Types of Immune Responses Types of Immune Responses innate response not specific to a type of immunological challenge represents the immune response which does not have memory e.g., anatomic barriers (skin), inflammation, complement cascade recognizes structures common to multiple microbes found in nearly all forms of life cells include natural killer cells mast cells eosinophils basophils phagocytic cells (macrophages, neutrophils, and dendritic cells) acquired response portion of immune response which has memory occurs in a pathogen and antigen specific mechanism requires antigen processing and presentation performed by antigen presentation cells (APC) B cells and dendritic cells are two examples of APCs the APC breaks down the protein antigen in a multitude of enzymatic reactions and presents key peptide sequences via the major histocompatibility complex (MHC) receptors once presented on the surface of the APC, the T-cell receptor recognizes the MHC/antigen complex prior to T-cell activation cells include CD8+ T lymphocytes T helper cells delta gamma T cells B cells and plasma cells Types of Immunological Reactions Type I: Immediate anaphylactic reaction associated with allergy mediated by IgE antibody activation of mast cells and basophils Type II: Antibody dependent (aka cytotoxic) hypersensitivity mediated by IgG and IgM antibodies Type III: Immune complex (antigen bound to antibody) deposition type of hypersensitivity mediated by IgG and IgM antibodies which when bound to antigen get deposited in various tissues Type IV: Delayed-type or cell-mediated hypersensitivity mediated by T cells, monocytes and macrophages take several days to develop examples include tuberculosis skin test topical antibiotic ointment the immune response to metallic orthopaedic implants is typically a Type IV (delayed-type hypersensitivity reaction) Immunoglobulins Immunoglobulin types IgG the most abundant immunoglobulin IgM the first class of antibody to appear in our serum after exposure to an antigen IgA the major class of antibody in external secretions (e.g. intestinal mucus, bronchial mucus, saliva, and tears) IgE important in conferring protection against parasites and allergic reactions Immunologic Variations Benign Ethnic Neutropenia Most common neutropenia in the world Approximately 25%-50% of people of African descent and some sub-groups in the Middle East found to have low ANC without increased infection risk ANC < 1.5 x 10(9) cells/L considered "abnormally low" without clear clinical relevance. 4.5% African Americans, 0.79% white Americans, 0.38% Mexican-Americans below this ANC Also more common in males vs females, athlete vs non-athlete, and children under age 5