Upon incubation of M. hominis or M. arthritidis for 2 hr with rabbit peritoneal exudate granulocytes or leukocytes from human peripheral blood, no killing of mycoplasma was observed either in the presence or absence of type-specific antiserum. However, ¹⁴CO₂ production from glucose-1-¹⁴C was stimulated up to 10-fold in the presence of live or heat-killed PPLO. The extent of stimulation depended upon the number of organisms and the presence of type-specific antiserum. The stimulation of ¹⁴CO₂ production seems not because of tight adherence of PPLO to the leukocytes, since PPLO were quantitatively recovered in the medium after sedimenting the granulocytes.

The enhanced conversion of medium lysolecithin to cellular lecithin that accompanies phagocytosis of polystyrene particles was significantly reduced when PPLO were also present. Mycoplasma alone elicited no stimulation of lecithin formation.

Killing of E. coli, a microorganism readily engulfed and killed by leukocytes in vitro, was diminished when the leukocytes were preincubated with mycoplasma.

These findings indicate that M. hominis and M. arthritidis are not ingested by granulocytes to any detectable extent, but that these organisms affect the leukocytes' metabolism and also impair phagocytosis of E. coli.