= Rosette assay
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.<The Human Rosette-Forming Cell as a Marker of a Population of Thymus-Derived Cells by Joseph Wybran and others>[Abstract, sheep erythrocyte rosettes and participant range]{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>.<Anti-Mac-1 selectively inhibits the mouse and human type three complement receptor by D. I. Beller and others>[Abstract, selective inhibition of rosetting]{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.
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