Stimulation of endogenous proteolysis in macrophages exposed to sporulating bacteria.

The relationship between degradation of endogenous macrophage protein and exposure to bacteria at various stages of sporulation was studied. Rabbit pulmonary macrophages were obtained by lavage, attached to plastic tissue culture dishes, and prelabeled with [14C]- or [3H]-phenylalanine for 1 or 20 h, respectively. Bacillus licheniformis (ATCC 14580) was grown in Bacto Marine Broth until at least 50% of the bacilli contained refractile spores (19 h), washed and lyophilized. The lyophilized bacilli were washed, counted and applied for 1.5 h to the washed prelabeled macrophages at a ratio of 300 bacteria/macrophage. Rates of degradation of both rapidly and slowly turning over proteins were increased. The effect was no mediated by soluble components of te incubation medium. Free spores, vegetative cells and autoclaved sporulating bacilli did not affect rates of proteolysis. We propose that proteases from the lyophilized sporulating bacilli participate in endogenous macrophage protein degradation following engulfment.