Specific Immune Defense

Antigens Antibody-generator, Non-self, Large molecules Properties: ◦1. Immunogenicity ◦2. Reactivity Antigenic determinant or epitope Haptens

Specific Immunologic tolerance MHC Proteins – each individual has a different set of MHC proteins (except identical twins/clones) – indicate self vs. non-self Why do immune cells not attack “self”? Immune cells that would attack self are destroyed in thymus before birth

Overview of the cells of the Specific Immune Response Lymphocytes Immunocompetent = ready to engage in immune response B lymphocytes – produce antibodies ◦Mature in bone marrow ◦Surface receptors recognize antigen determinants T lymphocytes – lyse infected or abnormal cells through direct cell-to-cell contact ◦Mature in thymus ◦Surface receptors depend on Class I and Class II MHC proteins (MHC-antigen complex)

Cell-mediated Immunity Dendritic cells or Macrophages (APCs) – move to lymph nodes Helper T Cells Cytotoxic T Cells – only attack cells with same MHC proteins as self 1.APCs present antigen 2.Helper T Cells bind to MHC-antigen complex and are activated 3.Helper T cells go into mitotic phase and copy themselves – most are Effector Helper T Cells but some are Memory T cells (distribute throughout body and remain in tissue) 4.Effector Helper T Cells secrete Interleukins (stimulate Cytotoxic T cells and B cells) 5.Effector Cytotoxic T cells recognize infected cells with MHC-antigen complex, release perforans and destroy cell.

Cytotoxic T Cell

Humoral Immunity B Cells – activated by cytokines released by Helper T Cells Plasma Cells – antibody secreting cells Memory B cells – dormant cell Antibodies 1. Cytokines released by Helper T Cells activate B Cells. 2. APC (or sometimes just antigen itself) binds to B Cell receptors. 3. B Cell proliferates and differentiates into Plasma Cells and Memory Cells. 4. Plasma Cells secrete antibodies which bind to antigens 5. Memory Cells can respond rapidly to a second infection from same pathogen.

Antibody Structure and Function Antibody and antigen = lock and key Variable region leads to highly specific antigen binding site ◦Result of gene rearrangement (somatic recombination) Possible effects: ◦Viral inhibition ◦Neutralizing toxins (mask the toxicity) ◦Opsonization of phagocytosis ◦Agglutination (clumping) ◦Precipitation for soluble antigens ◦Signals the Classical Pathway of complement

Types of Antibodies Immunoglobulin – another name for antibody *IgG in plasma and tissue – effective against bacteria, viruses, and toxins and activates complement. ~80% of antibody content Involved in secondary antibody response Maternal antibody – lasts~6 months *IgA in breast milk, tears, nasal fluid, bile, urine *IgM develops in plasma and activates complement Involved in primary antibody response IgD on surfaces of B cells IgE associated with allergic reactions *most abundant

Complement System – Classical Pathway

Secondary Antibody Response Memory B cells remain in lymphoid tissues If come into contact with antigen (and pathogen) again ◦Divide and mature  plasma cells ◦Produce antibodies ◦Neutralization of pathogen (usually without symptoms)

Questions?

Possible Questions – difference between Cytotoxic T cells and Natural Killer Cells

Possible Questions – evasion of virus or cancer from cytotoxicity