Functional and ligand binding specificity of the rabbit neutrophil IL-8 receptor

IL-8 mediates migration and activation of neutrophils. This study describes the functional and ligand binding specificity of the human intercrine peptides IL-8, neutrophil-activating peptide 2 (NAP-2), melanoma growth stimulatory activity (GRO), and platelet factor 4 (PF4) to rabbit neutrophils and mammalian cell lines transfected with rabbit IL-8 receptor cDNA (F3R). Rabbit neutrophil membranes bound ¹²⁵I-labeled IL-8 and ¹²⁵I-labeled NAP-2 but did not bind ¹²⁵I-labeled GRO or ¹²⁵I- labeled PF4. Rabbit neutrophils mobilized intracellular Ca²⁺ in response to IL-8 and NAP-2 but not to GRO or PF4. Monkey kidney cells (COS-7) and hamster lung fibroblasts (CCL-39) were transiently and stably transfected with the rabbit neutrophil IL-8 receptor F3R cDNA. COS-7 cells transfected with F3R cDNA bound ¹²⁵I-labeled IL-8 but did not bind other IL-8-related peptides such as ¹²⁵I-labeled NAP-2, ¹²⁵I-labeled GRO, or ¹²⁵I-labeled PF4. Furthermore, bound ¹²⁵I-labeled IL-8 was only displaced by unlabeled IL-8 but not by unlabeled NAP-2, GROα, or PF4. Consistent with this observation, stably transfected CCL 39 cells expressing F3R cDNA mobilized Ca²⁺ only in response to IL-8. We conclude that F3R cDNA encodes a functional IL-8 receptor isotype with strict ligand binding specificity for IL-8, that rabbit neutrophils do not bind human GROα, and it is suggested that rabbit neutrophils contain in addition to the F3R protein another IL-8 receptor isotype with broad ligand specificity or a distinct NAP-2 receptor.