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Metabolic component: The third line of defense is slow, best measured by the base excess, [9] and mostly depends on the renal system which can add or remove bicarbonate ions (HCO − 3) to or from the ECF. [5] Bicarbonate ions are derived from metabolic carbon dioxide which is enzymatically converted to carbonic acid in the renal tubular cells.
In the first line of defense, inhaled bacteria are trapped by mucus and are swept toward the pharynx and are swallowed. [1] Bacteria which penetrate the mucous layer are dealt with a second line of defense which includes antimicrobial peptides that are secreted by the surface epithelium of the respiratory tract which kill many strains of ...
The cells of the adaptive immune system are special types of leukocytes, called lymphocytes. B cells and T cells are the major types of lymphocytes and are derived from hematopoietic stem cells in the bone marrow. [57] B cells are involved in the humoral immune response, whereas T cells are involved in cell-mediated immune response.
When host cells die, either by apoptosis or by cell injury due to an infection, phagocytic cells are responsible for their removal from the affected site. [9] By helping to remove dead cells preceding growth and development of new healthy cells, phagocytosis is an important part of the healing process following tissue injury.
The activation of T H 1 and M1 macrophage is a positive feedback loop, with IFN-γ from T H 1 cells upregulating CD40 expression on macrophages; the interaction between CD40 on the macrophages and CD40L on T cells activate macrophages to secrete IL-12; and IL-12 promotes more IFN-γ secretion from T H 1 cells.
Dendritic cells are tree-like cells that bind antigens and alert the lymphocytes of infection, essentially directing T cells to make an immune response. Complement proteins are proteins that play a role in the non-specific immune responses alongside these non-specific immune cells to make up the first line of immune defense. [4]
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Scheme of the complement system. The complement system, also known as complement cascade, is a part of the humoral, innate immune system and enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. [1]