Tuberculosis Research Centre, Chetpet, Chennai.
The complement system is not only a part of the innate immune system but it also occupies a bridging position between the afferent and efferent limbs of the adaptive immune system. More recently, its role in modulating both the humoral and the cellular limbs of the immune system is also being recognized. Thus, from an earlier concept of this system being complementary to the host response against foreign antigens, we are moving towards a more pivotal role that these components could play in helping the host to adapt itself more optimally to the environment.
The major pathogenic mycobacteria, namely, Mycobacterium tuberculosis and M.leprae have been shown to be potent activators of the complement system. Many of the components of these mycobacteria also are potent activators of this system. These include both the secreted and the integral components of the bacterium.
The interaction of mycobacteria with the complement system has consequences to both the host and the bacterium. A large body of evidence available now indicates that this interaction confers greater advantage to the bacterium than the host. The host appears to suffer in two ways. Mycobacteria use the complement system to evade the protective response. Antibodies against the bacterium appear to aid this process greatly. Secondly, this interaction results in the release of phlogistic components which damage the host tissue.
All the same, a better understanding of this interaction can not only help us to devise therapeutic strategies to minimize the immune damage but also to develop a vaccine with a newer and more capable way of combating mycobacterial infections.
