Newborns, in particular preterm neonates, suffer a high frequency of microbial infections. MAIT cells are innate-like T cells expressing a semi-invariant Vα7.2-Jα33 TCR which recognises MR1-restricted, microbial-derived riboflavin (vitamin B2) metabolites unique to bacteria and yeast.
We studied 151 newborns admitted in the Neonatology Department at Robert Debré Hospital divided into four groups according to gestational age (group 1: 24–27 wks; group 2: 28–31 wks; group 3: 32–36 wks; group 4: >37 wks). The rate and kinetics of MAIT cell expansion and maturation were determined longitudinally at birth (day 0), day 3, day 30 and day 60. We performed multiparametric 10-colour flow cytometry analyses using combinations of antibodies to CD45, CD3, CD4, CD8, TCR Vα7.2, CD161, CD45RA, TCR Vα24 and TCRγδ on 100 ml residual whole blood (left over of blood count), allowing characterisation of MAIT cells in parallel with other non-conventional and conventional T cells.
Our results show that the frequency of MAIT at birth is low and significantly differs according to gestational age (median at D0 group 1: 0.21%; group 2: 0.14%; group 3: 0.12%; group 4: 0.06%).
Of note, this frequency remains relatively stable over the first 2 months of life. However, the phenotype of MAIT cell changes after birth with rapid maturation and increased proportion of CD8aa cells. Significant difference was observed between high preterm neonates with and without maternofetal infection. Analysis of MAIT cell frequency in 20 twin pairs showed it was very similar, suggesting that it might be controlled by a genetic and/or early environmental factor.
In conclusion, the frequency of MAIT cells at birth is inversely correlated with gestational age, and is correlated with the presence of maternofetal microbial infection in preterm neonates. Whether it may reflect the presence of microbial products in amniotic liquid, and/or differences in the gut microbiota immediately after birth is under investigation.