神奇的免疫系统 THE MAGICAL IMMUNE SYSTEM
What is a T4 lymphocyte?
It is a type of white blood cell.
T4 lymphocytes, also known as "Helper cells", are a type of white blood cell that orchestrate the immune response and enhance the activities of the killer T-cells (those that destroy pathogens) and B-cells (antibody and immunoglobulin producers).
White blood cells are released by the immune system when the body is under threat (often from bacteria or a virus). The T4 lymphocytes help the response to a threat by triggering the maturation of other types of white blood cell. They produce special proteins, called cytokines, which act like a 999/911 call and summon all of the other immune cells to the area, or it causes nearby cells to differentiate (become specialised) into mature T-cells.
It is worth noting that in AIDS, the number of T4 cells decreases drastically.
Oxygen-dependent myeloperoxidase-independent intracellular killing (Figure11A)
During phagocytosis glucose is metabolized via the pentose monophosphate shunt and NADPH is formed. Cytochrome B which was part of the specific granule combines with the plasma membrane NADPH oxidase and activates it. The activated NADPH oxidase uses oxygen to oxidize the NADPH. The result is the production of superoxide anion. Some of the superoxide anion is converted to H2O2 and singlet oxygen by superoxide dismutase. In addition, superoxide anion can react with H2O2 resulting in the formation of hydroxyl radical and more singlet oxygen. The result of all of these reactions is the production of the toxic oxygen compounds superoxide anion (O2-), H2O2, singlet oxygen (1O2) and hydroxyl radical (OH•).
Oxygen-dependent myeloperoxidase-dependent intracellular killing (Figure 11B)
As the azurophilic granules fuse with the phagosome, myeloperoxidase is released into the phagolysosome. Myeloperoxidase utilizes H2O2 and halide ions (usually Cl-) to produce hypochlorite, a highly toxic substance. Some of the hypochlorite can spontaneously break down to yield singlet oxygen. The result of these reactions is the production of toxic hypochlorite (OCl-) and singlet oxygen (1O2).
NATURAL KILLER CELLS
Natural killer cells (also known as NK cells, K cells, and killer cells) are a type of lymphocyte (a white blood cell) and a component of innate immune system.
NK cells play a major role in the host-rejection of both tumours and virally infected cells.
NK cells are cytotoxic; small granules in their cytoplasm contain special proteins such as perforin and proteases known as granzymes.
Upon release in close proximity to a cell slated for killing, perforin forms pores in the cell membrane of the target cell through which the granzymes and associated molecules can enter, inducing apoptosis.
The distinction between apoptosis and cell lysis is important in immunology - lysing a virus-infected cell would only release the virions, whereas apoptosis leads to destruction of the virus inside.
NK cells are activated in response to interferons or macrophage-derived cytokines.
They serve to contain viral infections while the adaptive immune response is generating antigen-specific cytotoxic T cells that can clear the infection.
Patients deficient in NK cells prove to be highly susceptible to early phases of herpes virus infection.
Natural killer cell