Immunology LU2 : Part 3

Immunology LU2 : Part 3

1. Acquired Immunity

   • Humoral mediated
     • 2 phases
       • Activation : phagocytosis of foreigns by macrophages, digest antigens, components display on surfaces, Helper T cell recognize, activate immune response- multiply rapidly
       • Effector : Begins with B cell, antibodies binds to antigen, cell engulfs the complex via endocytosis, enzyme digests into fragments, attached to class II MHC molecules, displayed on B cells surface, T helper cell from clone cells in activation phase binds, TH cells release cytokines stimulate B cell to divides.
     • Antibodies (Immunoglobulins)
       • Light chain
         • one variable (VL) one constant domain (CL)
       • Heavy chain (5 classes)
         • IgA
           • main Ig in secretion of milk,salive, tears and secretions - respiratory, intestinal, genital tracts , attacks pathogens before access to internal tissues
         • IgD
           • may acts as an antigen receptor when present on B lymphocytes surface in fetal cord blood, occurs on some lymphatic leukimia, sensitization
         • IgG
           • defense against bacteria and viruses, can pass through placenta, resistance against many pathogens
         • IgM
           • main Ig produces in first responses. Eg. Anti-A & Anti-B on blood surface responsible for agglutination
         • IgE
           • analphylactic hypersensitivity, parasitic infections
   • Cell mediated
     • depends on direct interactions between T cells and host body cells bearing antigen (recognize by T cells)
     • Major Histocompatibility Complex (MHC)
       • 2 pathways
         • class MHC I : found on all nucleated cells - CD8 Tc cells recognize antigen
           • binds with peptides from pathogens which replicate in cytosol), killing the cells containing them, CD8 co-receptors helps cytotoxic T cells recognize peptide: MHC I complexes on surface of infected cells
         • class MHC II : expressed by B lymphocyes, interdigitating dendritic cells, thymic epithelial cells - CD4 Th cells recognize antigen
           • binds with antigen derived from protein degraded in intracellular vesicles come form bacteria , intracellular parasites that replicate in macrophages vesicles & toxin ingested extracellularly , APC engulf antigen via endocytosis, endosome fuses with lysosome (antigen degraded into fragments which displayed at cell nestled with class MHC II molecules surface)
         • Antigen processing & presentation
           • APC degrades antigen into small peptides, link peptides to MHC molecules, express on its cell surface, depends on how antigen entered the cells
       • requires in recognization of antigen, can be found on surface of APCs , antigens fragments pair up with MHC molecules, then interact with T cells
   • Stages
     • 1. Recognization
       • recognize presence of pathogens , detect and response
     • 2. Discrimination
       • discriminate between microorganism and normal body cells
     • 3. Implementation
       • actions eliminate the microbial threat