The active rosette mixed-lymphocyte reaction: an early marker of lymphocyte activation linked to HLA-D-DR differences.

A new approach to rapidly determine human mixed-lymphocyte culture (MLC) is presented. It is based on the identification of an early increase in the percentages of active T rosettes (TEa) in the MLC tubes. Active T rosettes represent a subset of T cells with high-avidity receptors for sheep red blood cells. All subjects tested had a full determination of their HLA-A, -B,-C, and -D-DR. The following observations were made: (1) When the MLC was done between 10 pairs of fully HLA-A,-B,-C, and -D-DR incompatible subjects, a highly significant increase (P less than 0.001) was observed after 2 hr of MLC in all pairs tested. (2) The same increase was observed in all 10 pairs of identical HLA-A,-B, and -C subjects but not sharing HLA-D-DR antigens. (3) In the cases of HLA-D-DR semi-identity, the increase in TEa percentages was less marked after 2 hr of culture (P less than 0.05) and delayed in time to reach the significance level of P less than 0.001 after 4 hr of culture. (4) In contrast, in the case of full HLA-D-DR identity, no increase in TEa percentages was observed at any time in the culture (2, 4, and 24 hr and 4 days) in nine pairs of subjects tested (two pairs of identical twins). In conclusion, these results indicate that the active T rosette MLC is a rapid approach (2 hr) to evaluate HLA-D-DR differences without influence by HLA-A,-B, or -C. As such it is an early marker for HLA-D-DR determination and may become a useful tool in the field of human histocompatibility to study the HLA-D-DR region.