The Previously Defined R^d Class I Molecule is a Non-ß₂M Associated Conformational Variant of L^d

Abstract

Post-translational differences between murine class I molecules were compared. As determined in a pulse-chase experiment, the rate of N-linked oligosaccharide processing of L^d molecules was found to be 4–5 times slower than that of D^d, K^d or D^dml molecules. Furthermore, the relative molar ratio of ß₂m to class I was found to be significantly lower with L^d than with D^d, K^d or D^dml molecules. Thus, both the slower processing and weaker ß₂m association correlate with the previously reported lower cell surface expression of L^d compared to D^d, K^d or D^dml molecules. Since Ddml is a chimeric D^d/L^d molecule these results demonstrate that the amino terminus of the class I molecule influences processing, ß₂m-association and cell surface expression.

The R^d molecule was initially defined by sequential immunoprecipitation using anti-L^d reactive mAbs 30–5–7 (α2 specific) and 28–14–8 (α3 specific). In contrast to L^d, the R^d molecule is only positive with mAb 28–14–8. In this communication we demonstrate that both L^d and R^d are products of the H-2L ^d gene using an H-2L ^d gene transfectant. Furthermore, the 30–5–7^- L^d molecule (Rd) was found not to be ß2m associated, in contrast to the 30–5–7⁺ L^d molecule where ß₂m was readily apparent. As much as 40% of the biosynthetically-labelled L^d molecules were found in this non-ß₂m associated conformation. Thus, these studies suggest that L^d molecules have several unique properties that could all be related to an aberrant ß₂m association. These properties include slower oligosaccharide processing, lower cell surface expression and detection of a non-ß₂m associated conformational variant.