The role of complement in defence against bacterial disease
Many of the initial observations that led to the discovery of the complement system related to the interaction between serum proteins and bacteria (Rapp and Borsos, 1970; Brown et al, 1984). It was recognized very early that antibody could activate the lytic system present in fresh serum and that certain bacteria could be lysed by this process. Ultimately, it was appreciated that, while Gram-negative bacteria were often lysed by antibody and complement action, Gram-positive bacteria were never lysed. Complement subsequently proved important in its role as an opsonin for Gram-positive bacteria. Further study indicated that the opsonic process was far more important than lysis for protection against infection. In only a few situations does lysis of bacteria per se appear to be of critical protective value (Berger et al, 1981-1982; Fearon and Wong, 1983; Brown et al, 1984; Pangburn and Muller-Eberhard, 1984; Cooper, 1985; Fries and Frank, 1987). It was learned, in addition, that bacteria isolated from clinical materials commonly displayed serum resistance, even if laboratory strains of the same species did not. Thus, resistance to complement attack was often an inherited characteristic associated with increased virulence. Finally, the function of the alternative pathway in host defence against infection was discovered, suggesting how the complement proteins may provide first line defence against bacterial invasion before the formation of specific antibodies (Pangburn and Muller-Eberhard, 1984). These aspects of the complement system are reviewed in this report. Special emphasis is given to our own studies of the role of complement in the host defence process.
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