MORPHOLOGICAL-STUDY OF CYTOTOXICITY PRODUCED BY PSK-INDUCED POLYMORPHONUCLEAR LEUKOCYTES (PMNS) AND NOCARDIA-RUBRA CELL-WALL SKELETON

The morphologic changes in PMNs induced by an i.p. injection of PSK, a polysaccharide from the mycelia of Coriolus versicolor, and tumor cel ls undergoing cell death, were evaluated by immunohistochemical staini ng and electron microscopy. Male C3H/He mice, 8-10-weeks old, received an i.p. injection of 125 mg/kg of PSK. Their PMNs were obtained 6 h a fter the PSK injection by peritoneal lavage. N-CWS (Nocardia rubra cel l wall skeleton) was added at the start of the chromium release assay using the MM46 mammary carcinoma cell line, which is syngeneic to C3H/ He mice, as target cells. During the cytotoxic assay, the cells were f ixed at various time points. The MM46 cells expressed ICAM-1 while the PMNs expressed both ICAM-1 and LFA-1 as determined by immunohistochem ical staining and immunoelectron microscopy using anti-ICAM-1 and anti -LFA-1 antibodies. PMNs with ruffle-like microvilli adhered to the MM4 6 tumor cells 30 min after the addition of N-CWS. Immunoelectron micro scopic findings suggested that the adhesion molecules were LFA-1 on th e PMNs and ICAM-1 on the MM46 tumor cells, but cell fusion between the PMNs and tumor cells was not observed. The MM46 tumor cells gradually lost their microvilli, which showed cell damage, and died 6-7 h after the addition of the N-CWS. This time course of tumor cell death is co mpatible with the results of the cytotoxic assay. Pretreatment of PMNs by anti-LFA-1 antibody suppressed % lysis of MM46 tumor cells from 90 % to 10% (p < 0.01). These data suggest that adhesion molecule on the surface of PMNs such as LFA-1 might play an important role on signal t ransduction of these PMNs cytotoxic function in this experimental syst em.