Phagocytosis of virulent and avirulent leptospires by guinea-pig and human polymorphonuclear leukocytes in vitro.

Chemiluminescence (CL) and electron microscopy were used to study the phagocytosis of both virulent and avirulent strains of Leptospira interrogans serovar copenhageni by guinea-pig and human polymorphonuclear leukocytes (PMN). A significant CL response was observed when guinea-pig PMN were incubated with virulent leptospires in the presence but not in the absence of specific immune serum. This response was markedly enhanced by the addition of guinea-pig complement. Phagocytosis was confirmed by the observation of intracellular leptospires in guinea-pig PMN by electron microscopy. The phagocytosis of avirulent leptospires by guinea-pig PMN and of both virulent and avirulent leptospires by human PMN required the presence of both specific immune serum and complement. Thus the ability of leptospires to resist phagocytosis by PMN in the absence of immune serum does not appear to be a major determinant of virulence.