Unit Six: Blood Cells, Immunity, and Blood Coagulation Chapter 34: Resistance of the Body to Infection. II. Immunity and Allergy Innate Immunity Guyton and Hall, Textbook of Medical Physiology, 12th edition

Innate Immunity Innate Immunity Phagocytosis of bacteria and other invaders by wbcs and cells of the tissue macrophage system Destruction of swallowed organisms by stomach acid and digestive enzymes Resistance of the skin to invasion Presence of antibacterial chemicals (i.e. lysozyme, complement, NK cells, etc.)

Acquired (Adaptive) Immunity Basic Types Humoral or B-cell Immunity Cell-mediated or T-cell immunity Initiation of the Responses- antigens MW greater than 8000 Epitopes or antigenic determinants on surface Generally protein or large polysaccharides

Lymphocytes T and B Lymphocytes T lymphocytes migrate from the bone marrow to the thymus where they mature and are responsible for cell mediated immunity B lymphocytes are preprocessed in the liver, then the bone marrow and are responsible for antibody production The “B” designation originated from the bursa of Fabricius in the chicken.

Fig. 34.1 Formation of antibodies and sensitized lymphocytes from a lymph node in response to antigens

Lymphocytes (cont.) Preprocessing of the T Lymphocytes-occurs shortly before or just after birth In the thymus each T cell develops specificity against one antigen Continues until there are thousands of different T cells with specific reactivities against 1000s of antigens T cells then migrate to the secondary lymphoid tissues T cells capable of reacting against “self-antigens” are destroyed instead of being released

Lymphocytes (cont.) Preprocessing of the Lymphocytes Instead of the whole cell developing reactivity against the antigen, the B cells actively secrete antibodies that are the reactive agents Greater diversity than T cells: can form millions of types of antibodies with different specific reactivities T-Cells and B-Cell Antibodies React Highly Specifically Against Specific Antigens-Role of Lymphocyte Clones

Lymphocyte Clones Fig. 34.2

Lymphocyte Clones (cont.) Millions of specific types of lymphocytes are stored in the lymphoid tissues Origin of the many clones of lymphocytes Mechanism for activating a clone of lymphocytes Role of macrophages Role of the T cell in the activation of B cells

Humoral Immunity and the Antibodies Formation of Antibodies by Plasma Cells Formation of “Memory” Cells Difference Between Primary and Secondary Responses

Humoral Immunity and the Antibodies Fig. 34.3 Primary and secondary antibody responses

Antibodies (cont.) Nature of Antibodies Gamma globulins (immunoglobulins b. MW between 170,000 and 970,000 c. Make up 20% of all the plasma proteins d. Consist of heavy and light polypeptide chains e. Have variable and constant regions

Antibodies (cont.) Fig. 34.4 Structure of the typical IgG antibody

Antibodies (cont.) Specificity of Antibodies-each antibody is specific for a particular antigen Ka is the affinity constant and a measure of how tightly the antibody binds to the antigen

Blood, Lymph, B cell surface Cell bound to mast cells and basophils Antibodies (cont.) Classes of Antibodies Class Structure Location MW Half-Life In Serum Function IgG Monomer Blood, Lymph, Intestine 170,000 23 days Phagocytosis, neutralization, crosses placenta IgM Pentamer Blood, Lymph, B cell surface 970,000 5 days Primary response, phagocytosis, agglutination IgA Dimer Secretions 405,000 6 days Mucosal ab IgD B cell surface 175,000 3 days Surface Ig on B cells IgE Cell bound to mast cells and basophils 190,000 2 days Allergic Reactions,parasitic reactions

Antibodies (cont.) Mechanism of Action of Antibodies (Direct) Agglutination Precipitation Neutralization Lysis

Mechanism of Action of Antibodies (Indirect)-the Complement System Antibodies (cont.) Mechanism of Action of Antibodies (Indirect)-the Complement System Fig. 34.6

Antibodies (cont.) Classic Pathway Opsonization and phagocytosis Lysis Agglutination Neutralization of viruses Chemostaxis Activation of mast cells and basophils Inflammatory effects

Activated T Cells and Cell-Mediated Immunity Release of Activated T Cells From Lymphoid Tissue and Formation of Memory Cells APCs, MHC Proteins, and Antigen Receptors on T lymphocytes

Activated T Cells and CMI (cont.) Fig. 34.7 Activation of T cells requires interaction of T cell receptors with an antigen that is transported to the surface of the APC by a MHC protein.

Types of T Cells Helper T Cells—Role in Overall Regulation of Immunity Production of lymphokines (i.e. interleukins 2,3,4,5,6 and gamma interferon) Specific regulatory functions of the lymphokines Stimulation of growth and proliferation of cytotoxic T cells and suppressor T cells Stimulation of B cell growth and differentiation to form plasma cells and antibodies

Types of T Cells (cont.) Helper T Cells—Role in Overall Regulation of Immunity (cont.) e. Activation of the macrophage system f. Feedback stimulatory effect on the helper cells themselves

Types of T Cells (cont.) Fig. 34.8 Regulation of the immune system

Cytotoxic T Cells are “Killer” Cells Types of T Cells (cont.) Cytotoxic T Cells are “Killer” Cells Fig. 34.9 Direct destruction of an invading cell by sensitize T cytotoxic cells

Types of T Cells (cont.) Suppressor T Cells Can suppress the functions of both T helper and T cytotoxic cells Regulatory cells—prevent excessive immune reactions that might be damaging to the host

Tolerance Tolerance to One’s Own Tissues Results from Clone Selection During Preprocessing Failure Leads to Autoimmune Diseases Rheumatic fever Glomerulonephritis Myasthenia gravis Systemic lupus erythematosus (SLE)

Immunization Active Immunity Artificially acquired Naturally acquired Passive Immunity

Allergy and Hypersensitivity Type I Hypersensitivity (IgE antibody mediated) Anaphylaxis Urticaria Hay fever Mast cell involvement and histamine Type II Hypersensitivity (Cytotoxic reactions) Type III Hypersensitivity (Immune complex) Type IV Hypersensitivity (Delayed cell mediated)