Abstract:

Objective To explore the role of innate immunity in the pathogenesis of leptospirosis by comparing the viability of Leptospira in mononuclear macrophages of human and mouse origin. Methods Human monocytic cell lines (THP-1) treated with phorbol myfismte acetate (PMA) to be differentiated into macrophages and murine mononuclear macrophages cell lines (RAW264.7) were infected with Leptospira interrogans serovar Autumnalis strain autumnalis #56606 (56606v) and avirulent strain (56606a) in vitro. Laser scanning confocal microscopy was employed to determine the percentages of cells with intracellular leptospires in these two cell lines with immunofluorescence staining 2 h, 24 h and 72 h after infection, and Real-Time PCR was used to detect the expression of 16S rRNA of leptospires in these two cell lines 2 h, 12 h, 24 h, 48 h and 72 h after infection, which indirectly reflected the viability of intracellular Leptospira. Results The percentages of THP-1 and RAW264.7 cells with leptospires decreased with time of infection. RealTime PCR revealed that the expression of 16S rRNA of leptospires in these two cell lines decreased with time of infection, and the numbers of intracellular viable leptospires also decreased with time of infection. Conclusion Leptospira can not survive and replicate within macrophages of human or mouse origin, which indicates that anti-degradation of macrophages by pathogenic Leptospira may not be the major pathogenic mechanism of leptospirosis. Further studies are required to interpret the pathogenesis.

Key words: Leptospira, macrophages, viability, Real-Time PCR