Binding of α-defensins to human CD4. (A) Competition of synthetic α-defensin-1 (○) and α-defensin-2 (•) with the anti-CD4 mAb Leu3a for binding to plastic-immobilized recombinant sCD4 in ELISA. The plates were coated with sCD4 at 5 μg/mL; α-defensins were added prior to Leu3a and kept in the wells throughout the reaction period. (B) Effect of synthetic α-defensin-2 on binding of different anti-CD4 mAbs to sCD4 with various epitope specificity (indicated on the x-axis) in ELISA. The assays were performed as in panel A. The epitope specificities of the anti-CD4 mAbs are indicated below. D indicates domain; CDR, complementarity-determining region. All antibodies were used at 1 μg/mL; α-defensin-2 was used at 7.3 μM. Error bars indicate SD of mean values obtained from 3 repeated assays.