Complement pathways and meningococcal disease : diagnostic aspects.

Complement is an immunological effector system that bridges innate and acquired immunity in several ways. There is a striking association between susceptibility to meningococcal disease and various forms of complement deficiency (1,2). In defense against bacterial infection, the most important function of complement is probably to serve as a mediator of antibody-dependent immunity. Specific antibodies can trigger activation of the classical and the alternative pathways of complement activation (3-5). It is well known that antibody-independent mechanisms interfere with alternative pathway activation on the bacterial surface (6,7). The newly discovered mannan-binding lectin (MBL) pathway of complement activation appears to be protective against many types of infection (8) and adds previously unsuspected aspects of innate immunity to complement-mediated defense. Interestingly, immune responses are influenced by complement (9), and it could be that acquisition of protective antibodies is impaired in some types of complement deficiency. A further aspect of interactions between Neisseria and complement is the potential role of membrane-bound complement regulators as cellular receptors for the microbes (7).