Monocytes respond to recombinant HCC-4. Recombinant HCC-4 was used at the indicated concentrations in (A) microchemotaxis assays with human monocytes (□) and THP-1 cells (•) or (B) Ca²⁺ flux assay with THP-1 monocyte cells. The results shown are representative of three independent experiments. The chemotatic index (number of cells migrated/background) was calculated from the total cell count of five high power fields (1,000× at eyepiece) from duplicate wells. For calcium flux, the reponse of THP-1 cells to a HCC-4 concentration of 10⁻⁷ mol/L is shown. Desensitization by RANTES was at the same concentration. Flux buffer alone was used as a negative control. The results are displayed as the ratio of emmission 400:490 nm versus time.