See also acne . 1. living on or within another organism, and deriving benefit without injuring or benefiting the other individual. 2. denoting a donor and recipient of a blood transfusion in which there is no transfusion reaction. In psychology, a conscious process or, more frequently, an unconscious defense mechanism by which a person attempts to make up for real or imagined physical or psychological deficiencies. In cardiology, the maintenance of an adequate blood flow without distressing symptoms, accomplished by such cardiac and circulatory adjustments as tachycardia, cardiac hypertrophy, and increase of blood volume by sodium and water retention.
Complement activation occurs by two different sequences, the classic and alternative pathways.
The proteins of the classic pathway are termed 'components of complement' and are designated by the symbols C1 through C9. Fragments resulting from proteolytic cleavage of complement proteins are designated with lower-case letter suffixes, e.g., C3a. Inactivated fragments may be designated with the suffix 'i', e.g. C3bi. The alternative pathway can be activated by IgA immune complexes and also by nonimmunologic materials including bacterial endotoxins, microbial polysaccharides, and cell walls. Both result in the cleavage of C5 and the formation of the membrane attack complex.