Binding characteristics of radioiodinated crystal-induced chemotactic factor to human neutrophils

The binding of radiolabeled crystal-induced chemotactic factor (CCF) to human neutrophils is characterized. Binding of 125I-CCF to the cells was higher at 4 degrees C than at 24 degrees or 37 degrees C and was found to be independent of CA2+ and Mg2+ ion concentration. The binding showed a pH optimum of 6.0. Tosylamido phenylethyl chloromethyl ketone at 100 mumol/L concentration inhibited 20% of 125I-CCF binding, but phenylmethylsulfonyl fluoride at 200 mumol/L had no effect. Approximately 50% of cell-associated 125I-CCF was released after treatment with proteases. The nonspecific uptake by the cells, as measured by the uptake of 3H-sucrose and 14C-inulin in the presence of CCF, was negligible. After the steady-state binding of 125I-CCF to the cells, approximately 15% of the cell-associated radioactivity at 4 degrees C and 40% to 50% at 24 degrees and 37 degrees C was released into the medium after 60 minutes of incubation in medium alone. Dissociation of the radioactive material was not affected by the presence of tosylamido phenylethyl chloromethyl ketone or phenanthroline in the media. The dissociated material was determined to be degraded 125I-CCF, suggesting that degradation of 125I-CCF occurs after binding to its specific receptor on the human neutrophil.