surfaces by the bacteria is an important factor for the development of adaptive
immunity.
The antigens are transported from the intestinal lumen by M cells – specialized population of enterocytes. The
antigens are then captured and processed by antigen presenting cells and B cells in subepithelial spaces. The
antibodies of class A are produced by B cells localized in germinal centers of follicular zones.
The secretory IgA and IgM neutralize antigens on mucosal surfaces (immune inclusions). The secretory IgA do
not activate, that might damage mucosa. The immunocomplexes of IgA can be captured on APC and induce the
immune response (immune elimination).
The immune response against orally administrated antigen depends on the genetic background of individuum,
the type of commensally bacteria and the type of the immune reaction. The majority of orally administrated
antigens induce the suppression of specific immunity (oral tolerance).
Many chronic immune-disorders develop due to the failures of mucosal immunity and tolerance.
Autoimmunity
Autoimmunity develops due to the failure of immune tolerance.
The mechanisms of immune tolerance:
Thymic tolerance
Positive selection in thymus - cells survive by binding to MHC molecules (cells which bind with low affinity to
MHC therefore they have a potential to bind to MHC plus foreign protein with high affinity)
Negative selection - cells which bind to MHC plus self peptides with high affinity have a potential of induction
autoimmunity. These cells are eliminated
Limitation of the central tolerance
Many self peptides are not expressed in the thymus
Thymic tolerance is not induced to many tissue specific proteins (in the brain, muscle, joints, islet of
Langerhans) - autoreactive T cells to many tissue-specific proteins can be detected in healthy people
Mechanisms of peripheral tolerance
Immunological ignorance
Many of antigens are invisible to the immune system (intact vitreous humor of the eye). Limited distribution of
these molecules (on APC) means that most organ specific molecules will not be presented to CD4+ T cells at
levels high enough to induce T-cell activation.
Separation of autoreactive T cells and autoantigens
Naive lymphocytes are kept in circulation between blood and secondary lymphoid tissue.
Debris from self tissue breakdown is cleared rapidly by apoptosis, function of complement system and
phagocytosis (defects of complement of phagocytes are associated with the development of autoimmunity
against intracellular molecules)
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Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
Suppression
Active suppression of self reactive T-cells by inhibitory populations of T cells which – Treg cells. The best
defined mechanism involved cytokines from Th2 cells specifically inhibiting a Th1 response (IL-4, IL-10)
B-cell tolerance
At the peripheral level - if newly developed or recently hypermutated B cells bind the appropriate antigen in the
absence of T-cell help then the B cell will undergo apoptosis or anergy.
Anergy and costimulation
Deletion of self-reactive cells by apoptosis
Classification of autoimmune reaction
Characterization of antigen
Detection of autoantibodies or autoreactive T cells
The reproduction of the process in vitro
The reproduction of the disease on experimental model
The autoimmune reaction involves:
1. Humoral immunity – antibodies, usually IgG, cytotoxic effect, development of immunocomplexes, functional
changes of cells and proteins, the binding of antibodies on the receptors – stimulation or inhibition of receptors.
2. Cellular immunity – lymphocytes, phagocytes and their cytokines. Mechanism – inflammation, tissue damage,
participation of CD8+ T cells, CD4 T cells, macrophages and cytokines.
Autoimmune reaction:
Physiologic – maintenance of immune – homeostasis (damaged cells). Low concentration, low affinity,
polyspecifity, domination of IgM isotype. The concentration increases with age.
Pathologic – high concentration, high-affinity IgG, IgA. Questionable participation of IgG in tissue
damage.
Autoimmune diseases
1. Organ non-specific autoimmune disease
Affect multiple organs and is directed against molecule widely distributed through the body, particularly
intracellular molecules involved in transcription and translation of the genetic code.
2. Organ specific – target one or few specific tissues/organs (Hashimoto thyroiditis, Type 1 Diabetes Mellitus).
Etiology of autoimmunity is unknown
1. Genetic factors of autoimmunity: multiple genes, (MHC-HLA B27, DR3 etc, VNTR)
Genes encoding for cytokines, apoptosis, polymorphism of TCR, gene for H chain of Ig etc.
2. Environmental factors:
Infection agents – EBV – B cells, Superantigens. Mechanism of molecular mimicry – structural and antigen
similarities between self-antigens and epitopes of microorganisms can initiate autoimmune reaction
(streptococcal M protein, heart myosin, Coxsackie virus – GAD).
Pathologic expression of HLA class II on cells (induced by IFN-, medicaments, UV etc)
Laboratory tests
Detection of antibodies against autoantigens, test of autoreactivity of T cells. Detection of antibodies is used for
the laboratory diagnosis of autoimmune diseases.
Detection of autoantibodies against nuclear antigens by indirect fluorescence.
Type of fluorescence on Hep-2 cells, antibodies and associated disorders
Type of fluorescence
Homogenous
Peripheral
Granulomatous
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Antinuclear antibodies
anti-histon
anti-dsDNA
anti-dsDNA
anti-laminin
anti-U1 RNP
anti-Sm
anti-La
anti -Ro
anti-PCNA/cyklin
anti-KU
anti-Scl-70
Disease
SLE, RA, DI-SLE, JCA
SLE
SLE
SLE
MCTD, SLE
SLE
SS, SLE, seldom RA
SS, SLE, newborn lupus, seldom RA
SLE
SLE, PSS/DM
PSS
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Study materials, Course Immunopathology, Module IIA
Nuclear
Homogenous
Cytoplasmatic
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antiribozomal RNP
anti-PM-Scl
anti-U3RNP (fibrilarin)
anti-RNA polymerase I
anti-centromera
anti-tRNA syntetasa
(JO-1, PL-7, PL-12 atd.)
anti-ribozomal RNP
anti-Ro
antimitochondrial
Institute of Immunology, 3rd Medical Faculty, CHU
SLE
PSS/DM
PSS
PSS
CREST
PM/DM
SLE
SLE
PBC
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Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
5. Immunodeficiency – molecular mechanisms of primary ID
Causes of impaired immunity
Primary
missing enzyme
missing cell type
missing component (no function)
(usually in childhood, severe)
Secondary
caused by other disease – lymphoid malignancy,
infection ( HIV)
malnutrition, glomerulopathy, protein loss by GIT, burns
immunosupresive therapy
Types of molecular defect related to primary immunodeficiency
Disease/Syndrome
Phenotype defect
Mutant gene
B, T cells receptor
Gen defect -complex CD3
AR agamaglobulinemia
Selective defect Ig
Ig only with  chains
gene for CD3  or  chain
genes for  chain 14q32.3
gene defect for HC 14q 32.3
gene defect for  chain 2p11
Defect TCR
B cells Absence
Ig isotypes absence
Deficiency  chain
Deficiency of chain of cytokine receptor
X linked SCID
T-B+NK+ SCID
Autosomal recesive SCID
T-B+NK- SCID
Defect of one element of ligand pair
X linked Hyper IgM syndrome
Deficiency of IgG,
gene for  chain common.
receptor Xq13.1
gene for  chain IL-7R 5p13
gene CD154 (CD40
ligand) Xq26.3
IgA, increased IgM
Defects of signal molecules
X linked agamaglobulinemia
Autosom. rec. SCID
CD8 lymphopenia
X linked lymphoprolif,
ZAP-70 deficiency
EBV induced lymphoprolif
Wiskott-Aldrich syndrome
ID, trombocytopenia,ekzema
gene for Btk Xq21.3
gene for Jak3 19p13.1
CD45 tyrosin phosphatase
RAG1, RAG2 6q21.3
TAP1, TAP2 6q21.3
TAP1, TAP2 6q21.3,
gene for transcription factors
RFXAP, CIITA, RFXANK
gene for ZAP-70 2q12
gene pro SH2D1A adapter
protein Xq25
gene for WASP Xp11.23
Metabolic defect
SCID AR
T-B-NK-adenosine deaminase
gene for ADA 20q13.2
MHC class I defect
MHC class II defect
Absence of B cells
T-B+NKT-B+NKT-B-NK+
MHC I
A. Antibody deficiency
Very low production of Ig isotypes. Infections caused by common bacterial pathogens (Strepto, Pneumococcus,
Hemofilus infl.)
B. Combined immunodeficiency
First weeks, months of life, etiology viral, fungal. Frequent chronic diarrhea, airway infection, soor
Failure to thrive
C. Complement disorders
Decreased activity of C is usually secondary after activation of C cascade – consumption in IC diseases - SLE
(consumption of C1, C4, C2)
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Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
Primary, inborn defects: Defect of early components - C1, C2, C4 – deteriorate the capacity of C solubilize IC
- immunocomplex disease, similar to lupus (malar rash, arthralgia, GN, chronic vasculitis, rare pyogenic
infection. (ANA, anti-dsDNA missing)
D,B,P defect
recurrent Neisserial infection
C3 defect
recurrent bacterial infection
C1 Inactivator defect Hereditary angioedema
D. Defects of phagocytosis
- amount or function defect of neutrophils usually involved
Infections are recurrent and long-lasting, Clinical symptoms are unusually mild, in comparison with severe
infection. Poor response to antibiotics
Frequent cause : Staphylococci, Enterobacteria, fungi (Aspergillus, Candida albicans)
Skin and mucosa involved, complicated by suppurative lymphadenopathy
Types of the defect
– enzyme defect - chronic granulomatous disease (low reactive metabolites production - defect
NADPH oxidase), no bactericidal function
– defects of adhesive molecules
- LAD syndrome – deficiency of leukocyte integrins complex CD11b/CD18 on leucocytes
(gene for beta 2 subunit)
- LAD2 – defect of CD15 – expression of sialyl-LewisX
Immunopathologic reactions of hypersenzitivity
Tissue damage due to immunopathology reactions
Side effect ( necessary) of the defense reactions against dangerous pathogens
Exaggerated reactions against harmless exogenous antigens (allergy, hypersensitivity)
Aberrant immune reaction against normal autoantigens (autoimmune reactions)
Correlates of normal and abnormal immune reactions
Immune mechanism
Physiological
Ab binding
Opsonization
and activation of C
Pathogen lysis
IgE production,
mast cell activation
Th1, macrophages
activation
Antiparasitic
defense
Defense against
IC pathogens
Pathology
Opsonization
Self cell
destruction
Allergy inflam.
Anaphylaxis
Autoimmunity
Self-destruction
during infection
Tissue damage caused by the immune system – Types of immunopathologic reactions
Types of immunopathologic reactions
Mechanism
Disease
Immediate
(Type I)
1. IgE production, mast cell degranulation
Anaphylaxis
2. Late phase of allergic inflammation
Atopic diseases
- influx of inflammatory cells (Eo)
Mediators: Histamine, Leukotrienes
Cell bound Ag
(Type II)
IgG/IgM antibodies
cytotoxic
Complement lysis
Neutrophil activation
Opsonization
Metabolic stimulation
Blocking Ab
Immunocomplex reaction
(Type III)
concentration of IC
due to persistent Ag, Ab production,
complement activation and inflammation
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AIHA
ABO, Rh incompatibility
Goodpasture sy
Cold AIHA, ITP
Graves’ disease
Myasthenia gravis, Pernicious anemia
Serum sickness
Extrinsic A.Alv (farmers lung)
Lepromatous leprosy
SLE
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Study materials, Course Immunopathology, Module IIA
Institute of Immunology, 3rd Medical Faculty, CHU
Cutaneous vasculitis
Delayed hypersenzitivity
(Type IV)
Th1 cytokine production
Attraction of Ly, Macrophages by cytokines
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Graft rejection
Tuberculosis, contact
dermatitis
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