Unglycosylated Mtaa expresses an Mtab-like determinant

Antigenic polymorphism of the class I-like maternally transmitted antigen (Mta) is controlled by a maternally transmitted factor (Mtf) thought to reside in mitochondria. However, the mechanisms by which Mtf generates antigenic polymorphism are not known. To address this issue, we investigated a possible role of post-translational oligosaccharide addition in the formation of Mta determinants. We examined the expression of Mta on cytotoxic T lymphocyte (CTL) target cells cultured in tunicamycin (TM), a known inhibitor of asparagine(N)-linked glycosylation. Of 18 Mta^b-specific CTL lines, 8 lysed TM-treated Mta^a targets. Furthermore, a subclone of one of these eight lines, 17D5.G2, lysed TM-treated targets from all Mta^a strains tested, regardless of H-2K/D haplotype. On the other hand, this CTL clone did not lyse TM-treated target cells from the Mta null, but H-2 expressing strain B10. CAS2. Therefore expression of this Mta^b-like determinant is concordant with the expression of Mta^a and seems unlikely to represent a cross-reactive H-2K/D epitope. Our data suggest that an Mta^b-like determinant is expressed on unglycosylated Mta^a molecules. Thus, N-linked oligosaccharides probably prevent the expression of an Mta^b-like determinant on the Mta^a molecule. We discuss how Mtf may contribute to Mta polymorphism through glycosylation.Abbreviations used in this paper CAB Con A blast - CML cell-mediated lympholysis - Con A concanavalin A - CTL cytotoxic T lymphocyte - DMEM Dulbecco's modified minimum essential medium - FCS fetal calf serum - IL-2 interleukin-2 - LPS lipopolysaccharide - mAb monoclonal antibody - MLC mixed leukocyte culture - mMDM modified Mishell-Dutton medium - Mta maternally transmitted antigen - NK natural killer - sMDM supplemented Mishell-Dutton medium - TM tunicamycin - ₂m beta-2 microglobulin