Role of ab and gd T Cells in the Host Response to Salmonella Infection as Demonstrated in T-Cell-Receptor-Deficient Mice of Defined Ity Genotypes

Salmonella spp. are facultative intracellular bacteria which enter the body through the intestinal tract. We studied the roles of T cells expressing either the a and b chains or the g and d chains of the T-cell receptor (ab T cells or gd T cells, respectively) in the host defense against Salmonella using mice genetically deficient in either ab T cells, gd T cells, or both T-cell subsets. These mutant strains of mice were infected orally or intraperitoneally with Salmonella dublin, and the progression of the disease was monitored by determining bacterial numbers in the feces, gut wall, Peyer’s patches, mesenteric lymph nodes, spleen, and liver. Since susceptibility to Salmonella infection in mice is strongly affected by the alleles at the Ity locus, T-cell-mutant mice with either the Ity-sensitive or Ity-resistant phenotype were tested for resistance to S. dublin infection. We found that even though large numbers of intraepithelial and mucosal ab and gd T cells populate the normal intestine, they have no role in controlling the invasion of S. dublin into the intestine or the subsequent bacterial replication in the Peyer’s patches or gut wall. Furthermore, systemic infections were equally severe for the first 6 days in normal, ab T-cell-deficient, and gd T-cell-deficient mice, and ab but not gd T cells were required for clearance of S. dublin, regardless of the Ity phenotype. However, mice that lacked both T-cell subsets had higher bacterial counts in their livers 15 to 18 days after infection than did ab T-cell-deficient mice, suggesting that gd T cells can contribute to acquired immunity to S. dublin.