Mac-1 (source code)
= Mac-1
{c}
= Complement receptor 3
{synonym}
\b[Mac-1], also called complement receptor 3, is an <integrin> <heterodimer> comprising <CD11b> and <CD18>. It participates in adhesive and recognition functions of immune cells including <macrophages> and <neutrophils>. Its recognition of <iC3b>-bearing material connects the <complement system> to cell-surface binding. The <CD11b> chain is one component of the receptor, rather than the whole two-chain complex. https://meshb.nlm.nih.gov/record/ui?lang=en&name=Integrin+alphaM[US National Library of Medicine, CD11b scope note: association with CD18 forms Mac-1]{ref}
The link between an antibody-defined surface marker and complement recognition was tested with a rosetting assay. Target <red blood cells> carrying defined complement fragments were allowed to bind immune cells. Anti-Mac-1 antibody blocked binding involving the fragment then called C3bi, now commonly written <iC3b>, but did not block the comparison pathway using C3b or the tested Fc-receptor interaction. Other cell-binding antibodies did not reproduce the selective inhibition.<Anti-Mac-1 selectively inhibits the mouse and human type three complement receptor by D. I. Beller and others>[Abstract: fragment-defined erythrocytes, macrophage/human polymorphonuclear leukocyte rosetting and specificity controls.]{ref}
The result associated Mac-1 with a particular recognition function rather than merely with a cell lineage. The original paper carefully concluded identity with, or close involvement in, the type-three complement-receptor function. Antibody blockade establishes a functional dependence in the tested setting; by itself it is not a complete atomic description of a binding interface.
Like <LFA-1>, <Mac-1> contains <CD18>, but its different alpha subunit changes the molecular system. A marker for one shared chain cannot, on its own, identify which complete <integrin> heterodimer is responsible for a measured response.
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