Additional analysis of antigen-specific Interleukin-2 release does not improve the performance of IGRAs for the differentiation of different states of mycobacterium tuberculosis infection

Introduction Discrimination of tuberculosis (TB) from latent infection with Mycobacterium tuberculosis (LTBI) by immunodiagnostic assays remains challenging. This study compares the performance of a novel two color FluoroSpot with an established interferon-γ (IFNγ) release assay (IGRA) EliSpot. We hypothesize that additional information of Mtb-specific interleukin (IL)-2 release will improve the immunodiagnosis of different stages of Mtb-infection. Methods Immune responses of peripheral blood mononuclear cells were assessed using EliSpot and FluoroSpot test systems in 18 culture confirmed pulmonary TB cases, 41 healthy controls (24 - LTBI), and 10 persons with known cured TB. The number of IFNγ spot forming cells in EliSpot was compared with IFNγ in FluoroSpot, furthermore IL2 + or IFNγ + IL2 + producing T-cells were determined. Results IFNγ response in EliSpot and FluoroSpot showed a good correlation (ESAT6 r 2 =0,67; CFP10 r 2 =0,73). Against to expectations, the analysis of IL2 + and IFNγ + IL2 + cells did not improve differentiation between TB, LTBI and cured TB substantially. The number of single IFNγ + IL2 - producing cells was significantly higher in patients with TB compared with LTBI controls (ESAT6-induced p=0,013) as well as in patients with TB compared with former TB patients (CFP10-induced p=0,006). However a big overlap of test results hampers to distinguish between the cohorts. Conclusion EliSpot and FluoroSpot results correlate well with each other, however separate analysis of IL-2 and IFNγ secretion by antigen specific T-cells does not allow differentiation of TB from LTBI in clinical practice.