CD4 and infection: When comparing the pulmonary and extrapulmonary bacterial burden in TCRβ−/− and C57Bl/6 WT mice before and after CD4+ T cell transfer, it was observed that in contrast to WT mice, TCRβ−/− mice had about one log higher bacillary load in the lung, spleen, and liver at day 30 after infection, which could be due to the absence of T-cell response, which otherwise is essential for effective elimination of M.tb from the host.