Characterization of CD31 expression on murine and human neonatal T lymphocytes during development and activation

BACKGROUND: CD31, expressed by the majority of the neonatal T cell pool, is involved in modulation of T-cell Receptor signalling by increasing the threshold for T cell activation. Therefore, CD31 could modulate neonatal tolerance and adaptive immune responses. METHODS: Lymphocytes were harvested from murine neonates at different ages, human late preterm and term cord blood, and adult peripheral blood. Human samples were activated over a five-day period to simulate acute inflammation. Mice were infected with influenza; lungs and spleens were harvested at days 6 and 9 post-infection and analyzed by flow cytometry. RESULTS: CD31 expressing neonatal murine CD4(+) and CD8a(+) T cells increase over the first week of life. Upon in vitro stimulation, human infants’ CD4(+) and CD8a(+) T cells shed CD31 faster in comparison to adults. In the context of acute infection, mice infected at 3-days old have an increased number of naive and activated CD31(+) T lymphocytes at the site of infection at day 6 and 9 post-infection, as compared to 7-days old; however, the opposite is true in the periphery. CONCLUSION: Differences in trafficking of CD31(+) Cytotoxic T Lymphocytes (CTLs) during acute influenza infection could modulate tolerance and contribute to a dampened adaptive immune response in neonates.