THE CXC CHEMOKINES GROWTH-REGULATED ONCOGENE (GRO)ALPHA, GRO-BETA, GRO-GAMMA, NEUTROPHIL-ACTIVATING PEPTIDE-2, AND EPITHELIAL CELL-DERIVED NEUTROPHIL-ACTIVATING PEPTIDE-78 ARE POTENT AGONISTS FOR THE TYPE-B, BUT NOT THE TYPE-A, HUMAN INTERLEUKIN-8 RECEPTOR

Interleukin-8 (IL-8), growth-related oncogene (GRO) alpha, GRO beta, G RO gamma, neutrophil-activating peptide-2 (NAP-2), epithelial cell-der ived neutrophil activating peptide-78 (ENA-78), and granulocyte chemoa ttractant protein-2 are potent neutrophil chemoattractants 40-90% iden tical in amino acid sequence that comprise a subgroup of human CXC che mokines defined by the conserved sequence motif glutamic acid-leucine- arginine (ELR). Two human chemotactic receptor subtypes for IL-8, name d IL-8 receptors (IL8R) A and B, have been cloned. They are 78% identi cal in amino acid sequence, coexpressed in neutrophils, and distinguis hed by their different se selectivities for GRO alpha and NAP-2. Their selectivity for other ELR(+) CXC chemokines has not been previously r eported. By measuring calcium flux in human embryonic kidney 293 cells transfected with plasmids encoding IL8RA or IL8RB, we have now define d receptor selectivity for GRO beta, GRO gamma, and ENA-78. The rank o rder of agonist potency, based on inspection of the mean effective con centration values (EC(50)), for IL8RB was GRO gamma (1 nM) > IL-8 (4 n M) similar to GRO alpha (5 nM) similar to GRO beta (4 nM) similar to N AP-2 (7 nM) > ENA-78 (11 nM), and for IL8RA was IL-8 (4 nM) >>> ENA-78 (40 nM) similar to NAP-2 (45 nM) > GRO alpha (63 nM) similar to GRO g amma (65 nM) >> GRO beta. The maximal response of IL8RA to IL-8 was at least a-fold greater than the other five chemokines. All six agonists for IL8RB competed for high affinity I-125-IL-8, -GRO alpha NAP-2, an d -ENA-78 binding sites at IL8RB. GRO alpha, GRO beta, GP gamma, NAP-2 , and ENA-78 competed weakly for the high affinity IL-8 binding site a t IL8RA. Thus, IL8RA and IL8RB are both highly selective for IL-8 and have similar sequences but differ dramatically in their selectivity fo r all other ELR(+) CXC chemokines tested. These findings have importan t implications for developing novel neutrophil-specific anti-inflammat ory drugs directed against the CXC chemokine signaling system.