Compared to the radiologically normal lobes in the same individuals, a lower baseline number of IFN-γ-expressing CD4+ cells can be observed in the BAL fluid recovered from the sites of tuberculous cavitation, with a weaker IFN-γ production in response to tuberculin stimulation [31], suggesting that the composition of Th1 cells in BAL may provide valuable information on the progression of TB. The gene discussed is CD4; the disease is tuberculosis.