MAIT and Tuberculosis in children : a different behavior from adults.

Mucosal associated invariant T cells (MAIT) are innate T lymphocytes that display a semiinvariant T cell receptor capable of recognizing bacteria derived riboflavin metabolites. MAIT cells could contribute to the early control of infection with Mycobacterium Tuberculosis. The aims of this study are to determine MAIT cells frequency and phenotype in children with latent or active pulmonary tuberculosis, in comparison with children with pneumonia, or children without infection. The percentage of MAIT cells in the peripheral blodd samples of 24 latent tuberculosis, 33 patent tuberculosis, 20 pneumoniae, 37 inflammatory disease, 76 children with contact without infection, 67 children without disease were determined by flow cytometry. As frequency of MAIT slowly increase still five years old, we divised the children in two groups: less than five years or five years old. No difference was observed between the different groups under 5 years. On the other hand, as for adults, percentages of MAIT cells were significantly lower in children more than 5 years with patent tuberculosis than health children (mean ± SD : 2,14% ± 1,87 versus 3,04 ± 1,96 ; p= 0,0168). To identify if the low frequency was the consequence of a migration in infected lung, we look after the frequency of MAIT in eleven bronchoalveolar lavage and compare to the blood. The percentage of MAIT cells was twice as low in the BAL as in the blood. Interestingly the expression of CD69, a marker of activation, is six times higher in the LBA than in the peripheral blood. In conclusion the results for children in tuberculosis are different to adults. In children the infection with Mtb usually appear in one way, in contrary to adult wich is a reactivation.