Functional organization of the Immune System

Presented byPresented by

Dr. B. Victor, Dr. B. Victor,

St. Xavier’s College,St. Xavier’s College,

Palayamkottai-627002,India.Palayamkottai-627002,India.

Antibodies Antibodies (or Immunoglubulins)(or Immunoglubulins)

• The chemical information of immunoglobulin The chemical information of immunoglobulin

was provided by was provided by Tiselius and KabatTiselius and Kabat in the early in the early 1940s.1940s.

• In 1950s, In 1950s, Porter and EdelmanPorter and Edelman revealed the revealed the basic structure of immunoglobulin molecule.basic structure of immunoglobulin molecule.

• Antibodies are products of Antibodies are products of antigen- activated antigen- activated B- lymphocytes.B- lymphocytes.

• They are the They are the main effectors of humoral main effectors of humoral immunityimmunity..

• They bind antigens with They bind antigens with high specificity and high specificity and affinity.affinity.

Antibodies are products of Antibodies are products of antigen- antigen- activated B- lymphocytesactivated B- lymphocytes

Subclasses of human Subclasses of human immunoglobulinsimmunoglobulins

There areThere are nine nine chemically distinct classes of human chemically distinct classes of human immunoglobulins, immunoglobulins, four kinds of IgG and two kinds of four kinds of IgG and two kinds of IgA, plus IgM, IgE, and IgD.IgA, plus IgM, IgE, and IgD.

The classes of human immunoglobulins are based on The classes of human immunoglobulins are based on structure and function. structure and function. IgM -secreted during primary response IgM -secreted during primary response IgG -secreted during secondary response IgG -secreted during secondary response IgD -receptors for antigens on B cells IgD -receptors for antigens on B cells IgA -found in external secretions IgA -found in external secretions IgF -promotes histamine releaseIgF -promotes histamine release

Immunoglobulins G, D, and E are similar in Immunoglobulins G, D, and E are similar in appearance. appearance.

Kinds of ImmunoglobulinKinds of Immunoglobulin

ImmunoglobulinImmunoglobulin• This glycoprotein is This glycoprotein is Y-shaped moleculesY-shaped molecules and has two and has two

identical binding sites for its antigen, one on either arm identical binding sites for its antigen, one on either arm of the Y. of the Y.

• This protein is composed of This protein is composed of four polypeptide chainsfour polypeptide chains (two (two identical heavy chains and two identical and smaller identical heavy chains and two identical and smaller light chains) held together by disulfide bonds. light chains) held together by disulfide bonds. - - two identical light chainstwo identical light chains (L chains), each containing (L chains), each containing about 200 amino acids about 200 amino acids – two identical heavy chainstwo identical heavy chains (H chains), each made up (H chains), each made up

of 400 amino acids.of 400 amino acids.– Each chain is made up of several different domains. Each chain is made up of several different domains.

• The The antigen-binding siteantigen-binding site is formed where a heavy chain is formed where a heavy chain variable domain (VH) and a light chain variable domain variable domain (VH) and a light chain variable domain (VL) come close together. (VL) come close together.

• These are the domains that differ most in their These are the domains that differ most in their sequence and structure in different antibodies. sequence and structure in different antibodies.

The variable (V) regionsThe variable (V) regions..

• The first 100 or so amino acids at the N-terminal of The first 100 or so amino acids at the N-terminal of both H and L chains vary greatly from antibody to both H and L chains vary greatly from antibody to antibody. antibody. These are the variable (V) regionsThese are the variable (V) regions. . – The amino acid sequence variability in the V The amino acid sequence variability in the V

regions is especially pronounced in 3 regions is especially pronounced in 3 hypervariable regions. hypervariable regions.

– Together they construct the antigen binding site Together they construct the antigen binding site against which the epitope fits against which the epitope fits

• Only a few different amino acid sequences are found Only a few different amino acid sequences are found in the C-terminals of H and L chains. in the C-terminals of H and L chains.

• These are the constant (C) regions. These are the constant (C) regions.

The constant (C) regions.The constant (C) regions. • Humans make Humans make

– two different kinds of C regions for their L chains two different kinds of C regions for their L chains producing producing � kappa (κ) L chains kappa (κ) L chains � lambda (λ) L chainslambda (λ) L chains

– five different kinds of C regions for their H chains five different kinds of C regions for their H chains producing producing � mu (µ) chains (the H chain of IgM antibodies) mu (µ) chains (the H chain of IgM antibodies) � gamma (γ) chains (IgG) gamma (γ) chains (IgG) � alpha (α) chains (IgA) alpha (α) chains (IgA) � delta (δ) chains (IgD) epsilon (ε) chains (IgE)delta (δ) chains (IgD) epsilon (ε) chains (IgE)

Fc and Fab regions Fc and Fab regions

• The proteolytic enzyme papain breaks each The proteolytic enzyme papain breaks each Ig molecule into 3 fragments at the hinge Ig molecule into 3 fragments at the hinge region.region.

• The single crystallizable fragment (Fc region) The single crystallizable fragment (Fc region) includes part of the constant domain that includes part of the constant domain that occupies the stem.occupies the stem.

• There are 2 antigen-binding fragments (Fab There are 2 antigen-binding fragments (Fab region), which include the entire light chain region), which include the entire light chain and variable and constant portions of the and variable and constant portions of the heavy chain.heavy chain.

• Ig GIg GPapain

2 Fab + Fc

Antibody StructureAntibody Structure

ImmunoglobulinImmunoglobulin

ImmunoglobulinImmunoglobulin

Immunoglobulin GImmunoglobulin G

•. IgG,IgG, 150,000 MW, 75% of serum Ig 150,000 MW, 75% of serum Ig,, the major the major immunoglobulin in the blood, is also able to immunoglobulin in the blood, is also able to enter tissue spaces; Four classes; it works enter tissue spaces; Four classes; it works efficiently to coat microorganisms, speeding efficiently to coat microorganisms, speeding their destruction by other cells in the immune their destruction by other cells in the immune system. antibodies to toxins, bacteria and system. antibodies to toxins, bacteria and viruses. Crosses the placenta to give the viruses. Crosses the placenta to give the newborn some passive immunity. newborn some passive immunity.

Bacteriolytic Viricidal

Precipitating ab

Immunoglobulin AImmunoglobulin A

•IgA-IgA--a doublet--guards the entrance to the body. -a doublet--guards the entrance to the body. 170,000 MW in serum and 400,000 MW in external 170,000 MW in serum and 400,000 MW in external secretions, 15% of Ig in serum, found in the blood as secretions, 15% of Ig in serum, found in the blood as a monomer, and in tears, saliva, colustrum, nasal, a monomer, and in tears, saliva, colustrum, nasal, vaginal, prostatic and bronchial secretions as a vaginal, prostatic and bronchial secretions as a dimer.dimer.• Blocks attachment of microbes to mucous Blocks attachment of microbes to mucous membranesmembranes• It concentrates in body fluids such as tears, saliva, It concentrates in body fluids such as tears, saliva, and secretions of the respiratory and and secretions of the respiratory and gastrointestinal tracts.gastrointestinal tracts.

Secretary abFirst line defense

for microbes

Immunoglobulin MImmunoglobulin M

•IgM IgM usually combines in star-shaped clusters. pentamer,usually combines in star-shaped clusters. pentamer,•It tends to remain in the bloodstream, 10% of blood Ig,It tends to remain in the bloodstream, 10% of blood Ig,• found on the surface of B lymphocytes. found on the surface of B lymphocytes. •Activates the complement system.Activates the complement system.

Macroglobulinprimary immune response

Bacteriolytic

Immunoglobulin DImmunoglobulin D

• 180,000 MW, activity is not well known. 0.2% 180,000 MW, activity is not well known. 0.2% of plasma Ig. 13% carbohydrate content. Also of plasma Ig. 13% carbohydrate content. Also found on the surface of B lymphocytesfound on the surface of B lymphocytes, , where where it somehow regulates the cell's activationit somehow regulates the cell's activation

Membrane bound antibodyFound on B-cell membrane

Memory function

Immunoglobulin EImmunoglobulin E

• !90 000 MW, largest immunoglobulin, present in !90 000 MW, largest immunoglobulin, present in extremely low levels in a healthy individual.extremely low levels in a healthy individual.

• IgE levels rise in response to parasitic  infections and in IgE levels rise in response to parasitic  infections and in  allergic reactions. allergic reactions.

• Bind and activate mast cells. Mast cells cause acute Bind and activate mast cells. Mast cells cause acute inflammatory response (e.g. swelling, redness, pain and inflammatory response (e.g. swelling, redness, pain and itchiness). itchiness). 

• Hay fever is a condition caused by too much IgE activity.Hay fever is a condition caused by too much IgE activity.

Activate mast cellsRelease vasoactive amines

Respond to allergensMediate hypersensitivity

reactions

Human immunoglobulin isotype monomers.

Defense mechanisms of Defense mechanisms of antibodiesantibodies

1. Opsonization1. Opsonization2. MAC Cytolysis2. MAC Cytolysis3. Antibody-dependent Cellular 3. Antibody-dependent Cellular Cytotoxicity (ADCC) Cytotoxicity (ADCC) by NK Cellsby NK Cells4. Neutralization of Exotoxins4. Neutralization of Exotoxins5. Neutralization of Viruses5. Neutralization of Viruses6. Preventing Bacterial Adherence to Host 6. Preventing Bacterial Adherence to Host CellsCells7. Agglutination of Microorganisms7. Agglutination of Microorganisms8. Immobilization of Bacteria and 8. Immobilization of Bacteria and Protozoans.Protozoans.

CytokinesCytokinesNon- antibody proteinsNon- antibody proteins produced by cells of produced by cells of the immune system (including T cells, B the immune system (including T cells, B cells, monocytes, and macrophages). cells, monocytes, and macrophages). Cytokines include a Cytokines include a diverse groupdiverse group of of interleukinsinterleukins, , interferonsinterferons, and , and growth factorsgrowth factors..cytokines are cytokines are chemical switcheschemical switches that turn that turn certain immune cell types on and off.certain immune cell types on and off.One cytokine, interleukin 2 (IL-2), triggers One cytokine, interleukin 2 (IL-2), triggers the immune system to produce T cells. the immune system to produce T cells. Cytokines also are being studied for their Cytokines also are being studied for their potential potential clinical benefitclinical benefit..

Functions of cytokinesFunctions of cytokines Activation of the Immune Activation of the Immune Cells Cells

Promotion of Cell Growth, meaning Promotion of Cell Growth, meaning maturation, and/or division maturation, and/or division

Attraction of Cells to the site of Attraction of Cells to the site of infection infection

Destruction Infected or Malignant Destruction Infected or Malignant CellsCells

Stimulation of Phagocytic Activity Stimulation of Phagocytic Activity

Kinds of cytokinesKinds of cytokines

1. 1. Monokines -Monokines - produced by mononuclear produced by mononuclear phagocytesphagocytes

2. 2. Lymphokines -Lymphokines - produced by activated T produced by activated T cells, primarily helper T cellscells, primarily helper T cells

3. 3. InterleukinsInterleukins -- name given to many name given to many cytokines, abbreviated as IL and given a cytokines, abbreviated as IL and given a

numbernumber

ChemokinesChemokines

1.1. The name chemokine is a contraction of The name chemokine is a contraction of chemochemotactic cytotactic cytokineskines

2.2. These are a large family of substances These are a large family of substances (more than 50) produced by many (more than 50) produced by many different different leukocytes and tissue cellsleukocytes and tissue cells

3.3. They recruit leukocytes to sites of infectionThey recruit leukocytes to sites of infection

4.4. They play a role in lymphocyte traffickingThey play a role in lymphocyte trafficking

PropertiesProperties1.Produced by cells involved in both natural

and specific immunity2. Mediate and regulate immune and

inflammatory responses3. Secretion is brief and limited4. Many individual cytokines are produced by

many cell types and act on many cell types (they are pleiotropic)

5. In many cases cytokines have similar actions (they are redundant).

PropertiesProperties6. 6. Often influence the synthesis of other Often influence the synthesis of other

cytokines cytokines a.a. They can produce cascades, or enhance or They can produce cascades, or enhance or

suppress production of other cytokinessuppress production of other cytokinesb.b. They exert positive or negative regulatory They exert positive or negative regulatory

mechanisms for immune and inflammatory mechanisms for immune and inflammatory responsesresponses

7. Often influence the action of other 7. Often influence the action of other cytokines. Effects can be:cytokines. Effects can be:

a.a. AntagonisticAntagonisticb.b. AdditiveAdditivec.c. greater than additive (synergistic)greater than additive (synergistic)

PropertiesProperties8. Bind to specific receptors on target cells 8. Bind to specific receptors on target cells with with high affinity. Compare with antigen high affinity. Compare with antigen binding binding to antibody or peptide binding to a to antibody or peptide binding to a MHC MHC molecule which both show much molecule which both show much lower lower binding affinities.binding affinities.9. Cells that can respond to a cytokine are:9. Cells that can respond to a cytokine are:a. same cell that secreted cytokine: autocrinea. same cell that secreted cytokine: autocrineb. a nearby cell: paracrineb. a nearby cell: paracrinec. a distant cell reached through the circulation: c. a distant cell reached through the circulation:

endocrineendocrine

10. Cellular responses to cytokines are 10. Cellular responses to cytokines are generally slow (hours), require newgenerally slow (hours), require new mRNA mRNA and protein synthesisand protein synthesis

Functional types of CytokinesFunctional types of Cytokines

• Cytokines can be grouped according to functionCytokines can be grouped according to function• 1. Mediators and regulators of Natural Immunity1. Mediators and regulators of Natural Immunity

     Tumor Necrosis Factor (TNF)     Tumor Necrosis Factor (TNF)     Interleukin-1 (IL-1)     Interleukin-1 (IL-1)     Chemokines     Chemokines     Interleukin-10     Interleukin-10     Interferon-gamma (IFN-gamma)     Interferon-gamma (IFN-gamma)

• 2. Mediators and regulators of specific immunity2. Mediators and regulators of specific immunity     Interleukin-2 (IL-2)     Interleukin-2 (IL-2)     Interleukin-4 (IL-4)     Interleukin-4 (IL-4)     Interleukin-5 (IL-5)     Interleukin-5 (IL-5)     Interleukin-10 (IL-10)     Interleukin-10 (IL-10)     Interferon-gamma (IFN-gamma)     Interferon-gamma (IFN-gamma)

• 3. Stimulators of hematopoeisis3. Stimulators of hematopoeisis     Interleukin-3 (IL-3)     Interleukin-3 (IL-3)     Colony-Stimulating Factors (CSFs)     Colony-Stimulating Factors (CSFs)

Tumor Necrosis Factor,Tumor Necrosis Factor, TNF-gammaTNF-gamma

  • produced by activated macrophagesproduced by activated macrophages•   the most important mediator of acute the most important mediator of acute

inflammation inflammation in response to Gram-negative in response to Gram-negative bacteria and  other bacteria and  other infectious microbesinfectious microbes

• mediates the recruitment of polymorphonuclear mediates the recruitment of polymorphonuclear leukocytes (PMNs) and monocytes to the  site leukocytes (PMNs) and monocytes to the  site

of of infection: infection: • acts on the hypothalamus to produce feveracts on the hypothalamus to produce fever• promotes the production of acute phase proteins promotes the production of acute phase proteins

by the liverby the liver

Interleukin-2Interleukin-2

• produced mainly by helper T cells produced mainly by helper T cells (CD4+); less by cytoxic T cells (CD8+)(CD4+); less by cytoxic T cells (CD8+)

• promote T cell division and increase promote T cell division and increase production of other cytokinesproduction of other cytokines

• has autocrine functions on T cell has autocrine functions on T cell proliferation.proliferation.

Interleukin-4Interleukin-4

• Produced mainly by Th2 subpopulation Produced mainly by Th2 subpopulation of helper T cells (CD4+).  of helper T cells (CD4+). 

• Stimulates immunoglobulin class Stimulates immunoglobulin class switching to the IgE isotype.  switching to the IgE isotype. 

• Stimulates development of Th2 cells Stimulates development of Th2 cells from naive CD4+ T cellsfrom naive CD4+ T cells

• promotes growth of differentiated Th2 promotes growth of differentiated Th2 cellscells

Interleukin-5Interleukin-5

• produced mainly by the Th2 produced mainly by the Th2 subpopulation of helper T cells (CD4+)subpopulation of helper T cells (CD4+)

• promotes growth and differentiation of promotes growth and differentiation of eosinophilseosinophils

• activates mature eosinophilsactivates mature eosinophils

Interferons (IFN)Interferons (IFN)

There are three groups of interferons:  There are three groups of interferons:  IFN-IFN-alpha , IFN-beta , IFN-gamma alpha , IFN-beta , IFN-gamma 

• IFN-alphaIFN-alpha:  Twenty  variants are produced by :  Twenty  variants are produced by leukocytes in response to virusesleukocytes in response to viruses

• IFN-beta:IFN-beta: This is a single protein produced by This is a single protein produced by fibroblasts and other cells in response to fibroblasts and other cells in response to virusesviruses

• Both IFN-alpha  and IFN-beta   inhibit viral Both IFN-alpha  and IFN-beta   inhibit viral replication and increase expression of class I replication and increase expression of class I MHC on cellsMHC on cells

IFN-gamma:IFN-gamma:• produced by  the Th1 subpopulation of helper T cells produced by  the Th1 subpopulation of helper T cells

(CD4+), cytotoxic T cells (CD8+), and NK cells. (CD4+), cytotoxic T cells (CD8+), and NK cells. •   IFN-gamma functions in both natural and specific IFN-gamma functions in both natural and specific

immunityimmunity• Natural Immunity-Natural Immunity- IFN-gamma enhances the IFN-gamma enhances the

microbicidal function of macrophages microbicidal function of macrophages • Specific Immunity-Specific Immunity- IFN-gamma stimulates the IFN-gamma stimulates the

expression of class I and class II MHC molecules and expression of class I and class II MHC molecules and co-stimulatory molecules on antigen presenting cellsco-stimulatory molecules on antigen presenting cells- IFN-gamma promotes the differentiation of naive - IFN-gamma promotes the differentiation of naive helper T cells into Th1 cells helper T cells into Th1 cells - IFN-gamma activates polymorphonuclear - IFN-gamma activates polymorphonuclear leukocytes (PMN) and cytotoxic T cells and increases leukocytes (PMN) and cytotoxic T cells and increases the cytotoxicity of NK cells.the cytotoxicity of NK cells.

Transforming Growth FactorTransforming Growth Factor (TGF-beta) (TGF-beta)

• an inhibitory cytokine produced by T cells, an inhibitory cytokine produced by T cells, macrophages, and many other cell types.macrophages, and many other cell types.

• inhibits proliferation and differentiation of inhibits proliferation and differentiation of T cellsT cells

• inhibits activation of macrophagesinhibits activation of macrophages• acts on PMN and endothelial cells to block acts on PMN and endothelial cells to block

the effects of pro-inflammatory cytokinesthe effects of pro-inflammatory cytokines

Stimulators of Hematopoiesis :Stimulators of Hematopoiesis :

1. Interleukin-31. Interleukin-3- produced by helper T cells- produced by helper T cells -promotes growth and differentiation of bone marrow -promotes growth and differentiation of bone marrow progenitorsprogenitors

2. Colony-Stimulating Factors (CSFs)2. Colony-Stimulating Factors (CSFs)- produced by T cells, macrophages, endothelial cells, fibroblasts- produced by T cells, macrophages, endothelial cells, fibroblasts3.Granulocyte-macrophage colony-stimulating factor 3.Granulocyte-macrophage colony-stimulating factor (GM-CSF)(GM-CSF) -promotes growth and differentiation of bone marrow progenitors-promotes growth and differentiation of bone marrow progenitors4. Macrophage colony-stimulating factor (M-CSF4. Macrophage colony-stimulating factor (M-CSF)) -the development and function of monocytes/macrophages-the development and function of monocytes/macrophages5.Granulocyte colony-stimulatory factor (G-CSF5.Granulocyte colony-stimulatory factor (G-CSF)) -stimulates the production of PMN-stimulates the production of PMN

Complement ProteinsComplement Proteins

• They circulate through the bloodstream in They circulate through the bloodstream in an inactive form. an inactive form.

• When the complement cascade is When the complement cascade is triggered ( by the presence of antibody-triggered ( by the presence of antibody-antigen complexes), components of the antigen complexes), components of the cascade are successively activated, to: cascade are successively activated, to:

Stimulate Mast Cells and Basophils to release Stimulate Mast Cells and Basophils to release granulocytic chemicals granulocytic chemicals Attract Neutrophils to the area Attract Neutrophils to the area Opsonize Invading Microbes Opsonize Invading Microbes Generate a Membrane Attack Complex, Generate a Membrane Attack Complex,

The complement systemThe complement system

The complement system helps clear pathogens from an organism.

It is derived from many small plasma proteins that form the biochemical cascade of the immune system .

Activation of this system leads to cytolysis , chemotaxis , opsonization ,immune

clearence, and inflamation, as well as the marking of pathogens for phagocytosis.

The complement systemThe complement system

The complement system consists of more than The complement system consists of more than 35 35 soluble and cell-bound proteinssoluble and cell-bound proteins ,12 of which are ,12 of which are directly involved in the complement pathways. directly involved in the complement pathways. The proteins account for The proteins account for 5% of the serum globulin 5% of the serum globulin fraction .fraction . Most of these proteins circulate as Most of these proteins circulate as zymogenszymogens , , which are inactive until proteolytic cleavage . which are inactive until proteolytic cleavage . The complement proteins are The complement proteins are synthesized mainly synthesized mainly by hepatocytesby hepatocytes ; however, significant amounts ; however, significant amounts are also produced by Monocytes, macrophages, are also produced by Monocytes, macrophages, and epithelial cells in the gastrointestinal and and epithelial cells in the gastrointestinal and Genitourinary tracts.Genitourinary tracts.

Biochemical pathways of the Biochemical pathways of the complement system:complement system:

the classical complement pathway the classical complement pathway

the alternate complement pathway the alternate complement pathway

the manon-binding –lectin pathwaythe manon-binding –lectin pathway

Pathways of Pathways of complement activationcomplement activation

CLASSICALPATHWAY

ALTERNATIVEPATHWAY

activationof C5

LYTIC ATTACKPATHWAY

antibodydependent

LECTINPATHWAY

antibodyindependent

Activation of C3 andgeneration of C5 convertase

The Complement SystemThe Complement System

The Complement SystemThe Complement System

Figure 16.10

Secretory molecules of Secretory molecules of non-specific immunity non-specific immunity

These include:These include: • organic acids in skin secretions,organic acids in skin secretions,• thiocyanate in saliva, thiocyanate in saliva, • low molecular weight fatty acids in the low molecular weight fatty acids in the

lower bowel; lower bowel; • bile acids and low molecular weight fatty bile acids and low molecular weight fatty

acids in lower GI tract; acids in lower GI tract; • transferrin, lactoferrin, lysozyme, transferrin, lactoferrin, lysozyme,

interferons, fibronectin, complement, acute interferons, fibronectin, complement, acute phase proteins, etc. in serum; phase proteins, etc. in serum;

• Interferons and tumor necrosis factor (TNF) Interferons and tumor necrosis factor (TNF) at the site of inflammation.at the site of inflammation.

Secretory molecules of Secretory molecules of non-specific immunity non-specific immunity

• Transferrin and lactoferrin deprive organisms of iron.  • Interferon inhibits viral replication and activates other cells

which kill pathogens • Lysozyme, in serum and tears, breaks down the bacterial cell

wall (peptidoglycan) • Fibronectin coats (opsonizes) bacteria and promotes their

rapid phagocytosis.  • Complement components and their products cause

destruction of microorganism directly or with the help of phagocytic cells. Acute phase proteins (such as CRP) interact with the complement system proteins to combat infections. 

• TNF-alpha suppresses viral replication and activates phagocytes.

About the presenterAbout the presenter• Dr.B.Victor is a highly experienced postgraduate Dr.B.Victor is a highly experienced postgraduate

biology teacher, recently retired from the reputed biology teacher, recently retired from the reputed educational institution St. Xavier’ s College, educational institution St. Xavier’ s College, Palayamkottai, India-627001.Presently HOD of Biotech Palayamkottai, India-627001.Presently HOD of Biotech at Annai Velankanni college, Tholayavattam. K .K Distat Annai Velankanni college, Tholayavattam. K .K Dist

• He was the dean of sciences and assistant controller of He was the dean of sciences and assistant controller of examinations of St. Xavier’s college.examinations of St. Xavier’s college.

• He has more than 32 years of teaching and research He has more than 32 years of teaching and research experience and has guided more than 12 Ph. D experience and has guided more than 12 Ph. D scholars.scholars.

• He has taught Immunology and biochemistry to He has taught Immunology and biochemistry to graduate and post graduate students.graduate and post graduate students.

• Send your comments to : [email protected] your comments to : [email protected]