KINETICS OF ENTRY OF VIRULENT AND AVIRULENT STRAINS OF LEISHMANIA-DONOVANI INTO MACROPHAGES - A POSSIBLE ROLE OF VIRULENCE MOLECULES (GP63 AND LPG)

Specific receptors may be involved in the process of attachment of Lei shmania donovani promastigotes to macrophage surfaces and their subseq uent internalization. Two virulent strains of Indian L. donovani (AG83 and GE-I) were found to enter into macrophages much faster than the a virulent ones (UR6). These virulent promastigotes express surface glyc oprotein (gp63) and lipophosphoglycan (LPG) to a greater extent than a virulent strains. We examined their interaction with macrophages as a function of time by preblocking the macrophage receptors with the exog enous addition of gp33 or LPG. In experiments where gp63 was used as t he blocking agent, the entry of one virulent strain (GE-I) was affecte d. In other experiments where LPG was used, the entry of another virul ent strain (AG83) was affected. Entry of the avirulent strain (UR6) wa s unaffected by either of these treatments. Exposed LPG or gp63 on the surface of promastigotes thus appear to expedite their recognition an d entry into the host cell. To assess the role of gp63 further in the entry of Leishmania into the macrophages, an avirulent UR6 strain was transfected with the gp63 gene cloned from L. amazonensis. The transfe cted UR6 as expected expressed more GP63 at a faster rate and entered into the macrophages like the virulent strain when compared to the non transfected UR6 or UR6 transfected with vector alone. Thus, the expres sion of the gp63 gene is involved in the recognition and intracellular entry of visceral Leishmania into the macrophages in addition to the cutaneous species demonstrated previously.