Discussion

A model system has been developed to study the effect of Leishmania mexicana parasite virulence status on their interaction with host cells. Parasite freshly isolated from Balb/c mice skin lesions were grown in vitro (passage 1-highly virulent (P1)) and subsequently sub-cultured for 20 passages. Parasites lost their virulence with time and completely failed to infect Balb/c mice at passage 20 (P20). The in vitro growth characteristics of P1 and P20 parasite were similar. In this study, the interaction of P1&P20 with monocytic human cell line (U937) and Balb/c bone marrow macrophages has been assessed using parasite cell count, parasite morphology and the expression profile of IL-6 and IL1 b cytokines. The number of free extracellular P1 parasites was significantly lower than that of P20 whether in host cells of U937 cells or bone marrow macrophages. Significant morphological differences between P1 & P20 in infected cultures were also observed, P1 parasite cells were shorter, more rounded and with short or no flagella. Infection of host cells for 2 or 24 hours with P1 has significantly up-regulated the expression of IL1-b in comparison with the expression of IL-6 as measured by qPCR. In contrast infection with P20 has reversely up-regulated the expression of IL-6 cytokine in comparison with the expression of IL-1. In conclusion this model can be used further to analyse the interaction of Leishmania parasite with host cell.