DEVELOPMENTAL-CHANGES IN THE EXPRESSION OF LEISHMANIA-CHAGASI GP63 AND HEAT-SHOCK PROTEINS IN A HUMAN MACROPHAGE CELL-LINE

The ability of the protozoan Leishmania chagasi to infect a vertebrate host depends on its ability to survive intracellularly in a mammalian macrophage. Novel patterns of gene expression are probably important for conversion from the extracellular promastigote to the obligate int racellular amastigote parasite form. We found that the human macrophag e-like cell line U937 provided an in vitro model of phagocytosis of L. chagasi promastigotes and intracellular conversion to amastigotes, al lowing examination of parasite protein and RNA expression. The Leishma nia surface protease gp63 assumed three isoforms during stage conversi on, and a 64-kDa form of gp63 not present in promastigotes became the most prominent form in amastigotes. gp63 RNAs derived from the three d ifferent classes of msp genes (mspS, mspL, and mspC) were also differe ntially expressed. Infectious promastigotes contained mRNAs from mspS and mspC genes, whereas converting parasites expressed only mspL and m spC mRNAs. Sequence analysis of clones from an amastigote cDNA library confirmed the presence of gp63 mRNAs only from mspL and mspC class ge nes in tissue-derived amastigotes. Finally, 24 h after phagocytosis, t here was a transient increase in the level of hsp70 and hsp90 proteins that subsequently decreased to baseline; this increase was not due to heat shock alone. We conclude that a unique pattern of selected L. ch agasi proteins and RNAs is induced following phagocytosis by macrophag es.