Lack of variation in alphaGal expression on lymphocytes in miniature swine of different genotypes

Gal(alpha)1-3Gal epitopes (alphaGal) have been demonstrated to be present on tissues of all pig breeds tested to-date and are the major target for human anti-(alpha)galactosyl (alphaGal) antibodies. We investigated members of an MHC-inbred miniature swine herd to assess whether there was an association between genotype and expression of alphaGal. Identification of a low expressor genotype would potentially enable selective breeding of pigs that might prove beneficial as donors in clinical xenotransplantation.

we measured alphaGal expression on various pig cells by use of fluorescent-activated cell sorter (FACS) using (i) purified human anti-alphaGal antibody and (ii) the isolectin GS-I-B4. Initial studies were on porcine peripheral blood mononuclear cells (PBMCs) and subsequent studies on lymphocytes, platelets, and T cell subsets (CD4+ and CD8+ cells).

there was considerable day-to-day variation in alphaGal expression on PBMCs from the same pig. When only lymphocytes were examined, there was a high degree of reproducibility, and no significant difference in alphaGal expression was detected between representative pairs of animlas of three different genotypes. Purified anti-alphaGal antibody bound to different sites on the alphaGal epitope than did Griffonia (Bandeiraea) simplicifolia I-B4 (GS-I-B4). Lectin binding was significantly reduced in the absence of divalent cations. When CD4+ and CD8+ T cells were examined for alphaGal expression, two distinct populations of each type of cell were observed, with larger cells expressing a higher level of alphaGal.

although the number of pigs of different genotypes studied was small, on the basis of this limited study, pigs of a low alphaGal expressor genotype that could be selectively bred for use in clinical xenotransplantation were not identified.