LEISHMANIA-MAJOR HSP100 IS REQUIRED CHIEFLY IN THE MAMMALIAN STAGE OFTHE PARASITE

In Leishmania major a 100-kDa heat shock protein, Hsp100, is abundant in the intracellular amastigote stage which persists in the mammalian host. A replacement of both clpB alleles which encode Hsp100 does not affect promastigote viability under standard culture conditions but im pairs thermotolerance in vitro. In experimental infections of BALB/c i nbred mice, the lack of Hsp100 in the gene replacement mutants results in a markedly delayed lesion development compared with that in infect ions with wild-type L. major. Overexpression of exogenous clpB gene co pies can partly restore virulence to the gene replacement mutants. Gen etic-selection experiments also reveal a strong pressure for Hsp100 ex pression in the mammalian stage. This requirement for Hsp100 was also observed in in vitro infection experiments with mouse peritoneal macro phages. These experiments indicated a role for Hsp100 during the devel opment from the promastigote to the amastigote stage. Our results sugg est an important role for this parasite heat shock protein during the initial stages of a mammalian infection.