Codominant expression of the polymorphic MICA alloantigens encoded by genes in the HLA region

MOLINERO, LUCIANA LORENA; MARCOS, CINTIA YANINA; MIRBAHA, FARIBA; FAINBOIM, LEONARDO; STASTNY, PETER; ZWIRNER, NORBERTO WALTER

EUROPEAN JOURNAL OF IMMUNOGENETICS

Blackwell Publishing Group

Lugar: Oxford, UK; Año: 2002 vol. 29 p. 315 - 320

0960-7420

The HLA related, polymorphic MICA (MHC class I related chain A) gene encodes for a 383 amino acid polypeptide, with three extracellular domains (a1, a2, and a3), a transmembrane region, and a cytoplasmic tail. We have previously shown that freshly isolated endothelial cells, fibroblasts, keratinocytes, and monocytes express MICA, while peripheral blood CD4+, CD8+ or CD19+ lymphocytes do not. This polymorphic MICA molecule is a target for specific alloantibodies in sera from kidney, heart and lung transplant recipients, even though its possible role during graft rejection remains to be demonstrated. In this study we addressed whether there is codominance in the expression of MICA. We isolated RNA from a heterozygous cell line (HCT116), previously shown by sequencing-based typing to be MICA*001/MICA*00902, as well as 12 clones derived from it. Thereafter, we retrotranscribed the RNA into cDNA, and performed a molecular typing using MICA-sequence specific oligonucleotides (SSOP). Using this approach, we detected the RNA encoding MICA*001 and MICA*00902 in all the clones and in the parental cell line, indicating that MICA is codominantly expressed. This codominant expression was further confirmed by cloning and sequencing plasmids encoding these two alleles produced from the same HCT116 RNA preparation. We also produced the two recombinant MICA proteins (MICA*001 and MICA*00902). They reacted with rabbit anti-MICA polyclonal antibodies by ELISA and Western blot, indicating that the plasmids carrying the cDNA inserts probably encode for functional MICA proteins. This strongly suggests that, like the HLA class I and class II proteins, MICA is codominantly expressed. The codominant expression of the polymorphic, HLA-like MICA alloantigens may have implications in the immune response elicited by the allograft in organ transplantation.