Functionally Conformed Free Class I Heavy Chains Exist On The Surface Of 32 Microglobulin Negative Cells

Cytotoxic T lymphocytes (CTL) can recognize antigenic peptides bound in a groove formed by the od and ol2 domains of the heterodimeric major histocompatibility complex class I molecule. Proper assembly, transport, and stability of functional class I molecules is thought to require 32 microglobulin (32m), the light chain of the class I heterodimer. We show here that the requirement for 32m is not absolute. 32mcells can be stained by the D b oO domain-specific B22-249.1 monoclonal antibody, which detects a conformation-dependent epitope. Furthermore, 32mCon A blast target cells can be lysed by alloreactive CTL, even in serum-free conditions. Contrary to previous reports, the expression of low levels of conformed D b heavy (H) chains is a property of both normal and transformed 32mcells. Finally, we present evidence that a subset of properly conformed H chains, free of 3zm, may have almost equal representation on 32m + and 32mcells.