Transplantation in miniature swine. VIII. Recombination within the major histocompatibility complex of miniature swine

Offspring of heterozygous parents derived from three herds of miniature swine, each of which is homozygous at the major histocompatibility complex (MHC), were screened for recombination within the MHC. The swine were typed serologically at weaning and later typed by mixed lymphocyte reaction (MLR). Two intra-MHC recombinants were discovered, both of which involved the exchange of D region specificities without apparent dissociation of ABC region specificities, confirming the localization of the SLA-D region outside of the SLA-ABC regions. The first recombinant was the offspring of an SLAc/d (cd) by dd mating and typed serologically as cd but typed by MLR as dd. The second recombinant was the offspring of a cd by cd mating. It typed serologically as cc but stimulated cc in one-way MLR and retained its reactivity to dd, thus suggesting a possible recombination within the D region. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of 3H-leucine-labeled lymphocyte surface antigens demonstrated that corresponding Ia antigens were also exchanged during these recombinant events supporting the hypothesis that genes coding for Ia antigens are identical or closely linked to D region genes encoding the MLR specificities.