Pathology: Immunology Study Case Questions And Correct Answers.

Immunogens and Antigens - correct answer Immunogen: A molecule that can elicit the production of an antibody when introduced into the host. Antigen: A molecule that is recognized and bound by an antibody. An immunogen must be an antigen, but an antigen is not necessarily an immunogen. Innate vs. Adaptive Immune System - correct answer 1) Adaptive takes time to react to pathogen; innate are always present and ready to be mobilized. 2) Adaptive is antigen specific; innate is not. 3) Adaptive displays immunological memory, remembering a pathogen and reacting quicker upon subsequent exposure; innate does not. 4) Adaptive has primarily lymphocytes, innate primarily phagocytes. Ways to Characterize Immunity - correct answer 1) Innate v. Adaptive 2) Location 3) Mechanism (soluble v. cellular) 4) Active v. Passive Barriers of Immune Defence - correct answer Considered part of innate immune defense. 1) Physical barriers: Epithelial tight junctions, flow of fluids like sweat, tears, saliva, urine, or mucus, and peristalsis of cilia. 2) Chemical Barriers: Fatty acids in sweat that inhibit bacterial growth, lysozymes in tears, saliva, and mucus, defensins in lung and GI tract, Surfactants in lung. 3) Microbiological: Cell-mediated, e.g. flora in skin and GI tract that prevent colonization of pathogenic bacteria. PAMPs and PRRs - correct answer Innate immunity cells recognize Pathogen Associated Molecular Patterns, PAMPs. The receptors for these are called non-clonal Pattern Recognition Receptors, PRRs. PRRs are limited in number, and recognize broad structural motifs that are found on families of microbes. They are germline encoded, and all innate immune cells will express the same ones. PRRs can recognize DAMPs as well, which are released from damaged or necrotic cells. TLRs - correct answer Toll-like receptors. An example of PRRs. When a PAMP binds to a TLR, it getnerates an inflammatory response involving phagocytic cells, and the generation of inflammatory cytokines. e.g. Bacterial Lipopolysccharides are found in gram-neg bacteria and binds TLR 4, while Peptidoglycans are part of gram-pos bacteria and are recognized by TLR 2. Types of PAMPs - correct answer 1) Lipopolysaccharides: All Gram neg 2) Unmethylated CpG: Bacterial DNA 3) Formylated peptides: Bacterial proteins 4) dsRNA: Viruses 5) Mannans: Yeast cell walls Other PRRs - correct answer 1) CLRs: C-Type lectin. Recognize cell wall components of bacteria/fungi. 2) RLRs: RIG-I-like receptors. Cytosolic, they recognize dsRNAs 3) NLRs: NOD-like. They recognize a number of structuraly unrelated intracellular PAMPs and DAMPs Innate Immune Fluid Phase/Soluble Defense Mech - correct answer 1) Interferons and defensins. Leukocytes and fibroblasts make interferons in response to viral infection, which cause an inflammatory response. Defensins made by many cells, and are antimicrobial. 2) Complement. Set of proteins made by liver, they circulate in blood inactive until activated by pathogens; they either directly kill pathogen or tag it to be phagocytosed. They also lead to increased vascular permeability, phagocyte recruitment. 3) Acute-Phase Proteins. Also made by liver. They tag pathogens for phagocytosis, and are involved in fibrinogen and binding iron to prevent bacterial growth. Cells of Innate Immune System - correct answer They will accumulate at sites of infection or injury and cause acute inflammation. 1) Polymorphonuclear leukocytes: come from Myeloblasts. Neutrophils, eosinophils, basophils. These will also make interferons in response to viral infections. 2) Mononuclear phagocytes: Come from monoblasts. Monocytes, macrophages. 3) Dendritic cells: Also come from monoblasts. Capture antigens, process and present them to T lymphocytes. They initiate T cell response. 4) Natural Killer Cells: Similar to monocyte, they release lytic granules that kill some virus-infected cells. They are lymphocytes, but have no T or B cell markers. Parts of Adaptive Immunity - correct answer 1) Humoral. Mediated by antibodies (a type of immunoglobulin) in blood, saliva, mucus, etc. Protects from extracellular infections (e.g. most bacteria). Antibodies will bind epitopes from antigens/immunogens. Immunity provided by antibodies can be transferred by serum to other body fluids (passive immunization). See Clonal Selection Hypothesis. 2) Cell-mediated. Requires direct participation of immunologically reactive cells, and is generally in response to intracellular (e.g. viral, some bacterial) infections. T cells contact MHCs on foreign peptides, proliferate and kill cells with MHC. Also generates memory cells. Cells of Adaptive Immunity - correct answer Two types of Lymphocytes: Both come from lymphoid progenitor cell. 1) B Lymphocytes. Antigen Receptor, BCR, is a membrane Immunoglobulin (mIg). They will differentiate into plasma cells, which have no receptors but make antibodies. Part of humoral response. 2) T Lymphocytes. Have T cell Antigen Receptor (TCR). Divided into TH, which have CD4, and TC, which have CD8. TH are helper cells that make cytokines; recognize MHC Class II. TC will diff into cytotoxic T cells, which can kill virally infected cells; recognize MHC Class I. Part of cell-mediated response. Clonal Selection Hypothesis - correct answer 1) During Development, progenitor cells in bone marrow or thymus will make a large number of B/T lymphocytes with different specificities. 2) During infection, the lymphocytes with receptors that recognize the pathogen are activated. 3) This results in proliferation and differentiation of that lymphocyte, which terminate infection. Some become plasma cells, others become memory cells. These steps occur in adaptive humoral immunity. Characteristics of Adaptive Immunity - correct answer 1) Antigen Specificity 2) Diversity (Lymphocyte repertoire) 3) Immunologic Memory. The secondary response is more rapid due to memory lymphocytes. 4) Non-reactivity to self. Immature immune cells are killed if they encounter antigens. Communication between Innate and Adaptive - correct answer 1) Innate Immunity cellular response, e.g. phagocytes, NK cells, etc., will make cytokines. Cytokines will stimulate B and T cells to respond. 2) Adaptive Immunity Response, e.g. B and T cells, will make antibodies and cytokines, both of which stimulate innate immunity cellular response. Primary Lymphoid Organs - correct answer Site of generation of immune cells. Includes Bone Marrow, which is the origin of all immune cells, and the Thymus, which contains emigrants from bone marrow and serves as site where T cells discriminate self from nonself. Secondary Lymphoid Organs - correct answer Areas where immune response initiated. Include: Lymph nodes, spleen, MALTs (lymphocytic infiltrations). 1) Lymphocytes encounter antigen, activate, undergo clonal expansion, and differentiate into effector cells. 2) B cells further mature in germinal centers