Augmentation of NK activity by Corynebacterium parvum fractions in vivo and in vitro

Biochemically modified whole cell preparations and derived fractions of Corynebacterium parvum (C. parvum) were evaluated for the ability to augment natural killer cell cytoxicity in vivo and in vitro in rats. Unfractionated C. parvum enhanced peritoneal cell (Pc) NK activity in a dose dependent fashion. This activity appeared to be enriched in insoluble light residue material obtained from hot phenol water extraction. Enhancement of Pc cytotoxicity was significantly greater at all time points tested in rats injected with light residue when compared to rats injected with comparable amounts (by dry weight) of unfractionated organisms. In addition, pyridine extractable material and HCl modified preparations were capable of boosting Pc NK activity following intraperitoneal (I.P.) injection. Periodate treatment abrogated C. parvum's ability to boost Pc cytotoxicity and insoluble residue material obtained from pyridine extraction was likewise devoid of NK-enhancing properties. Culture of rat spleen cells overnight with unfractionated C. parvum, light residue and pyridine residue materials enhanced NK cytotoxicity whereas HCl and periodate modified whole cell preparations as well as phenol and pyridine extractable material were incapable of boosting cytotoxicity in vitro. In vitro augmentation by culturing with light residue was dependent on the presence of adherent cells in rat spleen cell populations. Pyridine extracts boost cytotoxicity in vivo and have no effect in vitro while the opposite is true of pyridine residue material suggesting different mechanisms of NK augmentation by C. parvum between in vitro and in vivo systems.