Polysialic acid is expressed in human naïve CD4+ T cells and is involved in modulating activation

The activation of human naïve CD4+ T cells, responsible for orchestrating the immune response, has been reported to cause increased de novo sialylation and overexpression of the genes coding for polysialyltransferases ST8SiaII and ST8SiaIV, suggesting the potential of CD4+ T cells to synthesize polysialic acid (PSA), a type of glycosylation not previously described in these cells. PSA has been found as a post-translational modification in a limited number of mammalian proteins, having a very relevant role in modulating interactions due to its characteristic biophysical properties. In this work, we confirm that human CD4+ T cells express both polysialyltransferases and synthesize PSA, as assessed with the anti-PSA monoclonal antibody (mAb) 12E3. The expression of PSA in resting cells was found restricted to a cell subpopulation (PSA+), that after anti-CD3/anti-CD28 mAbs mediated activation, increased in percentage and mean fluorescence intensity (MFI) expression. Additionally, through ST8SIAII and ST8SIAIV-silencing and by measuring the mRNA of IL-2, IL-2R and IFN-γ, we show that PSA is involved in modulating the activation response of CD4+ T cells.