To differentiate anti-Fy3 from anti-Fy5, which cell type should be tested?

To differentiate anti-Fy3 from anti-Fy5, it is crucial to use a cell type that can express the appropriate glycoproteins involved in the Fy antigen system. Testing on a cell line that is Fy(a+b+) and Rh null provides the best opportunity to reveal the specificity of the antisera since both Fy3 and Fy5 are associated with different aspects of the Fy antigen system.

In this scenario, Fy(a+b+) cells possess both the Fy(a) and Fy(b) antigens. When tested against anti-Fy3, these cells will remain reactive, whereas anti-Fy5 will likely show a unique reaction pattern, allowing for the differentiation between the two antibodies. Rh null cells are particularly useful as they lack the Rh antigens entirely, providing a clearer context for observing the interactions specifically related to Fy antigens without interference from Rh-related reactions.

In summary, using Fy(a+b+), Rh null cells offers the best means of differentiating these two antibodies because it leverages their unique characteristics without the obfuscating influence of Rh antigens that might be present in other cell types. Other options either do not express the appropriate combination of antigens or are subsets that do not exhibit the necessary reactivity for this differentiation.