Attachment and ingestion of gonocci by human neutrophils

Abstract

Previous studies have indirectly shown that type 1 gonococci are most resistant to phagocytosis by human neutrophils (PMN) than type 3 gonococci. Using phase contrast, fluorescent, and light microscopy, the authors directly quantitated PMN gonococcal interaction, with emphasis on separating ingestion from attachment. PMN monolayers were incubated on slides with type 1 or type 3 gonococci. The slides were iced to stop phagocytosis and stained with anti gonococcal fluorescent antibody (FA). After methanol fixation, the FA stained gonococci associated with PMN were counted. Since the live PMN excludes FA, the FA stained gonococci represent only extracellular gonococci. Methylene blue was then added to the same slide to stain both ingested and surface attached gonococci. Using these methods, intracellular and extracellular cell associated gonococci were quantitated under varying conditions. The numbers of methylene blue stained cell associated gonococci were similar for types 1 and 3. The proportions of cell associated gonococci that were ingested were: with normal serum, 3.7 ± 4.1% for type 1 and 56.2 ± 3.5% for type 3 (P < 0.001); with heat inactivated serum, 1.0 ± 3.0% for type 1 and 52.6 ± 3.7% for type 3 (P < 0.001); with high titer anti gonococcal antibody serum, 4.8 ± 4.3% for type 1 and 64.0 ± 1.6% for type 3 (P < 0.001). Thus, most type 3 organisms were ingested, but most type 1 gonococci were bound on the PMN surface.