Complement-mediated Killing of Leishmania martiniquensis Promastigotes

Background: Leishmaniasis caused by various species is now an emerging autochthonous disease. L. martiniquensis was described first from a human case in Martinique island and to date is frequently causing human infections in many countries. To eliminate the invading pathogen, complement activation of the innate system plays an effective role in the host’s defense. This study aims to test the parasiticidal activity of the complement activation against L. martiniquensis promastigotes.

Methods: An in vitro examination of parasite mortality rate incubated in fresh normal human serum (NHS) was performed compared to heat-inactivated, and ion chelated sera.

Results: We observed a lethal effect on the parasite when exposed to fresh NHS. Our parasites when tested with heat-inactivated at 56 0C for 30 min and ethylene diamine tetra acetic acid (EDTA) chelated sera indicated complement dependent parasiticidal activity. Ethyleneglycol tetraacetic acid (EGTA) chelated, and EDTA+MgCl2 treated sera demonstrated that L. martiniquensis promastigotes activated the complement via alternative pathway. This pathway was also revealed when the parasite was subjected to zymosan treated sera and that of the heat inactivated (500C for 15 min). Interestingly, positive mannose-binding lectin (MBL) of the parasite surfaces demonstrated by using anti- MBL antibody immunofluorescent test.

Conclusion: The parasitical activity is antibody independent mediated via the alternative pathway. The involvement of MBL could not exclude. These preliminary data might provide a further study for the explanation of the immune evasion strategy of the Leishmania species.