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D. I. Beller is the first author of a 1982 study relating Mac-1 to a specific function of the complement system. The investigators used an antibody against Mac-1 and a rosette assay, in which appropriately coated red blood cells bind around immune cells. The antibody inhibited binding mediated by the complement fragment iC3b, while selected other receptor-dependent binding remained intact.^[ref]

The controls separated selective inhibition from indiscriminate loss of cell binding. The original conclusion was that Mac-1 was identical to, or closely associated with, the relevant complement-receptor function. A blocking experiment can establish a strong functional association without, by itself, resolving every molecular detail of that association.^[ref]

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. ^[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.^[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.

A rosette assay detects binding by counting cells surrounded by attached red blood cells, producing a flower-like cluster. The attached red cells act as visible binding probes; their coating and the receptor being tested determine what a particular assay measures. A rosette is therefore a measured binding arrangement, not by itself a unique cell identity.

A classic uncoated-sheep-red-cell assay was used to study human lymphocytes. In 1972, Joseph Wybran and colleagues reported rosette-forming cells in blood and thymus, using their distribution as evidence for a thymus-associated population. The blood measurements in 50 normal participants ranged from $4\%$ to $40\%$ under the study conditions.^[ref]

A different design coats red cells with defined complement fragments. In a 1982 experiment, an antibody against Mac-1 inhibited iC3b-dependent rosetting while selected other receptor-mediated binding remained intact. Comparing coatings and inhibition conditions helped connect the binding phenotype to complement receptor 3.^[ref]

For a constructed count, 60 rosette-positive cells among 200 evaluable cells gives $60/200=30\%$. The scoring threshold, denominator and preparation conditions must accompany that percentage: changing what counts as a cluster can change the reported result.

T. A. Springer contributed to experiments connecting immune-cell surface proteins with recognition and cell adhesion. In a 1982 study with D. I. Beller and collaborators, selective antibody blocking related Mac-1 to binding of targets bearing iC3b, a fragment involved in the complement system.^[ref]

With M. L. Dustin, T. A. Springer later investigated how stimulating the T-cell receptor changes adhesion through LFA-1. The 1989 experiments found a rapid, transient increase in adhesion strength. This supplied a mechanism for coordinating target recognition with sticking and subsequent release, rather than treating the presence of an adhesion protein as a fixed measure of how strongly a cell will bind.^[ref]