Qa-12--a novel determinant of activated T and B lymphocytes

Investigation of the antigenic phenotype of activated lymphocytes using the broadly cross-reactive mAb 6.3.4 revealed two phenotypic alterations as compared with the resting lymphocytes. The Qa specificity Qa-m208 disappears after lectin activation of Qa-m208-positive T lymphocytes. Analysis of Q7 and Q9 transfectants expressing the Qa-2 polypeptides shows that Qa-m208 is an epitope of the Qa-2 antigen. Because the Qa-2 antigens are still expressed on T lymphoblasts which have lost Qa-m208, changes of the Qa-2 molecules occur and result in the loss of certain epitopes. The second phenotypic change that we observed is the appearance of a novel specificity, Qa-12. Its expression is induced by lymphocyte activation and it is expressed on lymphoblasts of both T and B cell origin. The presence of this novel non-ubiquitous antigenic specificity is determined by the Tla region.