Lack of lysosomal fusion with phagosomes containing Ehrlichia risticii in P388D1 cells: abrogation of inhibition with oxytetracycline.

Fusion of lysosomes with phagosomes containing Ehrlichia risticii, an obligate intracellular parasite, was evaluated in P388D1 murine macrophagelike cells. Lysosomes in cells ranging in infectivity from 30 to 70% were labeled cytochemically with acid phosphatase or via endocytosis of thorium dioxide or cationized ferritin to document phagosome-lysosome (P-L) fusion in untreated cells and cells treated with oxytetracycline. Regardless of the marker used, P-L fusion was generally not observed in E. risticii-containing vacuoles in untreated cells, while significantly greater P-L fusion with ehrlichia-containing vacuoles was observed after oxytetracycline treatment. When latex beads were introduced into uninfected cell cultures, P-L fusion was observed with vacuoles containing latex. Fusion of lysosomes with latex-containing vacuoles in cells was significantly greater than fusion of lysosomes with ehrlichia-containing vacuoles in the same infected cells. These findings indicate that E. risticii is able to inhibit P-L fusion, whereas oxytetracycline deprives organisms of this ability.