CD4 and tuberculosis: We speculate that the decreased frequency of M. tuberculosis CD4+ T cells may be offset by an influx of CD4+ T cells that normalizes the absolute number of M. tuberculosis–specific CD4+ T cells and thus keeps the tuberculosis risk relatively low, thus resolving the apparent discrepancy between a substantially decreased M. tuberculosis–specific CD4+ T-cell frequency but only a doubling of tuberculosis risk in early infection [5].