Abstract:
The superoxide anion (O·
2
-) is the first free radical produced in phagocytes which enables
pathogen killing and also generates other microbicidal reactive oxygen species (ROS).The
induction of high O·
2
- production by phagocytes as a virulence factor for pathogenic
Leptospira is not known. The objective of this study was to assess the induced O·
2
-
production by human neutrophils exposed Leptospira and compare the differences in the
level of O·
2
- produced by HL-60 derived neutrophils interacted with pathogenic and
saprophytic Leptospira spp. HL-60 cells were treated with dimethyl sulfoxide to differentiate
in to mature neutrophils. Saprophytic Leptospira biflexa serovar Patoc and pathogenic L.
Interrogans serovar Pyrogenes were grown in Ellinghausen-McCullough-Johnson-Harris
media containing 10% heat inactivated rabbit sera. Intracellular O·
2
- production of
neutrophils interacted with bacteria in the presence of sera from leptospirosis patients
(n=30/group of severe and mild leptospirosis patients) and healthy subjects (n=20) was
assessed using quantitative nitroblue tetrazolium assay. Both anti-leptospiral IgM and IgG
levels were measured in test sera prior to the assay. In the presence of normal and also
patients’ sera, neutrophils interacted with L. Interrogans Pyrogenes produced significantly
high O·
2
- levels than that of L. biflexa (p<0.05). When Leptospira density was varied for
neutrophil-bacteria interactions, low Leptospira densities induced higher O·
2
- productions
compared to the high concentrations (p<0.03). Moreover, analysis of O·
2
- production by
neutrophils in the presence of patients’ sera showed that, opsonization of both saprophytic
and pathogenic Leptospira by IgM or IgG had not induced a significant difference in the
level of O·
2
- produced (p = 0.012). These results suggest that, the increased O·
2
- production
induced by L. Interrogans Pyrogenes could be a virulent factor in pathogenic Leptospira
spp which may contribute to the pathogenesis of severe leptospirosis.
