Augmentation of Mouse Natural Killer Cell Activity by Lactobacillus casei and Its Surface Antigens

Abstract

L. casei YIT 9018 (LC 9018) augmented the natural killer (NK) cell activity of spleen cells from inbred BALB/c mice injected i.v. with LC 9018 or i.p. with polyinosinate-polycytidylate. Augmentation of this activity by LC 9018 was also observed in male C3H/He, CBA/N and C57BL/6 mice. The spleen cells exhibited no cytolytic activity against P815, a [mouse mastocytoma] cell line insensitive to NK cells. The cytolytic activity of the spleen cells increased 2 days after the injection of 250 .mu.g of LC 9018/mouse, peaked on day 3 and gradually declined thereafter. The increase caused by LC 9018 was also observed in normal and Meth A[mouse cell line]-bearing mice. In vitro treatment with anti-asialo GM1 antibody plus complement completely abrogated the LC 9018-augmented murine NK cell activity. The NK activity on the 3rd day after LC 9018 injection was reduced by in vitro treatment with anti-Thy 1.2 monoclonal antibody plus complement to half of that observed when treatment was with complement alone. There were possibly 2 populations of NK cells in the spleen cell suspension derived from LC 9018-treated mice. One population was asialo GM1-positive and Thy 1-negative, the other asialo GM1-positive and Thy 1-positive.