Antibodies as Tools – Diagnostics and Therapy PDF

Using antibodies as tools – diagnostics, therapy Highly specific binding of antibodies makes them useful for - detecting the presence of pathogen, host cells or molecules - therapy to inactivate toxins, inflammatory cytokines, cancer cells  ELISA: Enzyme-linked Immunosorbant Assay Using...

Using antibodies as tools – diagnostics, therapy Highly specific binding of antibodies makes them useful for - detecting the presence of pathogen, host cells or molecules - therapy to inactivate toxins, inflammatory cytokines, cancer cells  ELISA: Enzyme-linked Immunosorbant Assay Using antibodies to detect pathogens and pathogen infections 1. Antigen-capture Antibody specific for pathogen antigen is used to coat wells Antigen in patient samples will be bound if present A second, enzyme-conjugated antigen-specific antibody will bind the captured antigen. Enzyme activity produces colored product 2. Antibody-capture Pathogen antigen is used to coat well of 96-well plastic plate Antibodies in patient serum samples can bind the antigen Presence of bound antibodies is detected using an anti-human antibody with conjugated enzyme. Enzyme activity produces colored product Rapid diagnostic tests can be performed in the clinic The gold-labeled antibody that is bound to antigen is detected only when antigen is retained in a narrow strip by a second antibody bound to the filter (solid-phase). Excess, unbound antibody, continues to diffuse until it is bound by anti- antibody in a narrow strip farther up the filter - this control shows that the antibody is present and has diffused past the point where it would be retained if antigen were in the sample.  T cell effector functions killer cells helper cells Cytotoxic and Helper T cell lineages develop in the thymus and are marked by CD8 and CD4 surface molecules respectively  T cells provide immune function using a strategy similar to B cells. A huge number of unique specificity T cell clones are generated during development. Recognition of antigen by mature T cells leads to clonal activation and differentiation into either effector or memory cells. Activated effector T cell memory cells precursor naive population activated clone within population Effector/Memory cells Individual T cells express a unique specificity antigen receptor which is generated during development in the thymus by gene segment rearrangement. Lymphoid precursor cells enter the thymus to become T cells The thymus can express most self antigens and present them on antigen- presenting cells (APCs)  T cells are activated in secondary lymphoid tissue. Pathogens arrive at regional nodes by traveling through the lymph, or after ingestion by dendritic cells which will migrate when activated.  T cells recognize pathogens only indirectly. The only pathogen structures that T cells recognize are short pathogen peptides that are presented to them on the surface of infected cells, or specific immune cells - Dendritic cells, Macrophages, B cells. Cells use the Major Histocompatibility Complex (MHC) proteins to present pathogen peptides to T cells.  Pathogen peptides are generated following intracellular proteolysis and transported to the cell surface bound to either class I or class II MHC molecules. MHC I pathway presents antigens from the cytosolic compartment while the MHC II pathway presents antigens from the extracellular/vesicle compartment.  T cell activation requires T cell receptor (TCR) aggregation with pepetide-MHC complexes, aided by co-receptor CD4, or CD8, binding to MHC molecules. MHC I is bound by the TCR and CD8 on cytotoxic T cells, MHC II is bound by the TCR and CD4 on helper T cells. Once activated, CD8+ cytotoxic T cells can kill pathogen infected cells through the release of cytotoxic enzymes that induce apoptotic pathways - similar to the mechanisms used by NK cells. A variety of CD4 Thelper cell subsets can be produced by activation. CD4+ T cell subsets are distinguished by the cytokines they produce and the cells that they target. T helper -1 cells secrete interferon- gamma to stimulate phagocytic cells IFN-gamma and improve killing of internalized pathogens. TH-1 cells also help activate Cytotoxic T cells through secretion of Interleukin-2 cytokine. IL-2 T helper-2 cells provide IL-4 and other cytokines to promote proliferation and differentiation of B cells. The type of effector T cell response is matched to the type of pathogen infection in order to provide the most useful immune response.