The selective depletion of CD4+ cells reduced IFN-γ mRNA expression in the cecal tonsil and intraepithelial lymphocytes and increased production of oocysts of E. tenella in chicks [28, 32], which suggests the important role of CD4+ lymphocytes in controlling primary infection with E. tenella. The selective elimination of CD8+ cells resulted in the exacerbation of disease as evidenced by increased oocyst shedding after secondary infection with E. tenella or E. acervulina [32]. The gene discussed is CD8A; the disease is infection.