α2,6 sialylation distinguishes a novel active state in CD4 and CD8 cells during acute infection.

Toxoplasmosis is a worldwide parasitosis that is usually asymptomatic; cell-mediated immunity, particularly T cells, is a crucial mediator of the immune response against this parasite. Membrane protein expression has been studied for a long time in T lymphocytes, providing vital information to determine functional checkpoints. However, less is known about the role of post-translational modifications in T cell function. Glycosylation plays essential roles during maturation and function; particularly, sialic acid modulation is determinant for accurate T cell regulation of processes like adhesion, cell-cell communication, and apoptosis induction. Despite its importance, the role of T cell sialylation during infection remains unclear. Herein, we aimed to evaluate whether different membrane sialylation motifs are modified in T cells during acute infection using different lectins. To this end, BALB/c Foxp3 mice were infected with , and on days 3, 7, and 10 post-infection, splenocytes were obtained to analyze conventional (Foxp3) CD4 and CD8 populations by flow cytometry. Among the different lectins used for analysis, only lectin, which detects sialic acid α2,6 linkages, revealed two distinctive populations (SN and SN) after infection. Further characterization of CD4 and CD8 SN lymphocytes showed that these are highly activated cells, with a TEf/EM or TCM phenotype that produce high IFN-γ levels, a previously undescribed cell state. This work demonstrates that glycan membrane analysis in T cells reveals previously overlooked functional states by evaluating only protein expression.