FUNCTIONALLY CONFORMED FREE CLASS-I HEAVY-CHAINS EXIST ON THE SURFACE OF BETA(2) MICROGLOBULIN NEGATIVE CELLS

Cytotoxic T lymphocytes (CTL) can recognize antigenic peptides bound in a groove formed by the alpha-1 and alpha-2 domains of the heterodimeric major histocompatibility complex class I molecule. Proper assembly, transport, and stability of functional class I molecules is thought to require beta-2 microglobulin (beta-2m), the light chain of the class I heterodimer. We show here that the requirement for beta-2m is not absolute. Beta-2m- cells can be stained by the D(b) alpha-1 domain-specific B22-249.1 monoclonal antibody, which detects a conformation-dependent epitope. Furthermore, beta-2m- Con 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 beta-2m cells. Finally, we present evidence that a subset of properly conformed H chains, free of beta-2m, may have almost equal representation on beta-2m+ and beta-2m- cells.