New approach to management of malignant ascites with streptococcal preparation OK-432. III. OK-432 attracts natural killer cells through a chemotactic factor released from activated neutrophils.

When a streptococcal preparation, OK-432, was administered intraperitoneally to patients with malignant ascites, lymphocytes with cytotoxic activity against tumor cells increased in number in the peritoneal cavity after 5 to 7 days. To investigate the underlying mechanisms of such lymphocyte accumulation, lymphocyte chemotactic activity (LCA) in ascitic fluid was measured by a modification of the Boyden method. High LCA was found on the third and fourth days after the OK-432 injection. This LCA was generated in the cell-free supernatant of the patients' abdominal neutrophils that accumulated in the peritoneal cavity 24 hours after the injection of OK-432. A similar LCA was also found when normal peripheral neutrophils were incubated with OK-432. Incubation of normal neutrophils without OK-432 failed to generate LCA, however, and OK-432 alone had no LCA. We tentatively named this factor "neutrophil-derived lymphocyte chemotactic factor" (NDLCF). The NDLCF was heat stable and nondializable, and its molecular weight was approximately 45,000 daltons. It attracted mainly natural killer cells by immunoperoxidase assay of migrated lymphocytes in the chemotactic membrane. These characteristics were distinct from C5a, interleukin-1, and interleukin-2. The results suggest that the newly found NDLCF may be responsible for the infiltration of cytotoxic lymphocytes, especially natural killer cells in the peritoneal cavity in patients with malignant ascites when treated by intraperitoneal injections of OK-432.