Glycopeptidolipids for evaluating the role of non-tuberculous mycobacteria in latent tuberculosis infection diagnosis

A disagreement between TST and IGRAs was reported in non-BCG vaccinated children population. The role of non-tuberculous mycobacteria (NTM) sensitisation in latent tuberculosis infection (LTBI) diagnosis had been studied using NTM sensitins. Although in some cases a NTM sensitin positive response was observed, due to the reported cross-reaction with some Mycobacterium tuberculosis antigens, a true LTBI can not be rejected. The aim was to study the role of NTM in LTBI diagnosis using Mycobacterium avium complex specific glycopeptidolipids (GPLs). 38 individuals were classified in five groups: study group (6 non-BCG vaccinated children with discordant results: positive TST and negative T-SPOT.TB), negative healthy individuals (8 children with a negative TST and T-SPOT.TB), 16 paediatric LTBI patients (positive both TST and T-SPOT.TB), 6 patients with M. avium complex infection microbiologically confirmed and 2 children with active TB. PBMCs were isolated from each individual and stimulated with M. avium serovar 4 GPLs. The presence of sensitised T-cells against the antigens was analysed by means of ELISPOT in house . From study group individuals, 100% responded to the stimulation with GPLs. Any negative healthy individual showed a positive ELISPOT result after stimulation. The response to GPLs in LTBI individuals was negative in all cases. In valid cases, a positive result in response to GPLs was obtained in patients with confirmed M. avium complex infection (5/5). One of the TB patients responded when stimulated with GPLs. The results reinforce the hypothesis that non-BCG children who respond to TST and have a negative IGRA result, could be sensitised to NTM.