In the analysis of potential associations between immune activation and CD4 lymphocytopenia we observed that plasma neopterin levels showed a significant inverse correlation to CD4 cell count for both HIV+/TB patients (SR rho -0.35, p<0.001) and for HIV-/TB patients (SR rho -0.51, p<0.001), see S1 Fig. This evidence concerns the gene CD4 and tuberculosis.