Interaction of gonococci with phagocytic leukocytes from men and mice

The interaction of human and mouse phagocytic leukocytes with representative virulent (F62-T1) and avirulent (F62-T4, RD-5) strains of Neisseria gonorrhoeae was studied in vitro. Leukocyte monolayers were incubated with gonococci for 30 min at 37 C, washed repeatedly, reincubated with fresh medium, and sampled for viable bacteria at intervals. After the initial incubation period and washing, human leukocytes retained larger numbers of viable T1 than of T4. During the subsequent 120 min of incubation, the numbers of viable T1 remained approximately constant, whereas viable counts of T4 declined by about two-thirds. In contrast, mouse leukocytes under similar conditions destroyed 70% of both types of gonococci. When human bactericidal serum was applied to infected human leukocytes, it had no effect on T4 but inactivated over 50% of T1. It is concluded that T4 are phagocytized by human leukocytes and are thus exposed to internal digestion, but are protected from bactericidal serum. T1, on the other hand, either adhere to the surface of the leukocytes or remain located so that they are neither digested by the leukocytes nor protected from bactericidal serum.