Abstract Body: Coxsackievirus B3 (CVB3) is an enteric virus that is a primary cause of inflammation of the heart muscle, known as viral myocarditis. Viral myocarditis is a significant cause of heart failure, and nearly 40,000 cases are reported each year. Unfortunately, approximately 5% of CVB3 infections are fatal. Unfortunately, no vaccines or drugs are available for this virus. Interestingly, there is a sex bias in viral myocarditis where men are more susceptible than women. Unfortunately, the underlying basis for the sex bias in infection is incompletely understood. We recently determined that T cells play an essential role in CVB3 clearance using a novel oral inoculation mouse model. Here, we show a sex difference in the CD4⁺ T cell response to CVB3 that is important in limiting viral pathogenesis. We found that CVB3 induced CD4⁺ cell expansion in female mice but not in male mice. CVB3 infection also led to the expansion of CD62L^lo CD4⁺ T cells in the mesenteric lymph node and spleen of female but not male mice as early as five days post-inoculation, indicative of activation. Using a recombinant CVB3 virus expressing a model CD4⁺ T cell epitope, we found that the expansion of CD4⁺ T cells in females is viral-specific and not due to bystander activation. Finally, the depletion of CD4⁺ T cells before infection led to enhanced mortality, indicating that CD4⁺ T cells protect against CVB3 in female mice. We are also currently investigating the impact of CD4⁺ T cell subtypes, and the role of intestinal T cells play in limiting intestinal CVB3 replication and dissemination. These data demonstrate that CVB3 induces a CD4⁺ T cell response in female mice and highlight the importance of sex-specific immune responses to viral pathogens.