The Role of Complement in Host Resistance to Bacteria
Some of the earliest observations that led to our current understanding of the function of the complement system were made just before the turn of the century when it was noted that fresh blood had the power to kill certain types of bacteria [3, 17]. Analysis of the bactericidal activity of blood led to the recognition of factors called into play by the presence of specific antibodies to the bacterial surface that were responsible for the lytic of bactericidal event. Because early investigators thought that this activity occurred only after the binding of antibody, it was called complement. More detailed analysis of these factors elucidated the protein components active in the “classic” complement pathway, or cascade, and later that in the “alternative” pathway. As our understanding of this system developed, it became clear that complement plays a major role in protecting the individual from overwhelming bacterial infection and participates in both “specific” and “nonspecific” immunity. Complement mediates its effects through at least two important mechanisms. The first to be recognized was the bactericidal reaction, that is, the direct complement killing of microorganisms; later, it became clear that complement proteine act as opsonins, coating bacteria with protein fragments which are recognized with great specificity by phagocytic cells and which facilitate the phagocytic process.
KeywordsNeisseria Gonorrhoeae Bacterial Surface Membrane Attack Complex Alternative Complement Pathway Serum Killing
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