Do CD2 and CD3-TCR T-cell activation pathways function independently?

T cells can be activated either through the CD3-T-cell receptor (TCR) complex or through CD2 (the sheep erythrocyte receptor) via an 'alternate' pathway. A number of studies have suggested that these pathways are linked. Here, Dieter Kabelitz discusses recent advances in understanding the mechanism of T-cell activation, focusing on findings that indicate that certain T cells do not express CD2. The identification of CD2-negative T cells opens a new approach for studying the interrelationship between CD3-TCR and CD2 T-cell activation pathways.