HL--A typing in Northern Ireland 1971-74.

FOR the past few years the policy in most transplantation centres has been to allocate cadaver kidneys to recipients whose tissues are antigenically similar to the donor's. Tissue similarity has been assessed by comparison of the HL-A antigens identifiable on lymphocytes i(not kidney or other tissue cells) from donor and recipient. The technique of HL-A typing is not in itself difficult. Briefly, lymphocyte suspensions are prepared from freshly drawn peripheral blood by flotation on a Triosil-Ficoll solution (Harris and Ukaejiofo, 1969). After washing with buffered saline, the suspensions are added to tissue typing plates which have been primed with sera and covered with liquid paraffin to prevent evaporation. Each plate has spaces for up to 72 sera. After incubation, complement, in the form of a mixture of rabbit and human serum, is added to each test and a further incubation carried out. In those tests where lymphocyte antigens have reacted with the sera, complement activation results in cell death. Microscopic examination after the addition of trypan blue (which stains the killed cells but is excluded from living ones) enables positive tests to be identified. In common with most of the tissue typing laboratories in Great Britain, we receive our sera from the National Tissue Typing Reference Laboratory (N.T.T.R.L.) in Bristol. This has the advantage that donors and recipients throughout Britain are, in the main, typed with the same sera. The HL-A antisera in use are mainly obtained from women during pregnancy who become immunised to HL-A antigens inherited by the foetus from the father. Antibody-containing sera are identified by the same basic method as for HL-A typing, except that cells of known antigen content from a panel of volunteers (members of staff) are tested against sera of unknown antibody content. Most tissue typing laboratories, including our own, carry out a screening programme on pregnancy sera as part of their routine work. Potentially useful sera are submitted to N.T.T.R.L. who carry out further tests, and may request further supplies of the test sera. In parallel with the antibody screening programme, serum samples from prospective kidney recipients are also tested. This is of importance, since antibodies in a recipient's serum may cause immediate rejection of an incompatible transplant. They are in general weak antibodies, and are difficult to characterise.