Chronic myelogenous leukemia‐derived basophilic granulocytes express a functional active receptor for the anaphylatoxin C3a

The receptor for the inflammatory peptide C3_a has scarcely been examined on human cells. This work demonstrates that human tumor‐derived basophilic granulocytes express C3_a receptors, and presents parts of the hitherto unknown C3_a‐signal transduction. When incubated with IL‐3, these cells specifically liberated histamine on C3a stimulation. Independent from IL‐3, 240000 ± 100000 receptors per cell with a K_d of 5.6 ± 0.9 nM were determined. (Ca²⁺)j increased from 120 ± 35 nM to 300 ± 80 nM after a C3_a challenge, as measured by digital imaging fluorescence microscopy, and rested at its basal level in the presence of C3_a‐desArg, the immediate catabolic product of C3_a in vivo. This (Ca²⁺ )_i increase could be completely desensitized homologously by C3_a as well as inhibited by up to 75% by pertussis toxin. Thus, tumor‐derived basophils are suitable for cloning of the human C3_a receptor.