TCR transgenic mice specific for a major CD4+ T cell epitope (VP272–86) of TMEV restricted with I-As (018030, SJL.Cg-Tg (TcraTcrbVP2) 1 Bkim/J from the Jackson Laboratory) have been used to investigate the differentiation of CD4+ T cell types during viral infection [65,136]. The gene discussed is CD4; the disease is viral infectious disease.