Differentiating between memory and effector CD8 T cells by altered expression of cell surface O-glycans

Currently there are few reliable cell surface markers that can clearly disc riminate effector from memory T cells. To determine if there are changes in O-glycosylation between these two cell types, we analyzed virus-specific C D8 T cells at various time points after lymphocytic chlorio-meningitis viru s infection of mice. Antigen-specific CD8 T cells were identified using maj or histocompatibility complex class I tetramers, and glycosylation changes were monitored with a monoclonal antibody (1B11) that recognizes O-glycans on mucin-type glycoproteins. We observed a striking upregulation of a speci fic cell surface O-glycan epitope on virus-specific CD8 T cells during the effector phase of the primary cytotoxic T lymphocyte (CTL) response. This u pregulation showed a strong correlation with the acquisition of effector fu nction and was downregulated on memory CD8 T cells. Upon reinfection, there was again increased expression of this specific O-glycan epitope on second ary CTL effectors, followed once more by decreased expression on memory cel ls. Thus, this study identifies a new cell surface marker to distinguish be tween effector and memory CD8 T cells. This marker call be used to isolate pure populations of effector CTLs and also to determine the proportion of m emory CD8 T cells that are recruited into the secondary response upon reenc ounter with antigen. This latter information will be of value in optimizing immunization strategies for boosting CD8 T cell responses.