IMMUNE RESPONSE

DEEPA BABIN TMC KOLLAM

A tribute to

A TRIBUTE TO (L-R) 2011 Nobel Prize winners for Physiology or Medicine Bruce A. Beutler, Jules A. Hoffmann , Ralph M. Steinman

Nobel Prize winners Bruce A. Beutler, Jules A. Hoffmann

for their discoveries concerning the activation of innate immunity" Ag binds the Toll like receptors in body cells and activates innate immunity-inflammation

and the other half to Ralph M. Steinman "for

his discovery of the dendritic cell activates T cell and its role in adaptive immunity".

The Immune response An immune response is what the

immune system does when confronted by an antigen.

An immune response is an elaborate interplay between antigen, non-specific defenses, and B and T lymphocytes.

The process involves direct contact (cells, molecules bind to receptors on cell surfaces) and cytokines (messenger molecules) that also bind to receptors on cell surfaces

Immune Response

Innate response – by birth, limited in its response (cannot handle too much invasion)

Adaptive Immune response– Matures over person’s lifetime– Takes time to start up– More effective and very powerful– Important Hallmark : MEMORY– Complex, involves a network of cells:

cytokines, B cells, T cells, antibodies

Adaptive Immune Response

2 types

- Humoral/ antibody mediated (AMI) immunity

- Cell mediated immunity (CMI)

Humoral Immunity - Applications

Defense against most extracellular bacterial pathogens viruses that infect through the

respiratory or intestinal tracts

Prevents recurrence of viral infections.

Takes part in the pathogenesis of Immediate (Types 1, 2 & 3) hypersensitivity & certain autoimmune disorders.

Humoral Immunity

Cells taking part in immune response - Antigen presenting cells

(APCs) - B cells & - T cells

Production of antibodies consists of following stages :

1. Ag capture & processing by APCs2. Ag presentation3. TH cell activation4. B cell stimulation & differentiation5. Ab production by plasma cells

1. Antigen Capture & Processing

Captured by APCs (macrophages & dendritic cells) – broken down in to small peptides.

The immune response begins when a white blood cell called a macrophage encounters a virus and consumes it. Meanwhile, other viruses look for nearby cells to infect.

Next, the macrophage digests the virus and displays pieces of the virus called antigens on its surface. Nearby cells have now become infected by theattacking viruses.

2. Antigen Presentation

Peptides derived from1. Exogenous Ags – presented with MHC

class II molecule, recognised by TH cells.

2. Endogeous Ags – presented with MHC class I molecule, recognised by TC cells.

Capture, Processing and Presentation of Antigen by an Antigen presenting cell (APC)

Capture, Processing and Presentation of Antigen by an Antigen presenting cell (APC)

This union stimulates the production of chemical substances -- such as interleukin-1 (IL-1) and tumor necrosis factor (TNF) by the macrophage, and interleukin-2 (IL-2) and gamma interferon (IFN-y) by the T cell – that allow intercellular communication

3. Helper T cell Activation Activation requires 2 signals:1. Combination of TCR with the Ag

peptide-MHC class II complex.2. Co-stimulatory signal : combination

of B7 on APC & CD28 on the T cell with release of IL-1 .

Activated TH cells now produce IL-2 which supports the growth of itself & other T cells.

Also produce IL-4, IL-5 & IL-6 which stimulates the growth & differentiation of B cells into

- Plasma cells & Memory B cells

KILLER CELLS

The killer T cells now begin shooting holes in host cells that have been infected by viruses.

B Cells

The antibodies released by the B cells bind to antigens on the surfaces of free-floating viruses. Besides making it easier for macrophages to destroy viruses, this binding signals blood components called complement to puncture holes in the viruses.

Finally, as the infection is brought under control, the activated T and B cells are turned off by suppressor T cells.

However, a few "memory cells" remain behind to respond quickly if the same virus attacks again.

4. B cell activation & differentiation4. B cell activation & differentiation

5. Ab production

Ab production follows a characteristic pattern consisting of :

1. Lag Phase – immediate stage following antigenic stimulus during which Ab is not detectable in the circulation.

2. Log Phase – steady rise in the titre of Abs.

3. Plateau or Steady Phase – equilibrium between Ab synthesis & its catabolism.

4. Decline Phase – catabolism exceeds production, fall in Ab titre.

Primary & Secondary ResponsePrimary Response

Initial contact with the Ag

Slow, sluggish & short lived.

Long lag phase.

Low titres of Ab, does not persist for long.

IgM – predominant.

Secondary Response Response to

subsequent exposure to the same Ag.

Prompt, powerful & prolonged.

Short or negligible lag phase.

Very high levels of Ab, lasts for long periods.

IgG - predominant

Phases

1. A single injection of an Ag helps in sensitising / priming the immunocompetent cells producing the particular Ab.

2. Subsequent injections of an Ag – Boosters – induce effective levels of Ab.

Hence multiple doses of non living vaccines are administered to achieve effective levels of immunity.

Phases

With live vaccines, a single dose is sufficient as multiplication of the organism will provide a continuous stimulus.

“Negative Phase” – when an Ag is injected into an animal already carrying the specific Ab in circulation, a temporary fall in the level of Ab occurs due to the combination of Ag with the Ab. It is then followed by a rise in Ab titre.

A B C

Negative phase

Cell Mediated Immunity

Refers to the specific immune responses that do not involve antibodies.

CMI response 1st described by Jenner in 1798.

1890 - Koch described the exaggerated cutaneous reaction of tuberculous guinea pigs to the I.D. injection of tubercle bacillus – Delayed hypersensitivity (DH).

DH- skin lesions appear 48-72 hrs after administration of the Ag.

Applications of CMI CMI participates in following

immunological functions :1. Delayed hypersensitivity.2. Immunity in infectious diseases

caused by obligate & facultative intracellular parasites

Bacteria – Mycobacteria, Listeria Fungi – Histoplasma, Blastomycetes Protozoa – Leishmania,Trypanosoma Viruses – Measles, Mumps

Applications of CMI

3. Transplantation immunity & graft-versus-host reaction.

4. Immunological surveillance & immunity against cancer.

5. Pathogenesis of certain autoimmune diseases

e.g. Thyroiditis

Cells involved in CMI

CD8+T cells - recognise antigenic peptides in association with MHC class I molecule on a target cell.

CD4+T cells - MHC class II restricted, secrete cytokines which help in the growth & differentiation of T lymphocytes.

Scheme of Immune response

against T cell dependent Ags

http://in.youtube.com/watch?v=4kNsYa20EJU&eurl=http://rufusrajadurai.wetpaint.com/page/3D+Medical+Animations?t=anon

Factors influencing Ab production

1. Genetic factors2. Age3. Nutritional status4. Route of administration of Ag & site of

injection5. Size & number of doses6. Multiple Ags7. Adjuvants8. Immunosuppressive agents9. Effect of antibody

1. Genetic Factors

Different individuals within a species show differences in immune response to the same Ag.

This is determined by the genetic differences.

Controlled by the gene Ir.

2. Age

Embryo – immunologically immature - the developing lymphoid cells come into contact with all the tissue Ags of the body – Self Tolerance.

Up to 3-6 mths of age – protection provided by maternal Abs.

B cell responses to most protein Ags develop early.

Responses to polysaccharides & other Ags develop later, by 2 years of age.

3. Nutritional Status

Protein calorie malnutrition – suppress humoral as well as cell mediated immunity.

Deficiency of amino acids & vitamins – decrease in Ab synthesis.

4. Site & Route of Administration of Ag

Parenteral – better humoral response. Influence the type of Ig produced : Oral / Nasal – Ig A Inhalation of pollens – Ig E Parenteral administration of Ags – Ig G

Site of administration – relevant with some Ags Hepatitis B vaccine – deltoid (highly

immunogenic) - gluteal (less: paucity of APCs in gluteal fat – delays Ag presentation)

5. Size & Number of Doses Ag is effective only above a

minimum critical dose. Low dose – fails to induce immune response. High dose – develops tolerance. - do not respond to

subsequent doses of same Ag.

Multiple Ags

When 2 or more Ags are administered simultaneously, the effects may vary ;

Abs produced against different Ags just as though they had been given separately.

e.g. When 2 bacterial vaccines (typhoid & cholera) are given in a mixed form, the Ab response of one is not influenced by the other.

Multiple Ags

Ab response to one or the other Ag may be enhanced or diminished.

e.g. When toxoids are given with bacterial vaccines (DPT), the response to toxoid is enhanced.

When 2 toxoids (DT) given together with one in excess, response to other is inhibited.

Adjuvants

Any substance that enhances the immunogenicity of an Ag.

e.g. aluminium hydroxide

Increase the concentration and persistence of circulating antibody by:

1. Increasing the size of Ag - promotes phagocytosis & presentation by macrophages.

2. Stimulating the influx of macrophages & other immune cell types to the injection site.

3. Promoting local cytokine production

Types of Adjuvants Freund’s incomplete adjuvant : water-in-

oil emulsion with protein Ags in water phase.

Freund’s complete adjuvant : incomplete adjuvant along with a suspension of tubercle bacilli.

Repository adjuvants – aluminium hydroxide or phosphate.

Gram negative bacilli (lipopolysaccharide fraction) – Bordetella pertussis – acts as an adjuvant for diphtheria & tetanus toxoid in DPT vaccine.

Immunosuppressive Agents Inhibit immune response – useful in

transplantation procedure to prevent graft rejection.

e.g.corticosteroids,antimetabolites, cyclosporine

Corticosteroids – depletion of lymphocytes -inhibits histamine

release & inflammatory process

Cyclosporine –commonly used for immunosuppression

- selective inhibition of helper T cell activity

SUPERANTIGENS Class of bacterial toxins (staphylococcal

enterotoxins) & retroviral proteins that can activate very large number

of T cells irrespective of their antigenic specificities.

Features of super Ags :1. Not processed2. Interact with the MHC class II molecule

outside of the peptide - binding groove.

3. Bind only to the Vβ segment of TCR.

Monoclonal Antibodies (mAb)

Abs produced by a single clone of cell and directed against a single antigenic determinant are called Monoclonal Antibodies.

Very useful for diagnostic & research techniques.

Method for large scale production of mAb was developed by Kohler & Milstein in 1975.

Monoclonal Ab

Production is based on Hybridoma technology.

Hybridomas are somatic cell hybrids produced by fusing Ab forming spleen cells with myeloma cells.

It retains - Ab producing capacity of spleen cell. - ability to multiply indefinitely.

ADCC: Antibody Dependent Cell-mediated Cytotoxicity

Cytotoxic response is mediated by cells in the presence of Ab.

Cells carry receptor for the Fc portion of Ig – able to bind Ab coated targets.

Such cells are also referred to as Killer cells.

* In the absence of Ab, the same cell could destroy the target by natural killing – NK cells.

e.g. Eosinophils are very efficient mediators of ADCC against parasitic worms.

IMMUNOLOGICAL TOLERANCE

STATE OF SPECIFIC IMMUNOLOGIC UNRESPONSIVNESS TO A PARTICULAR Ag TO WHICH A PERSON HAS BEEN EXPOSED EARLIER.

Self Ag Embryonic life

TRANSFER FACTOR

Transfer of cell mediated immunity Nucleopeptide Non antigenic Stimulate release of lymphokines

from sensitised T cells Used in CMI deficiency-TB,

Lepromatus leprosy,MELANOMA,Wiskott-Aldrich syndrome

Theories of Immune Response

Side Chain Theory – Ehrlich (1900) Abandoned - Landsteiner demonstrated

that Abs can be formed against natural Ags as well as synthetic chemicals.

Direct Template Theory Ag act as a template for Ab synthesis. Indirect Template Theory – Burnet &

Fenner (1949) Entry of an Ag - Incorporation of some

of the genes from the antigenic determinant into the genome of Ab producing cells - Heritable changes occur in Ab producing cell

Theories Natural Selection Theory – Jerne

(1955)1. Embryonic life – formation of a

million diff. Abs (covers full range of Ags) – Natural Abs.

2. Entry of an Ag – selective combination with Ab having complementary fit – natural selection of cells forming that particular Ab.

Theories Clonal Selection Theory – Burnet (1957)1. During immunological development,

cells capable of reacting with different Ags are formed by somatic mutation.

2. Clone of cells having reactivity against self Ags - eliminated – called forbidden clones

3. Persistence of forbidden clones or redevelopment in later life – Autoimmunity

* most widely accepted theory

CYTOKINES Biologically active substances

(intercellular messengers) which are – produced transiently - exert their effects at very low (10–15)

conc. & - regulate immunological, inflammatory &

reparative host responses.

Includes – Interleukin (product of leucocytes)

- Interferons - Growth factors & others

Features of Cytokines Mediate their actions by binding to specific

cell- surface receptors. Produced by wide variety of cells like

lymphocytes, macrophages, platelets & fibroblasts.

Cytokines can have 1.Paracrine effect – act locally near the

producing cells 2.Autocrine effect – act directly on the

producing cells 3.Pleiotropic effect – multiple effects on

growth & differentiation of various cell types.

Cytokines: Source & Function

CytokineCytokiness

Source : Immune cellsSource : Immune cells Effects of CytokinesEffects of Cytokines

IL-1IL-1 Monocytes, Monocytes, macrophagesmacrophages

Activation of T & B cellsActivation of T & B cells

IL-2IL-2 T cellsT cells Proliferation and/or activation Proliferation and/or activation of T & B cellsof T & B cells

IL-4IL-4 T & B cells, mast cells,T & B cells, mast cells, Activation of B cells, Activation of B cells, differentiation of Th2 cellsdifferentiation of Th2 cells

IL-6IL-6 T cells, macrophagesT cells, macrophages Differentiation of T & B cellsDifferentiation of T & B cells

IL-10IL-10 T & B cells, T & B cells, macrophagesmacrophages

Suppression of macrophages, Suppression of macrophages, activation of B cellsactivation of B cells

IL-12IL-12 B cells, macrophagesB cells, macrophages Differentiation of Th1 cellsDifferentiation of Th1 cells

IFN IFN LeucocytesLeucocytes Antiviral activityAntiviral activity

IFN IFN FibroblastsFibroblasts

IFN IFN T cellsT cells

THANK U