Expression of the CD2 Activation Epitope T11‐3 (CD2R) on T Cells in Rheumatoid Arthritis, Juvenile Rheumatoid Arthritis, Systemic Lupus Erythematosus, Ankylosing Spondylitis, and Lyme Disease: Phenotypic and Functional Analysis

CD2R is an activation‐associated epitope unmasked by a conformational change of the CD2 cell‐surface glycoprotein. In spite of elaborate studies on the role of CD2 and CD2R in adhesion and stimulation of T cells in vitro, no instances of CD2R expression in vivo were known to date. We report high levels or CD2R observed on blood and synovial fluid T cells in rheumatoid arthritis and on peripheral blood T cells in juvenile rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis, and Lyme disease. In vivo, expression of CD2R was restricted to T cells, not limited to a particular T‐cell subset and not correlated with the expression of p55 interleukin 2R (IL‐2R) (CD25) or major histocompatibility complex (MHC) class II molecules. When stimulated to prolieration via CD2 or CD3, ex vivo CD2R+ T cells showed the same basic activation requirements as CD2R‐ T cells.