title: Immunological mechanisms of human platelet involvement.
abstract: Several immunological mechanisms of platelet involvement in inflammation are described. Basophils degranulate and release a platelet-activating factor (PAF) when challenged with anaphylotoxins, cationic proteins (CP) from polymorphonuclear cells (PMN) as well as with specific antigens from atopic patients. PAF is a newly-discovered mediator of anaphylaxis present in rabbit and human basophils. This factor is a small phospholipid, probably a lyso-1-phosphatidylcholine with a significant aggregating activity on rabbit and human platelets. PAF is released, together with a small amount of arachidonic acid, from basophils in the presence of anaphylotoxins, CP and specific antigens from atopic patients. The already well-known direct interaction between immune complexes (Ics) and human platelets is compared here with the mechanism of PAF-induced aggregation. It is shown that the latter process of aggregation differs from the former. Human platelet aggregation starts more rapidly in the presence of PAF than of Ics. PAF-induced aggregation is ADP-independent as it is not affected by ADP inhibitors. On the contrary, Ic-dependent aggregation is brought about by endogenous ADP release and therefore inhibited by ADP inhibitors. The interaction between Ics and platelets leads to the release of CP. The latter produce a cascade reaction involving basophils which degranulate and release PAF. A self-maintaining mechanism of tissue injury is thus triggered.
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000706:Anaphylatoxins / Q000494:pharmacology; D000936:Antigen-Antibody Complex; D001095:Arachidonic Acids / Q000378:metabolism; D001491:Basophils / Q000187:drug effects*; D001779:Blood Coagulation Factors / Q000502:physiology*; D001792:Blood Platelets / Q000276:immunology*; D001798:Blood Proteins; D008244:Lysophosphatidylcholines / Q000378:metabolism; D010974:Platelet Aggregation
chemical_list: D000706:Anaphylatoxins; D000936:Antigen-Antibody Complex; D001095:Arachidonic Acids; D001779:Blood Coagulation Factors; D001798:Blood Proteins; D008244:Lysophosphatidylcholines; D000244:Adenosine Diphosphate