Genomic typing of class I HLA alleles adds substantially to the success of transplantation of hematopoietic stem cells from unrelated donors, even if the donors are serologically identical to their recipients with respect to HLA-A, B, and DR antigens.

It has been found possible to separate cells according to their surface anti gens by the use of antibody‐coated columns. High efficiency columns were made by double‐layer principles, first coating beads with antigen followed by antibody in excess. Such columns could be shown to contain a high amount of free antigen‐binding sites for the relevant antigens. Lymphoid cells were thus fractionated according to their surface concentration of immunoglobu lin and a highly selective retention of mouse B lymphocytes was observed when filtering spleen cells through an anti‐immunoglobulin column prepared according to the above procedure. No evidence of retention of mouse T lymphoid cells was observed in the same system. By the use of anti‐gamma‐2a immunoglobulin columns, it was found possible to deplete a population from memory cells potentially capable of synthesizing gamma‐2a antibodies. No evidence was found that columns prepared in the described manner would function through combining with receptors on lymphoid cells for antibody‐antigen complexes. By using anti‐A blood group columns, it was possible to selectively retain cells (erythrocytes or kidney cells) with A blood group anti gen on their surface. High‐avidity immune antibodies were found to be more efficient than ‘natural’ anti‐A antibodies in this test. No evidence was found of anti‐A antibodies being adsorbed on to the passing cells as tested by in vitro serological tests and tissue culture experiments. The applications of a technique for separating cells according to their surface antigens are con sidered obvious.

The distribution in the mouse of lymphoid cells carrying receptors for IgG or IgG‐Ag was investigated. B lymphocytes were found to have receptors reacting with both IgG and IgG‐Ag. Resting T lymphocytes did not react with IgG‐Ag. T lymphocytes activated by passage through irradiated, allogeneic mice had a receptor reacting with IgG‐Ag, but not with IgG.

Interferon y (IFN-y) induces HLA-DR and -DQ molecules and causes an accumulation of transcripts in HL-60 cells. Experiments were, therefore, designed to investigate the intracellular signaling molecules regulating the appearance of HLA class II molecules. The expression of HLA class II (DR and DQ) molecules induced by IFN-y was blocked by a calmodulin antagonist, W7, but not by a protein kinase C inhibitor, H7. Furthermore, a direct activator of protein kinase C, phorbol 12-myristate 13-acetate, was unable to induce HLA class II (DR) molecule expression. These results suggest that IFN-y induces HLA class II molecules on HL-60 cells by way of a calcium-calmodulin pathway and not by way of a protein kinase C pathway. Calmodulin is activated by a transient rise in the cytosolic free calcium. In fact, IFN-y evoked a calcium influx into HL-60 cells, whereas depletion of Ca2+ from culture medium resulted in a failure of IFN-y to induce DR expression. Furthermore, the calcium ionophore A23187 by itself induced DR molecule expression. These results suggest that IFN-y stimulates calcium influx by a so-called receptor-mediated calcium channel and activates the calmodulin branch of the culcium messenger system, resulting in the induction of DR molecules on the surface of HL-60 cells.