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Introduction to the immune system
MHC class I and MHC class II molecules
B-cell activation and differentiation
Cell-mediated immunity of CD4 cells
Cell-mediated immunity of natural killer and CD8 cells
Somatic hypermutation and affinity maturation
Contracting the immune response and peripheral tolerance
B- and T-cell memory
Anergy, exhaustion, and clonal deletion
Type I hypersensitivity
Type II hypersensitivity
Type III hypersensitivity
Type IV hypersensitivity
Innate immune system
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Your immune system is like the military - with two main branches, the innate immune response and the adaptive immune response.
Key features of the innate immune response are that the cells are non-specific, meaning that they don’t distinguish one invader from another invader, the response is really fast - occurring within minutes to hours, and there’s no memory associated with innate responses.
The adaptive response, which is mediated by lymphocytes like B and T cells - is the opposite of the innate immune response.
B and T cells have unique receptors - the B cell receptor and T cell receptor - that differentiate pathogens from each other using their unique parts - called antigens.
These receptors are developed while the T cell or B cell is developing in the bone marrow for B cells or thymus for T cells.
Once the cell has a unique antigen-specific receptor expressed on its surface it begins traveling through the lymphatic system - passing through lymph nodes in search for the one antigen that fits the receptor perfectly.
If they encounter that antigen, a signal gets delivered to the cell’s nucleus that lead to clonal expansion.
That’s where a single T cell or B cell replicates over and over - creating an army of clones that can combat the pathogen.
Once the immune response is complete, many of these cells die by apoptosis restoring the immune response to its original size - with one major change.
Some of the B and T cells become memory cells, which are basically a pool of lymphocytes that are all set to combat the pathogen, if they encounter it again!
B and T cells are the two main types of lymphocytes or white blood cells that play a role in the immune response. Both B and T cells can remember previous encounters with foreign antigens, which helps them to quickly and effectively respond to future infections by the same microorganisms.
B cells produce antibodies, which bind to pathogens and mark them for destruction by other immune cells. T cells kill infected host cells or help B cells produce more antibodies. Memory B and T cells persist in the body for many years, providing lifelong protection against reinfection by the same pathogen.
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