Abstract

On activation of human basophilic granulocytes with anti-IgE or with the chemotactic peptide, formyl-methionyl-leucyl-phenylalanine, the expression of the CD63 antigen on the cell surface, detected by monoclonal antibody (MAb) 435, increased up to 100-fold. The kinetics of CD63 up regulation and histamine release were identical, and a strong correlation was found between percentage of MAb 435-binding basophils and extent of histamine release. Immunoelectronmicroscopy demonstrated that the epitope for MAb 435 in resting basophils is located on the basophilic granule membrane. After basophil activation, MAb 435 bound to the exterior of the plasma membrane. Experiments with various doses of anti-IgE demonstrated that the binding of MAb 435 to basophilic granulocytes follows an all-or-nothing-like response per cell. Basophils either do not bind the MAb at all, or they bind a maximal amount of the MAb. We also measured the up regulation of the CD11/CD18 leukocyte adhesion complex. Here, too, we noted an increase in cell-surface exposure of all subunits after activation. This increase was not as strong as increase found with MAb 435. Thus, MAb 435 is an interesting new tool for investigating the activation of human basophils, in addition to the measurement of mediator release. This MAb may be useful for the detection of basophil activation in vivo.