Adaptive Immunity: Specific Defenses of the Host

Transcription

1 PowerPoint Lecture Presentations prepared by Bradley W. Christian, McLennan Community College C H A P T E R 17 Adaptive Immunity: Specific Defenses of the Host

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3 The Adaptive Immune System Adaptive immunity: defenses that target a specific pathogen Acquired through infection or vaccination Primary response: first time the immune system combats a particular foreign substance Secondary response: later interactions with the same foreign substance; faster and more effective due to "memory"

4 The Immune Response Three Key Features 1. Recognition of self 2. Specificity 3. Memory

5 Anatomy of the Immune System Blind-ended capillaries in tissues collect lymph and cells and drain to vena cava Lymph nodes filter the lymph

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7 Anatomy of the Immune System Bone marrow and thymus are primary lymphoid organs Lymph nodes and spleen are secondary lymphoid organs

8 Figure 17.1 Differentiation of T cells and B cells. Stem cells develop in bone marrow or in fetal liver Red bone marrow of adults Stem cell (diverges into two cell lines) Thymus Differentiate to B cells in adult red bone marrow Differentiate to T cells in thymus B cell T cell Migrate to lymphoid tissue such as spleen, but especially lymph nodes

9 Humoral Immunity Protection by antibody (Ab) molecules Soluble proteins Produced by B lymphocytes which differentiate to plasma cells Identify and bind to antigens

10 Cell-Mediated Immunity Protection by T lymphocytes that react to cellular antigen Specialized cells that act by a variety of non-phagocytic mechanisms Respond to infected, cancerous, and foreign cells

11 Antigen Foreign substance that stimulates the immune system Almost always protein Antigen (Ag) means antibody generating

12 Antibodies Also called immunoglobulins (Ig) Structure: 2 pairs of identical polypeptide chains Y -shaped molecule with 2 binding sites Five classes of Ig (IgG,IgM,IgA, IgD, IgE)

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14 Antibody Function Identification molecule no direct activity Agglutination Opsonization Activate complement (C ) Neutralize soluble proteins and virus

15 Figure Overview (1 of 6)

16 Figure Overview

17 Antigens Antigens: substances that cause the production of antibodies Usually components of invading microbes or foreign substances Antibodies interact with epitopes, or antigenic determinants, on the antigen Haptens: antigens too small to provoke immune responses; attach to carrier molecules

18 Figure 17.2 Epitopes (antigenic determinants). Antibody A Epitopes (antigenic determinants) on antigen Binding sites Antigens: components of cell wall Bacterial cell Antibody B

19 Figure 17.3 Haptens.

20 Table 17.1 A Summary of Immunoglobulin Classes

21 Clonal Selection of Antibody-Producing Cells Major histocompatibility complex (MHC) genes encode molecules on the cell surface Class I MHC are on the membrane of nucleated animal cells Identify "self" Class II MHC are on the surface of antigen-presenting cells (APCs), including B cells

22 B Cells Proliferate in response to Ag and a co-stimulatory signal Differentiate to antibodyproducing plasma cells and memory cells Memory cells respond to Ag much faster than virgin B cells

23 T Cell Help Most B cells only respond to Ag with the help of Ag-specific T cells Some B cells do not require T cell help to make responses to Ag

24 Clonal Selection of Antibody-Producing Cells T-dependent antigen Antigen that requires a T H cell to produce antibodies T-independent antigens Stimulate the B cell without the help of T cells Provoke a weak immune response, usually producing IgM No memory cells generated

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28 Clonal Selection of Antibody-Producing Cells Clonal selection differentiates activated B cells into: Antibody-producing plasma cells Memory cells Clonal deletion eliminates harmful B cells

29 Antibody Diversity In humans, maybe as many as different B cells Genes for these are formed through rearrangements of the germline DNA and later modified by mutational events