Induction of novel protein synthesis by opsonized Histoplasma capsulatum ingested by murine peritoneal macrophages.

It is known that Histoplasma capsulatum can resist the intraphagolysosomal environment and multiply inside macrophages. This resistance can be closely related to its pathogenicity. The mechanism of this resistance has been investigated, but it has not been clarified as yet. To learn about the metabolic condition of the yeast-form of H. capsulatum (isolates G217B and CDC 105) when ingested by macrophages, we investigated protein synthesis by ingested H. capsulatum with [35S]-methionine labeling. Cycloheximide at 5 to 10 micrograms/ml was used to preferentially inhibit macrophage uptake of [35S]-methionine without affecting H. capsulatum uptake. Protein synthesis by H. capsulatum in medium alone served as a positive control. The negative control consisted of macrophages with ingested heat-killed H. capsulatum. Analysis of cytosols with SDS-PAGE and fluorography disclosed that, respectively for G217B and CDC 105, ingested H. capsulatum synthesized 4 and 5 novel proteins, increased the synthesis of 9 and 17 proteins and decreased the synthesis of 9 and 10 constitutive proteins. Ten of these novel or increased proteins were apparently common to both strains. These metabolic changes in ingested H. capsulatum could reflect its adaptation to the intraphagolysosomal environment of macrophages and its ability to multiply there.