Interestingly, while no statistically significant differences were observed in the numbers of innate immune cells present in the lungs, we showed that total numbers of CD4+ T and CD8+ T cells and the numbers of virus-specific CD8+ T cells were significantly reduced following infection with MAp2009, indicating that virulence of this virus could be attributed to an impaired cytotoxic response. The gene discussed is CD4; the disease is infection.