The immune system is divided into cellular and
humoral immunity. The humoral immunity involves natural barriers that protect
against invasion by microorganisms. Cellular immunity involves cells such as
mast cells, macrophages, lymphocytes, granulocytes etc. To defend the body, the
antigens are recognized and presented to the immune cells by antigen presenting
cells. The T-helper cells help in recognizing pathogens. If the pathogen is a bacterium,
it triggers neutrophil production. If its virus, it triggers the lymphocytic
response. Parasites trigger release of esinophils. Mast cells produce histamine
in response to allergic stimuli such as pollen. After the antigen is presented
to immune cells, the body may trigger an inflammatory response that supposed to
help in getting rid of the pathogen. However, at times this may get out of hand
and be detrimental to the persons health, e.g. in Asthmatic attack.
T-suppressor cells reduce the level of the body response to pathogens and may
serve to reduce inflammation. Natural killer cells are part of T-lymphocytes
and they kill any cell that cannot be recognized by the body as ‘being own’.
They are part of cellular immunity. Antibodies are produced by type B
lymphocytes and they neutralize antigens that are circulating in the body to
cause illness. Macrophages are found in various tissues such as lungs, liver
and spleen where they capture and engulf invading microorganisms such as
bacteria and kill/digest them
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