In a study assessing response to M. tuberculosis specific antigens among 590 HIV positive patients in Denmark using the Quantiferon-TB In Tube test, the proportion of patients with indeterminate test results due to low IFN-γ production following PHA stimulation was significantly higher in patients with low CD4 count (<100 cells/ml) compared to those with high CD4 cell count (> 100 cells/ml), and the median IFN-γ release was significantly lower in those persons with a low CD4 cell count compared with patients with a high CD4 cell count [29]. This evidence concerns the gene CD4 and tuberculosis.