Activity of natural killer (NK) cells in the course of experimental trichinellosis in mice

B6C3F1 mice were infected with 200 or 500 larvae of Trichinella spiralis per mouse and pulmonary NK cell-mediated clearance of semisyngeneic tumour cells was determined in vivo on days 10, 20, 30, and 60 after the infection. Cytotoxic activity of NK cells in the lungs was substantially elevated on days 20 and 30 after challenge with both "doses" of the parasite. At the same time large granular lymphocytes (LGLs) as well as cells expressing surface asialo-GM1 molecules were isolated in elevated numbers from spleens of the infected as opposed to the normal mice. Expression of other markers of differentiation, such as THy 1, CD4, and CD8 was also enhanced on splenocytes isolated from the infected mice on day 30 but not 20 after administration of the larvae. The present results indicate that NK cell-mediated activity in vivo is stimulated above the baseline level during migration and early muscle phases of the infection with T. spiralis in mice. The possible impact of this effect upon the course of trichinellosis as well as upon the growth of tumours in the infected host is discussed.