Lack of variation in alpha gal expression on lymphocytes in miniature swine of different genotypes

Background: Gal alpha l-3Gal epitopes (alpha Gal) have been demonstrated to be present on tissues of all pig breeds tested to-date and are the major t arget for human anti-alpha galactosyl (alpha Gal) antibodies. We investigat ed members of an MHC-inbred miniature swine herd to assess whether there wa s an association between genotype and expression of aGal. Identification of a low expressor genotype would potentially enable selective breeding of pi gs that might prove beneficial as donors in clinical xenotransplantation. M ethods: we measured alpha Gal expression on various pig cells by use of flu orescent-activate cell sorter (FACS) using (i) purified human anti-alpha Ga l antibody and (ii) the isolectin GS-I-B4. Initial studies were on porcine peripheral blood mononuclear cells (PBMCs) and subsequent studies on lympho cytes, platelets, and T cell subsets (CD4 + and CD8 + cells). Results: ther e was considerable day-to-day variation in alpha Gal expression on PBMCs fr om the same pig. When only lymphocytes were examined, there was a high degr ee of reproducibility, and no significant difference in alpha Gal expressio n was detected between representative pairs of animlas of three different g enotypes. Purified anti alpha Gal antibody bound to different sites on the alpha Gal epitope than did Griffonia (Bandeiraea) simplicifolia I-B4 (GS-I- B4). Lectin binding was significantly reduced in the absence of divalent ca tions. When CD4 + and CD8 + T cells were examined for alpha Gal expression, two distinct populations of each type of cell were observed, with larger c ells expressing a higher level of aGal. Conclusions: although the number of pigs of different genotypes studied was small, on the basis of this limite d study, pigs of a low aGal expressor genotype that could be selectively br ed for use in clinical xenotransplantation were not identified.