Interaction between endothelium and CD4⁺CD45RA⁺ lymphocytes: Role of the human CD38 molecule

CD38 is a type II transmembrane glycoprotein which is widely used as a marker for immature and activated lymphocytes, as well as plasma cells. Although its functional role and natural ligand are not known, CD38 has been shown to transduce activation signals to lymphocytes. Our work shows that CD38 is preferentially expressed by CD4⁺CD45RA⁺ cells, but not by CD4⁺CD45RO⁺ cells. CD4⁺CD45RA⁺ cells are reported to respond poorly to stimuli acting through the CD3/TCR in vitro and to display unique migration pathways in vivo. Cross-linking of CD38 by mAb did not overcome the hyporesponsiveness of CD4⁺ resting/naive cells to several activation stimuli. In contrast, CD38 engagement by mAb specifically inhibited their binding with human vein endothelial cells. These data suggest that CD38 may play a role in lymphocyte migration. The same inhibitory effect was detected on the (human x mouse) hybrid cell line CP410.A10, which expresses human CD38, but not on its CD38 subclone CP14. CD38 mAb did not inhibit the conventional binding assay between endothelium and several human CD38⁺ T and B cell lines. However, the inhibition was apparent when the binding assay was performed at 4°C on a rocking shelf, conditions that minimized integrin function. These data suggest that CD38 mediates weak cell binding to endothelium, which is effective even in dynamic conditions. These features are reminiscent of those exerted by selectins, which are adhesion molecules that account for leukocyte rolling on vascular endothelial cells and play an important role in lymphocyte homing.