Activation of the alternative pathway of complement by mycobacteria and cord factor.

The ability of a number of mycobacteria and some of their components to activate complement was examined. Mycobacterium bovis BCG (Glaxo strain), Mycobacterium leprae, Mycobacterium lepraemurium, and cord factor activated the alternative pathway of complement in normal human serum and normal and C4-deficient guinea pig sera and generated biologically active products. BCG (Pasteur strain) and muramyl dipeptide did not activate complement. The relevance of activation of complement by mycobacteria to their induction of granulomas is discussed.