Immunology and Serology - 04 Biology of Immune Response

IMMUNOLOGY AND SEROLOGY BIOLOGY OF THE IMMUNE RESPONSE OUTLINE • Phases of Immune Response • Assays of Immune o Types of Specific Competence Immunologic Reactions o Enumeration and Functional o Humoral Immune Response Assays of T Cells o Cellular Immunity o Enumeration and Functional o Cytokine Storm Assays of B Cells o Phagocytosis PHASES OF IMMUNE RESPONSE TYPES OF SPECIFIC IMMUNOLOGIC REACTIONS • Adaptive can be cell-mediated (cellular) and antibodymediated (humoral) CELLULAR IMMUNITY • • • • • Cellular (Cell-mediated) immunity - action of T cells Process of Cellular immunity o Antigen enters the body and macrophage engulfs & process antigen o Antigen presented by macrophages will not be recognized by T cell unless there is presence of HLA Class I/II ▪ CD8+ T cell - requires HLA Class I ▪ CD4+ T cell - requires HLA Class II o After presentation to antigen and activation, T cell transforms into several subsets causing the release of cytokines as well as direct attack of infected cell The endpoint is the production of cytokines o Cytokines - IL, CSM o Cytokines are released after antigen recognition Cell-mediated immune response o CD4 cells respond to antigen recognition (Class II) o CD8 cells respond to antigen recognition (Class I) o Mitogen stimulation of T and B lymphocytes T Cells and Cell Mediated Immunity o Antigens that stimulate this response are mainly intracellular. o Requires constant presence of antigen to remain effective. o Unlike humoral immunity, cell mediated immunity is not transferred to the fetus. o After presentation to antigen and activation, antigensensitive T cell with the antigen activates B cell which transforms into plasma cell/plasmacyte o Only when B cell are transformed into plasma cell they can produce immune response in the form of antibody/immunoglobulin production/release • Primary Humoral Immune Response o Initial exposure but there is none to minimal ab prod. o Log Phase - About 1 to 2 weeks for a measurable amount of antibody to be observed o Exponential Phase - Rapid increase in the concentration of antibodies observed o Steady State/Plateau - Production and degradation of antibodies are balanced o Decline Phase - Immune system begins to shut down • Secondary Humoral Immune Response o Also called the Booster or Anamnestic Response o Second exposure to the same antigen will trigger memory T and B lymphocytes o Memory cell - remembers previous exposure & allows immediate immune response during 2nd exposure • Occur in 3 phases: 1. Antigen elimination – accomplished by phagocytosis. Most injected Ag is removed within minutes, but complete removal may take months or years 2. The primary response – after exposure to Ag, there is latent pd of approx. 5 to 15 days before antibody appears in the serum. IgM is the first Ig to appear. (majority of Ig produced during primary response); ab titer increase, plateaus, then dcreases. 3. The secondary response – second or subsequent exposure to the same antigen elicits secondary response. there is rapid antibody response usually within 2 to 4 days after antigen exposure. IgG is the predominant. Circulating ab titer is much higher and lasts longer than that seen in primary. Primary Response Secondary Response Duration Long lag phase, Short lag phase, long short plateau, and plateau, and gradual rapid decline decline Cells Plasma cells Memory cells Type of ab IgM IgG Antibody titer low high Antibody affinity Low high Antibody avidity High (↑ valence) high • IgM - primitive immunoglobulin CYTOKINE STORM HUMORAL IMMUNE RESPONSE • • Humoral Immunity – involves B cell activation, production of antibodies in blood plasma and lymph. o Action of B cells o B cells are stimulated by T cells to become plasma cells to release/induce production of antibodies Process of Humoral Response o Antigen enter the body and macrophages engulfs and process antigens o Antigen presented by macrophages will not be recognized by T cell unless there is presence of HLA Class I/II ▪ CD8+ T cell - requires HLA Class I ▪ CD4+ T cell - requires HLA Class II • • • • Monokine - produces monocytes Lymphokines - produced by lymphocytes Cytokine storm and cytokine release syndrome are lifethreatening systemic inflammatory syndromes involving elevated levels of circulating cytokines and immune-cell hyperactivation that can be triggered by various therapies, pathogens, cancers, autoimmune conditions, and monogenic disorders. The laboratory findings in cytokine storm are variable and influenced by the underlying cause. Nonspecific markers of inflammation such as C-reactive protein (CRP) are universally elevated and correlate with severity. Many patients have hypertriglyceridemia and various blood-count abnormalities, such as leukocytosis, leukopenia, anemia, thrombocytopenia, and elevated ferritin and d-dimer levels. ASSAYS OF IMMUNE COMPETENCE ENUMERATION AND FUNCTIONAL ASSAYS OF T CELLS T-CELL DIFFERENTIATION • • • • • • Clinical Presentation of Cytokine Storm • • • • T cells are key cellular component of immunity Early surface markers - CD44 and CD25. Two main subsets of T cells to mature: o CD4+ ▪ Helper T cells that indirectly protect from fungi and bacteria by secretion of cytokines to activate B cells to maturity and produce antibody. o CD8+ ▪ Cytotoxic T cells that directly protect from viral infection by cell lysis Double-Negative Stage o Early thymocytes lack CD4 and CD8 markers Double-Positive Stage o express both CD4 and CD8 antigens o Cells that fail positive selection are eliminated within the thymus by apoptosis Mature T Cells o Two major events occur: ▪ The development of two distinct T-cell populations CD4+ (helper-inducer); CD8+ (suppressor-cytotoxic) ▪ The loss of Tdt enzyme T helper cells consist of two subsets. o Th1 cells ▪ produce interferon gamma and tumor necrosis factor-beta ▪ protect cells against intracellular pathogens ▪ responsible for cell-mediated effector mechanism o Th2 cells ▪ produce a variety of interleukins, IL-4, IL-5,IL-10, and IL-13 ▪ essential role is to help B cells produce antibody against extracellular pathogens T Helper (TH) Cells o Central role in immune response o Most are CD4+; CD8o Recognize antigen on the surface of antigen presenting cells (e.g.: macrophage). o Activate macrophages o Stimulate B cell growth and differentiation o 50-60% in the peripheral blood o produces IL-2, IL-3, GM-CSF, IFN-gamma • • Cytotoxic T (Tc) Cells o Destroy target cells o Most are CD4 negative (CD4 -),CD8+ o Recognize antigens on the surface of all cells o Kill host cells that are infected with viruses or bacteria o Recognize and kill cancer cells. o Recognize and destroy transplanted tissue. o Release protein called perforin which forms a pore in target cell • • T Suppressor (Ts) Cells o May shut down immune response o downregulate the actions of T & B cells o no unique markers. ENUMERATION AND FUNCTIONAL ASSAYS OF B CELLS PHAGOCYTOSIS B-CELL DIFFERENTIATION • • Antigen Independent Phase o Pro-B Cells ▪ Earliest B-cell precursor – recognized by surface molecule CD45R ▪ distinctive markers CD19, CD45R, CD43, CD24, and c-Kit. o Pre-B Cells ▪ Ig gene rearrangement ▪ CD10 and CD19 o Immature B Cells ▪ distinguished by the appearance of complete IgM molecules on the cell surface ▪ CD21, CD 40, and major histocompatibility complex (MHC) class II molecules.expresses IgM on surface o Mature B Cells ▪ IgM and IgD on cell surface. ▪ have a half-life of more than 6 weeks. Antigen Dependent Phase o Activated B Cells ▪ CD25, receptor (IL-2). ▪ live for years as memory cells ▪ quickly transform to plasma cells and begin producing IgG ▪ secondary antibody response. o Plasma Cells ▪ end stage of B-cell differentiation ▪ No further maturation ▪ CD19 ▪ not normally found in the circulating blood ▪ relatively short-lived • • LABORATORY IDENTIFICATION OF LYMPHOCYTES • Most methods are based on separation of mononuclear cells from whole blood and detection of specific cell surface markers. Method for Obtaining Lymphocytes o Density gradient centrifugation with FicollHypaque ▪ Layers from top to bottom: plasma, mononuclear cells, Ficoll-Hypaque, RBCs, granulocytes Methods for Identifying Lymphocytes o Cell flow cytometry (FACS – FluorescenceActivated Cell Sorter) ▪ Use of labeled monoclonal antibodies against specific surface antigens. ▪ Light scattering is measured as cells flow through a laser beam. ▪ Automated o Rosette Technique ▪ Old method; manual ▪ T lymphocytes (CD2) form rosettes with sheep’s RBC o Direct or Indirect Immunofluorescence ▪ Use of labeled monoclonal antibodies against specific surface antigens. Slides are read with a fluorescent microscope. o Surface immunoglobulins ▪ Immunoenzymatic method to demonstrate immunoglobulins on B cells • Process of Phagocytosis 1. Initiation 2. Phagocytosis is initiated as a result of tissue damage 3. Activated phagocytosis increased surface receptors that allows adherence to the bacterium 4. Chemotaxis ▪ process in which cells tend to move in certain direction under stimulation of chemical substances ▪ Example of chemotaxins – C5a, C5b, C6, C7 5. Recognition and adherence ▪ Opsonization ▪ Cell surface receptors: Fc receptor, complement receptor 6. Engulfment 7. Fusion and degranulation 8. Killing and Digestion ICED o Initiation → Chemotaxis → Engulfment → Digestion