MONOMER-DIMER EQUILIBRIA OF INTERLEUKIN-8 AND NEUTROPHIL-ACTIVATING PEPTIDE .2. EVIDENCE FOR IL-8 BINDING AS A DIMER AND OLIGOMER TO IL-8 RECEPTOR-B

By chemical cross-linking experiments we show that at physiologically relevant concentrations IL-8 and NAP-2 monomers are in an equilibrium with dimers and even oligomers (K-D similar to 300-800 nM). Oligomerization seems to be more prevalent for IL-8 than for NAP-2. The form in which IL-8 and NAP-2 bind to their specific receptors was analyzed in binding experiments with COS-1 cells expressing IL-8 receptor A or B in recombinant forms. Both receptors were cloned from the human myeloid leukemic cell. line AML-193. Type A receptor had high affinity for IL-8 (K-D similar to 4 nM) and low affinity for NAP-2 (K-D greater than or equal to 700 nM), whereas the type B receptor was of equally high affinity (K-D similar to 2 nM) for both IL-8 and NAP-2. However, IL-8 receptor B could bind specifically three to four times more IL-8 than NAP-2, and NAP-2 was a weak competitor for IL-8 binding to the same receptor. In addition, IL-8, but not NAP-2, could be cross-linked to dimers when bound to IL-8 receptor B. We suggest from these findings that IL-8, but not NAP-2, binds as a dimer and oligomer to IL-8 receptor B.