Previously fatal murine ehrlichiosis due to HF strain (derived from infected mouse spleen homogenate) infection is associated with T cell-mediated tissue damage, high levels of serum TNF-α and IL-10, and CD4-Th1 hyporesponsiveness (Stevenson et al., 2008), which are associated with liver pathology and failure to clear HF strain in mice (Ismail et al., 2004). This evidence concerns the gene CD4 and infection.