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 (Kd 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 4 nM) and low affinity for NAP‐2 ( K d ≥700 nM), whereas the type B receptor was of equally high affinity ( K d 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. J. Leukoc. Biol. 55: 763‐770; 1994.