Lack of correlation between lymphocyte activating determinants and HLA-DR on acute leukaemias.

The expression of allogenic lymphocyte-activating determinants (LAD) on 25 acute leukaemias has been compared with the expression of cell-surface antigens identified by HLA-DR allo- and xeno-antisera. The close correlation between LAD and DR known to occur on normal lymphocytes was not found in leukaemias. Twenty-two LAD+ leukaemias included 2 DR- cases, whilst 2 LAD- leukaemias were DR+. With the exception of 3 leukaemias all were strongly beta 2 microglobulin+. No correlation was found between the % DR+ cells and the level of lymphocyte stimulation. Separation of leukaemia cells on Ficoll gradients into fractions containing different proportions of DR+ cells did not correlate with LAD expression. Furthermore, antisera to DR antigens only partially blocked leukaemic LAD. The results support the notion that LAD on acute leukaemias are not necessarily associated with or identical to HLA-DR antigens, and that the lymphocyte activating capacity of HLA-DR may be modulated.