 CD11b

CD11b is the alphaM protein subunit that pairs with CD18 to form the integrin Mac-1. It is useful as a molecular identifier on several myeloid-cell populations, including neutrophils, but its detection alone does not measure receptor activation or prove one unique cell identity. The whole receptor contains both chains.

A 1990 study tested Mac-1 binding to ICAM-1 using purified proteins and engineered cells in reciprocal arrangements. Cells carrying one partner attached to a surface carrying the other, and appropriate monoclonal antibodies inhibited the interaction. Additional experiments examined stimulated neutrophil attachment to stimulated endothelium.^[ref]

Reciprocity is illuminating: if cells bind a purified surface in one orientation, an unintended cell component might still contribute. Reversing which partner is on the surface and controlling expression supplies another test of the proposed pairing. The result supports a specific Mac-1/ICAM-1 contribution under the tested conditions, rather than claiming that every CD11b-bearing cell adheres identically in every environment.