IFN-γ Is the Only Anti-rotavirus Cytokine Found after In Vitro Stimulation of Memory CD4 + T Cells from Mice Immunized with a Chimeric VP6 Protein

CD4⁺ T cells are the only lymphocytes required for protection of mice against rotavirus shedding after mucosal immunization with chimeric VP6 (MBP::VP6) and the adjuvant LT(R192G). One possible effector of protection is CD4⁺ T-cell cytokines. To determine if memory CD4⁺ T cells of immunized mice produce cytokines with direct anti-rotavirus activity, an in vitro infection model was developed using mouse CMT-93 cells and rhesus rotavirus (RRV). Spleen and lamina propria (LP) cells, as well as purified splenic CD4T cells obtained after intranasal immunization of BALB/c mice with MBP::VP6/LT(R192G) released large quantities of two cytokines (IL-17 and IFN-γ) into cell supernatants when stimulated with MBP::VP6. Production of these same cytokines is rapidly upregulated in intestinal lymphocytes after rotavirus inoculation of immunized mice. IL-17 pretreatment of CMT-93 cells had no effect on subsequent RRV replication, but IFN-γ was the most potent inhibitor within a panel of nine cytokines tested. Supernatants obtained after in vitro stimulation of splenic CD4⁺ T cells of immunized mice had high levels of anti-RRV activity and their pretreatment with mAb against IFN-γ caused essentially complete loss of activity. Thus, IFN-γ was the only cytokine identified in stimulated CD4⁺ T cells from immunized mice that directly inhibited rotavirus replication.