A similar paradigm was observed for infection with the Gram-negative intracellular pathogen Francisella tularensis, wherein studies using T cell depletions or T cell knockout mice have demonstrated that while mice that have lost either CD4+ or CD8+ T cells are able to clear an initial or challenge infection, the loss of both CD4+ and CD8+ T cell subsets impairs bacterial clearance and protective memory responses [29,37,38]. The gene discussed is CD4; the disease is infection.