immuno

Immunopharmacology

• Introduction-- Immune System

  • Defenses against antigenic insults:

    • Innate immune system

    • Adaptive immune system

• Innate Immune System:

  • Physical (skin)

  • Biochemical (e.g. complement, lysozyme)

  • Cellular (e.g. macrophages, neutrophils)

  • When the barrier is disrupted, bacterial destruction may occur by:

    • Lysozyme enzyme activity causes peptidoglycan cell wall component cleavage; also:

    • Split products from complement activation

      • Complement components: enhance macrophage and neutrophil phagocytosis by:

        • Acting as opsonins (C3b)

        • Attracting immunocytes to inflammatory sites (C3a, C5a)

        • Promoting bacterial lysis -- membrane attack complex generation

• Adaptive Immune System:

  • The adaptive immune system comes into play if the innate immune system has not managed the infection adequately.

  • Characteristics of the adaptive immune system:

    • Specific responses to a variety managements

    • Discriminate between foreign ("nonself") and "self", i.e. host antigens

    • Exhibits "memory"; initiates an aggressive response to previously encountered antigen

  • Effectors of humoral immunity: antibodies

  • Effectors of cell mediated immunity: activated lymphocytes

  • Specific Immunity:-- requirements

    • Antigen presenting cells (APCs)

      • Langerhans cells

      • B lymphocytes

      • Dendritic cells

      • Macrophages

    • APCs digest antigens (enzymatically) producing peptides that:

      • Interact with T cell lymphocyte receptors (TCR) in association with class I and class II major histocompatibility complex proteins (MHC proteins)

      • T cell lymphocyte activation-- additional molecular dependencies:

        • CD₄ on helper T cells

        • CD₈ on cytotoxic T cells

        • LFA-1(lymphocyte functional antigen) and CD₂ on both helper and cytotoxic T cells

        • Co-stimulatory molecules (B7.1 and B7.2) by cognate receptors on APCs

  • Lymphocyte selection:

    • Thymic lymphocyte that bind to "self"-- eliminated by apotosis (negative selection)

    • Thymic lymphocytes that respond to foreign antigens in the presence of "self" MHC: retained (positive selection) and distributed to peripheral sites, available for later activation (after interacting with MHC-presented peptides):

      • Lymph node

      • Spleen

      • Peripheral blood

      • Musosa-associated lymphoid tissue

  • Subsets of T helper lymphocytes--discrimination based on cytokine secretion, after activation

    • TH1--Cell-mediated Immunity

• "Function of T helper cells: Antigen-presenting cells (APCs) present antigen on their Class II MHC molecules (MHC2). Helper T cells recognize these, with the help of their expression of CD4 co-receptor (CD4+). The activation of a resting helper T cell causes it to release cytokines and other stimulatory signals (green arrows) that stimulate the activity of macrophages, killer T cells and B cells, the latter producing antibodies."

• Figure: Haggstrom M T helper cell function: http://en.wikipedia.org/wiki/File:Lymphocyte_activation_simple.png

• Figure Legend: http://en.wikipedia.org/wiki/Immune_system

• • • • Produces interferon-g (IFNg)

      • Produces interleukin-2 (IL-2)

      • Produces tumor necrosis factor-b (TNFb)

      • Induces cell-mediated immunity by activation of:

        • Cytotoxic T cells (CTL)

        • Natural killer (NK) cells

        • Macrophages

    • TH2 -- Humoral Immunity

      • Produces (interleukins) IL-4, IL-5, IL-6 which in turn causes:

        • B-cell proliferation

        • Differentiation into antibody secreting plasma cells

  • T helper lymphocytes --mutual regulation:

    • TH2 cells produce IL-10: inhibits TH1 cytokine production (down-regulates MHC expression by APCs)

    • TH1 interferon-g: inhibits TH2 cell proliferation

  • Other down-regulation/suppression factors (in some tissues)

    • Iransforming growth factor-b (TGF-b)

      • Down-regulates lymphocyte proliferation

    • Prostaglandin E2: down-regulates immune response

  • T helper lymphocytes: phenotype selection based on antigenic challenge

    • Extracellular bacteria: TH2 cytokine release

    • Intracellular organisms (e.g. Mycobacterium): TH1 cytokine release

Cytotoxic Consequences of Immune System Activation

• Activated cytotoxic T cells (recognize processed peptides presented by virus-infected cells/tumor cells)

  • Induce target cell death by:

    • Perforin

    • Lytic granule enzymes ("granzymes")

    • Fas-Fas ligand (Fas-Fasl) apotosis pathway

    • Nitric oxide (may be released): inhibits cell enzymes

• Viral Antigen Presentation (by virus-infected cells):

  • Nonapeptide fragments in the group of class 1 MHC molecules

• MHC molecules

  • Class I MHC molecules: presenting fragments of cellular antigens (virus/tumor antigens)--after Golgi apparatus processing

  • Class II MHC molecules: presenting antigen fragments from:

    • Internalized/enzymatically digested foreign antigens

• Natural Killer Cells: (NK): (CD16+, CD56+, CD57+)--possible role in tumor rejection/viral immunity; in vivo role uncertain

  • NK cells: large granular lymphocytes

    • Azurophilic cytoplasmic granules

    • Surface immunoglobulin negative

    • FC receptor-positive

    • Probably separate lymphoid cell lineage

  • NK cells: main precursor of lymphokine activated killer (LAK.)cells

    • LAK cells:

      • Stimulated by IL-2 (high concentration)

      • Referred to as (promiscuous killers) because:

        • Kill across MHC barriers

        • Kill target cells not expressing MHC

B lymphocytes: Humoral Immunity

Hypersensitivity

Classification: determined by time required for expression of clinical symptoms following antigen exposure: Immediate, Delayed

Immediate Hypersensitivity

• Immediate Hypersensitivity: antibody mediated; symptoms occurring within minutes to a few hours following antigen exposure -- Three Categories:

  • Type I:

    • Characteristics type I:

      • Antigen cross-linking of membrane-bound IgE on blood basophils or tissue mast cells

    • Consequences type I:

      • Cellular Degranulation: releasing histamine, leukotrienes, and other mediators)

      • These mediators may induce:

        • Asthma

• "The hyper-reactive bronchioles in cases of asthma usually exhibit bronchiolar smooth muscle hypertrophy.

  • This is simply because these muscles get a lot of "exercise", as they contract in response to allergens."

• Ó 1999 KUMC Pathology and the University of Kansas, used with permission; courtesy of Dr. James Fishback, Department of Pathology, University of Kansas Medical Center.

• • • • • Hives

        • Hay fever

  • Type II:

    • Characteristics-type II:

      • Antigen-antibody complex formation between foreign antigen +IgM or IgG immunoglobulins

      • Examples:

        • Hashimoto's thyroiditis-slide A

• "This image was made by the use of a goat antisera, tagged with fluorescein, made against human IgG to detect human autoantibodies bound to the thyroid tissue.

• The thyroid follicular epithelial cells are staining."

• ©1999 KUMC Pathology and the University of Kansas, used with permission; courtesy of Dr. James Fishback, Department of Pathology, University of Kansas Medical Center.

• • • • • Hashimoto's thyroiditis-slide B

• "This image was made by the use of a goat antisera, tagged with fluorescein, made against human IgG to detect human autoantibodies bound to the thyroid tissue.

• In this case, anti-thyroglobulin antibody is detected.

• The thyroid follicle colloid is stained positively."

• ©1999 KUMC Pathology and the University of Kansas, used with permission; courtesy of Dr. James Fishback, Department of Pathology, University of Kansas Medical Center.

• • • Occurrence-type II:

      • Blood transfusion reactions

      • Newborn: hemolytic disease

        • Mechanism:

          1. Antibodies formed «foreign erythrocyte membrane antigens

      • Drug Induced

    • Consequences-type II:

      • Complement cascade activation

      • Generation of membrane attack complex ® destroys red blood cells

    • Newborn hemolytic disease:

      • Anti-Rh IgG antibodies (produced by an Rh negative mother):

        • Cross the placenta

        • Bind to erythrocytes of Rh-positive fetus;damage fetal erythrocytes

      • Prevention:

        • Administration of anti-Rh antibodies to the mother; 24-48 hours after delivery of the first Rh+ child

    • Drug Induced: Examples --

      • Penicillin administration to allergic patients

        • Mechanism: penicillin binds to erythrocytes or other host tissue leading to neoantigen production of antibodies followed by induction complement-mediated cell lysis

        • Repeat administration may causesystemic anaphylaxis

  • Type III:

    • Characteristics-type III:

      • Presence of increased antigen-antibody complex concentrations may lead to tissue damage

      • Example: polyarteritis

• "Polyarteritis affects small to medium-sized arteries.

  • Associated with hepatitis B, and circulating immune complexes are thought to play a role, although, like many immunologic diseases, this remains speculative.

  • Clinically, any artery can be affected, and thrombosis may occur.

  • Symptoms are related to the organ involved, although patients also have constitutional symptoms, like malaise, fever, and weight loss.

  • Histologically, fibrinoid necrosis is prominent, with a variable perivascular infiltrate of lymphocytes and polymorphs. "

• © 1999 KUMC Pathology and the University of Kansas, used with permission; courtesy of Dr. James Fishback, Department of Pathology, University of Kansas Medical Center.

• • • • Complexes activate complement producing components with:

        • Anaphylatoxic / chemotactic actions (C5a, C3a, C4a) which:

          1. Increase vascular permeability

          2. Attract neutrophils to the site of complex deposition

             • Complex deposition; neutrophil-release of lytic enzymes may cause:

               1. Skin rash

               2. Glomerulonephritis

               3. Arthritis

Delayed Hypersensitivity

• Cell-mediated;

• Responses: 2-3 days after sensitizing antigen exposure

• Tissue Characteristics:

  • Local inflammatory response

  • Significant damage associated with influx of antigen-nonspecific inflammatory cells especially neutrophils and macrophages

• Macrophage/Neutrophil Recruitment -- mediation:

  • TH1-produced cytokines cause:

    1. Extravasation and chemotaxis of neutrophils and circulating monocytes

    2. Induction of myelopoiesis

    3. Macrophage activation causing enhanced:

       • Phagocytic

       • Microbicidal activity

       • Antigen-presenting functions

       • Eigestive enzyme release, contributing to extensive tissue damage

• Delayed-type hypersensitivity however are very effective in combating/eliminating infections caused by intracellular pathogens:

  • M. tuberculosis

  • Leishmania

Autoimmunity

• Introduction

  • Failure to distinguish "self" tissues and cells from foreign ("nonself") antigens

  • Caused by activation of self-reactive T and B lymphocytes which induce:

    • Cell-mediated responses against self antigens

    • Humoral immune responses against self antigens

• Clinical Pathologic Consequences, Autoimmune Disease:Examples --

  • Rheumatoid arthritis

    • IgM antibodies (rheumatoid factors) react with Fc IgG component to form immune complexes.

      • Immune complexes ®split complement components ® joint and kidney inflammation

  • Systemic lupus erythematosus

• The so-called "butterfly" rash of lupus is typical.

• It is erythematous, and extends in butterfly fashion over both sides of the face.

• It is not seen so often nowadays, since physicians are quick to prescribe systemic steroids.

• The rash is made worse by exposure to sunlight."

• Ó 1999 KUMC Pathology and the University of Kansas, used with permission; courtesy of Dr. James Fishback, Department of Pathology, University of Kansas Medical Center.

• • • Antibodies produced against:

      • Self DNA

      • Red blood cells

      • Platelets

      • Histones

  • Insulin-dependent diabetes mellitus

• "Lymphocytic infiltrates in islets (T-cells)."

• © 1999 KUMC Pathology and the University of Kansas, used with permission; courtesy of Dr. James Fishback, Department of Pathology, University of Kansas Medical Center."

• • • Cell-mediated

      • Insulin-producing pancreatic B cells

    • Activated CD4+ T_DTH :

      • Infiltrate islets of Langerhans

      • Recognize self islet B-cell peptides

    • Possible Explanations for Autoimmune Disease:

      • Self-reactive T cell exposure to previously unseen antigens (e.g. myelin basic protein, lens protein)

      • Molecular mimicry in which immune responses are directed against pathogenic antigenic determinants sharing identical or very similar epitopes with normal host tissue -- example:

        • Rheumatic fever following Streptococcus pyrogenes infection-- heart muscle damage secondary to host-immune responses against streptococcal antigenic determinants shared with myocardial tissue

        • In the case of viral etiology -- cell-mediated and humoral immune responses are directed against viral epitopes mimicking sequestered self antigens

      • Inappropriate class II MHC molecular expression on cell membranes that should not and normally do not expressed class II MHC (pancreatic islet B cells)

        • B cells then present "self" peptides to helper T cells ® induce CTL, T_DTH, and B lymphocyte cells ® react against self antigens

Antibodies as Immunosuppressive Drugs

• Overview

  • Increased antibody purity/specificity used for immunosuppression due to:

    • Hybridoma method -- fusing antibody-forming cells to immortal plasmacytoma cells

    • Allows for mass culture antibody production

• Antilymphocyte and Antithymocyte Antibodies

  • Antisera against lymphocytes -- heterologous antilymphocyte globulin (ALG)

  • Organ transplantation programs use:

    • Antilymphocyte globulin (ALG)

    • Antithymocyte globulin (ATG)

    • Monoclonal anti-T cell antibodies

• Antilymphocyte antibodies:

  • Act on small, long-lived peripheral lymphocytes (circulating between lymph and blood)

  • Continued administration: depletion of:

    • "Thymus-dependent" lymphocytes from lymphoid follicle cuffs

  • Mechanism:

    • Antilymphocyte antibodies bind to T-cell surface

    • Induced immunosuppression

    • Opsonization + phagocytosis of antibody-bound cells: hepatic mediation

    • Cytotoxic destruction of antibody-bound cells: spleen-mediated (serum complement involvement) for poly clonal preparations

    • Antibody binding may also block immune function by:

      • Altering membrane surface expression of molecules important for lymphocyte function

      • Example: monoclonal antibody against CD3-T cell receptor complex.

  • Consequences of destruction/inactivation of T cells:

    • Degradation of delayed hypersensitivity and cellular immunity

    • Humoral antibody formation: intact

    • Antibodies (polyclonal/monoclonal) -- most selective means of modulating immune response;

      • Particularly important in organ transplantation

• Management of Transplantation

  • ALG + monoclonal antibodies:

    • Useful in treating initial rejection by inducing immunosuppression

    • Useful in treating steroid-resistant immunorejection

  • ALG- usually administered with prednisone + azathioprine

  • ALG plus monoclonal antibodies:

    • Used early following kidney transplantation in order to avoid early use of cyclosporine (enhanced cyclosporine- nephrotoxicity when used immediately after transplantation)

  • ALG: also used in recipient preparation for bone marrow transplant

    • Large dose ALG 7-10 days before transplant

    • Residual ALG: kills T cells in the donor-marrow-graft

      • Reduction in likelihood of severe graft-versus-host syndrome

• ALG: adverse effects

  • Injection site: local pain/erythema

  • Anaphylactic/serum sickness reactions

  • Histiocytic lymphoma in the buttock (site of ALG injection)

  • Increased cancer incidence and kidney transplant patients (2% in long-term survivors)

    • May be secondary to immunosuppression against oncogenic viruses

• Clinical Trials/Special Uses:

  • Murine (mouse) monoclonal antibody (OKT3) -- directed against CD3+ on human thymocyte and T cell surfaces may help manage renal transplant rejection

    • OKT3: marketed for renal allograph rejection crisis

  • Ricin-conjugated murine monoclonal antibody -- ongoing clinical trials:

    • Apparently potent in reversing graft-versus-host syndrome after allogenic bone marrow transplantation

• Immune Globulin Intravenous (IGIV)

  • Intravenous use: polyclonal human immunoglobulin

  • No specific antigen target

  • Immunoglobulin preparation: derived from thousands of healthy individuals

  • Expectation: a "normalizing" effects on patient's immune system

  • Clinical Applications:

    • Asthma

    • Autoimmune disorders

    • Kawasaki syndrome

      • Reduces systemic inflammation

      • Prevents coronary artery aneurysms

    • Subacute lupus erythematosus

    • Refractory idiopathic thrombocytopenic purpura

  • Suggested Mechanisms:IGIV

    • ¯ Reduction of helper T cells

    • ­ Increase in suppressor T cells

    • ¯ Reduced immunoglobulin production

    • ¯ Reduced idiotypic-idiotypic interaction with "pathologic antibodies"

• Rh_o(D) immune globulin micro-dose

  • Prevention of Rh hemolytic disease of the newborn

  • Rationale:

    1. A primary antibody response to a foreign antigen; blocked if the specific antibody to that antigen is administered passively at the time of antigen exposure

  • Composition: Rh_o(D) immune globulin:

    1. Concentrated solution (15%) of human IgG with a higher titer of antibodies against the Rh_o(D) red cell antigen

  • Process leading to Rh hemolytic disease in the newborn:

    1. Rh-negative mothers are sensitized to the D antigen at birth of Rh_o(D)-positive or D^u-positive infants (fetal red cell's may leak into the mother's bloodstream.

       • Sensitization may also occur with miscarriages/ectopic pregnancies

    2. Subsequent pregnancies: maternal antibody against Rh-positive cells ® to the fetus during the third trimester ®erythroblastosis fetalis -- hemolytic disease of the newborn

    3. Upon Rh_o(D)-administration to the mother within three days after the birth of Rh-positive baby, the mother's own antibody responds to the foreign Rh_o(D)-positive cells will be suppressed

       • Following this treatment: Rh hemolytic disease has not been reported to occur in subsequent pregnancies.

       • Successful prophylaxis requires:

         1. Mother must be Rh_o(D)-negative

         2. Mother must be D^u-negative

         3. Mother must not be already immunized to Rh_o(D) factor