Figure 8

Recovery of viable intracellular mycobacteria is reduced in Cd36 ^-/- macrophages in an in vitro model recapitulating cellular events in early granuloma formation. Primary "prey" macrophages were incubated with M. marinum and washed to remove extracellular bacteria. Apoptosis was induced by overnight serum starvation, and was evidenced by increased caspase-3/7 activity (data not shown). Control macrophages (no apoptosis) were incubated in media containing 10% fetal bovine serum. Apoptotic primary prey macrophages containing M. marinum were gently scraped and co-incubated with uninfected secondary "predator" macrophages to allow phagocytosis of primary prey macrophages. After washing to remove extracellular apoptotic bodies and bacteria, cells were scraped and plated on mycobacteria culture media for CFU counts. The recovery of viable M. marinum was reduced in systems using Cd36 ^-/- (white bar) relative to Cd36 ^+/+ (black bar) macrophages (*p = 0.0026), suggesting a defect in the uptake of mycobacteria-laden apoptotic macrophages.