Retardation of cell cycle progression of macrophages from G1 to S phase by ICAM-L from Leishmania.

Leishmania, an obligate intracellular parasite of host macrophages, infects the macrophage through receptor-mediated phagocytosis that either activates or deactivates macrophages to eliminate the parasite or allow the parasite to grow intracellularly. ICAM-L, an intercellular adhesion molecule from L. amazonensis, results in lower MTT tests and proliferative responses of macrophages when incubated in vitro. The inhibition of cell proliferation, however, results from temporary retardation of the cell cycle progression at the G1 to S phase transition rather than cell death. The retardation is due to the upregulation of two CKI proteins, p21 and p27, in a p53-independent manner which, control the G(1) to S phase transition checkpoint.