Human T cell activation induces the expression of a novel CD45 isoform that is analogous to murine B220 and is associated with altered O-glycan synthesis and onset of apoptosis.

Activated T cells undergo changes during their transition to T cell blasts and, subsequently, via a phase of anergy, to apoptosis. For example, activated murine T cell blasts express the B-cell-specific CD45R isoform, B220, a marker also present on T cells in mice and humans with defective Fas-mediated apoptosis in vivo, suggesting a role for B220 up-regulation in the transition of activation to apoptosis. Human T cells, activated in vitro with superantigens and mitogens, also express B220 as they undergo blastogenesis and cell cycle progression. B220 expression peaks on T cells undergoing apoptosis. CD43-hexasaccharide glycoform expression and lectin binding profiles indicate that B220 expression is reflective of altered O-linked glycan biosynthesis found in specific T cell subsets transitioning through the phases of proliferation, anergy, and apoptosis. Potential implications of these alterations include changes in lymphocyte adhesion and trafficking and homeostasis through altered sensitivity to Fas-dependent and independent pathways of apoptosis.