Eight skin graft donor-recipient pairs were selected by lymphocyte typing for production of HL-A typing antisera. After the second or third skin graft from the same donor, antibodies appeared in the sera of five of the recipients. The antibodies were directed against antigens which seem to be determined by alleles of the LA and 4 sub-loci, and the specificity showed close correlation to the HL-A incompatibility between donor and recipient. By re-immunization with intradermal leucocyte injections, two additional recipients produced antibodies against donor cells. One of these antisera seemed to detect a new HL-A antigen of the 4 sub-locus (called FJH). It is concluded that skin grafting and leucocyte injections is a simple and efficient method for production of HL-A typing antisera of desired specificity. The results also indicate that the remaining alleles of the HL-A system may be identified by antisera obtained by this method.

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Five out of six unrelated persons, grafted three times with skin from a single donor, produced cytotoxic antibodies against donor lymphocytes. Two antisera appeared to be monospecific, and the three other antisera contained antibodies of limited specificity. The iso-specificities of the antisera showed good correspondence to the incompatibility in the HL-A locus detected between donor and recipient by the group specific lymphocytotoxic antisera used. It is concluded that some strong skin cell antigens can be detected by lymphocyte typing that are of importance in the production of cytotoxic iso-antibodies; it may therefore be possible to select suitable skin graft donor-recipient pairs for production of lymphocytotoxic antisera of limited and desired iso-specificity.

By immunization within specially selected donor-recipient pairs it was possible to produce antibodies against three new HL-A antigens. One of these was later found identical to Dal7, the other two are called Li of the LA series, and LND of the Four series of antigens. The antigens behaved in population and family studies as if they were determined by alleles at the LA and Four sub-loci. The present status of the HL-A system seems to be that 8 La alleles and 9 Four alleles are well defined. However, unknown HL-A antigens of low frequency still remain to be identified. The reported method seems to be very useful for this purpose.

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