Local and Systemic Cell-Mediated Immunity against Transmissible Gastroenteritis, an Intestinal Viral Infection of Swine

Abstract

The occurrence of local and systemic cell-mediated immunity (CMI) in swine against transmissible gastroenteritis (TGE) virus, a coronavirus that infects the epithelial cells of the small intestine of swine, has been investigated. Leukocyte suspensions prepared from intestinal lamina propria (LP) and spleen were each incubated with and without inactivated TGE virus. The supernatants from these cultures were tested for the presence of macrophage migration inhibition factor (MIF) by the indirect MIF test using guinea pig peritoneal exudate cells as the source of macrophages. All swine serologically negative for TGE antibodies (i.e., unexposed to TGE virus) were also negative for MIF. Fourteen of 15 swine orally exposed to TGE virus 6 to 30 days before assaying for CMI gave a positive test for MIF production by both LP and splenic lymphocytes. The 15th animal, orally exposed to TGE virus 27 days before assaying, was negative for MIF production by both LP and splenic lymphocytes. In nine of nine of these orally exposed animals where LP and splenic leukocyte suspensions were prepared so as to contain equal numbers of lymphocytes, the percentage of inhibition of migration by supernatants from LP preparations was significantly greater (p ≤ 0.01) than by supernatants from spleen preparations. Two of three animals orally exposed to TGE virus 7 to 9 ½ months before assaying for CMI were negative for MIF production by lymphocytes from both sources. In 10 of 10 animals given TGE virus subcutaneously, MIF production by splenic lymphocytes was significantly greater (p ≤ 0.01) than by LP lymphocytes, and in 9 of 10 of these animals MIF production by LP lymphocytes was negligible (percentage of inhibition of migration < 3%).