Ligation of CD4 Concomitant to Activation Induces Primary CD4+T-Cell Adhesion and Pseudopodia Formationin Vitro

A regulatory function for CD4 molecules in lymphocyte adhesion and motility was investigated. Murine splenic CD4+T cells, activated in the presence of phorbol ester and immobilized anti-CD4 mAb, adhered to the plastic surface and formed extended cytoplasmic projections (pseudopodia). Pseudopod formation was cell-density-dependent, peaked at Day 3, and disappeared by Day 5 in culture. This response could be inhibited by soluble anti-CD4 and by RGD-containing peptide. Ligation of CD4 was required at a late stage in cell activation, and stimulated cell motilityin vitro.Addition of IL-4, but not IL-2, upregulated pseudopod formation induced by suboptimal stimuli. Anti-IL-4 mAb blocked pseudopod formation, and exogenous IL-4 restored the response. A combination of IL-4 plus phorbol ester, but not IL-2 plus phorbol ester, induced pseudopod formation in concert with CD4 ligation. Exogenous IL-2, on the other hand, blocked pseudopod formation. CD45RBlowCD4+T cells were much more efficient than CD45RBhighCD4+T cells for pseudopod formation. These results indicate that CD4 ligation induces CD4+T-cell adhesion and motility, mainly in the memory/activated subset, which might be relevant for immune responsesin vivo.