A positive AHG T cell crossmatch between an untransfused male recipient and non-beaded spleen cells from the donor is most likely due to?

A positive AHG (anti-human globulin) T cell crossmatch indicates that there is an immune reaction between the recipient's serum and the donor cells, which suggests that the recipient has antibodies that recognize antigens on the donor T cells. In this scenario, a non-beaded spleen cell sample is involved, which could contain a variety of immune cells, including macrophages.

Macrophage contamination is a significant consideration because these cells can express a variety of surface molecules that may not be present on the intended T cell population. If macrophages are present in the spleen cell preparation, they could introduce additional antigens that the recipient's immune system recognizes as foreign. This recognition can lead to a positive crossmatch, even if the recipient has not been previously sensitized to specific T cell antigens. Hence, the presence of macrophages may cause a false positive reaction in the AHG crossmatch by involving non-specific interactions.

In contrast, the other choices may relate to different immunological interactions but do not specifically explain the result of a positive T cell crossmatch in this context. For instance, specific antibodies against HLA molecules or other antigens typically relate to more conventional sensitization scenarios, but as the recipient in this case is untransf