Cholera toxin transiently inhibits porcine T cell proliferation in vitro

Cholera toxin (Ctx) is an important mucosal adjuvant with potential experimental applications in pigs. However, little is known about the direct effects of Ctx on porcine immune cells. Therefore, we analysed the influence of Ctx on mitogen-induced lymphocyte proliferation. Ctx inhibited peripheral blood mononuclear cell (PBMC) proliferation with an IC50 of 34+/-17 ng/mL. This inhibition was not due to increased cell death. Lymphoblast formation in cultures stimulated with concanavalin A and Ctx was decreased at 24 h, but had reached the levels of control cultures again at 72 and 120 h, indicating that suppression was transient. Analysis of T cell subsets revealed that Ctx treatment specifically reduced the percentage of CD4-CD8+ and gammadelta T cells, whereas the proportion of CD4+CD8- increased. Furthermore, Ctx caused secretion of IL-10 by PBMC cultures, but depressed TNFalpha secretion.