Isolation and characterization of macrophage phagosomes containing infectious and heat-inactivated Chlamydia psittaci: Two phagosomes with different intracellular behaviors

Abstract

Infectious Chlamydia psittaci enters macrophages via a cytochalasin B-insensitive pathway in which chlamydia-containing phagosomes do not fuse with lysosomes; heat-inactivated C. psittaci enters macrophages via a route in which phagosomes do fuse with lysosomes. In an attempt to explain these differences, phagosomes containing infectious and heated chlamydiae were isolated from mouse macrophages by a procedure developed to isolate L-cell chlamydial phagosomes by rate zonal centrifugation. Macrophage phagosomes acted similarly to L-cell phagosomes on dextran and discontinuous sucrose gradients and exhibited similar detergent sensitivities. Total proteins of the two phagosomes were compared with each other, L-cell proteins, and surface-labeled proteins from macrophages. Both macrophage phagosome membranes had at least nine poteins with equal sodium dodecyl sulfate-polyacrylamide gel electrophoresis mobilities; some were the same as L-cell phagosome proteins. Each phagosome had at least one protein not seen in the other. Only two phagosome proteins had mobilities equal to macrophage plasma membrane proteins. Macrophage phagosomes containing infectious and heat-inactivated C. psittaci, although created by different entry mechanisms and destined for different intracellular fates, exhibited only a few differences in their proteins.