In vivo degradation of gonococcal outer membrane proteins within human leukocyte phagolysosomes

We previously showed in vitro hydrolysis of outer membrane proteins by lysosomal proteases and purified elastase. In this study we examined the in vivo relevance of the previous studies. Outer membranes were obtained from Neisseria gonorrhoeae type 3 (strain GC7) by LiCl2 extraction. Some preparations were labeled with 125I. Phagocytizable particles were prepared by coating latex beads with outer membranes, and polymorphonuclear leukocytes were allowed to phagocytize serum-opsonized particles. After homogenization of neutrophils, phagolysosomes were recovered by flotation through sucrose. Phagolysosomes were prepared for slab gel electrophoresis immediately or incubated further at 37 degrees C to allow continued degradation of outer membrane proteins. The principal protein (protein I) and minor proteins (proteins II) of outer membranes were hydrolyzed in whole neutrophils and in isolated phagolysosomes. Proteins II were more susceptible to hydrolysis than protein I. Hydrolytic products formed were nearly identical in vivo and in vitro. We also radiolabeled the surface-exposed proteins of live gonococci. Degradation of outer membrane proteins on the intact bacteria within neutrophil and monocyte phagolysosomes was shown. This indicates that our earlier in vitro model is relevant to in vivo hydrolysis of gonococcal outer membrane proteins.