뒤로Microbiology: Immunity and Antigen Presentation
05:52
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Innate immunity is the immediate, non-specific defense present at birth. Adaptive immunity is specific, develops memory, and improves upon repeated exposure to pathogens.
Specificity is the immune system's ability to target specific antigens. Memory allows faster response upon re-exposure. Tolerance prevents immune response against self-antigens.
MHCI is expressed on all nucleated cells and presents intracellular antigens. MHCII is expressed mainly on antigen-presenting cells and presents extracellular antigens.
Intracellular antigens are degraded by proteasomes, loaded onto MHCI molecules in the ER, and presented on the cell surface for recognition by CD8+ T cells.
Extracellular antigens are endocytosed, degraded in endosomes, loaded onto MHCII molecules, and presented on APC surfaces for CD4+ T cell recognition.
APCs process and present antigens to T helper cells, activating B cells to produce antibodies. The three main APCs are dendritic cells, macrophages, and B cells.
TCR has two peptide chains and one epitope binding site; it recognizes antigen peptides presented by MHC. BCR has two heavy and two light chains with two binding sites and recognizes free antigens.
Antibodies neutralize toxins/pathogens, opsonize for phagocytosis, and activate the complement system to lyse pathogens.
T helper cells express CD4, activate other immune cells, and recognize MHCII. T cytotoxic cells express CD8, kill infected cells, and recognize MHCI.
APCs present antigen on MHCII to T helper cells, which then activate B cells to produce antibodies targeting extracellular pathogens.
Cell-mediated immunity involves T cells targeting infected cells. Humoral immunity involves B cells producing antibodies against extracellular pathogens.
IgA is found in mucosal areas, protects mucous membranes, and exists mainly as a dimer.
IgM is the first antibody produced in an immune response, exists as a pentamer, and is effective at complement activation.
IgG is the most abundant antibody in serum, provides long-term immunity, and can cross the placenta.
IgE is involved in allergic responses and defense against parasitic infections by binding to mast cells and basophils.
Isotype switching is the process by which B cells change the antibody class they produce without altering antigen specificity, affecting immune response and serological testing.