REDUCED EXPRESSION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I FREE HEAVY-CHAINS AND ENHANCED SENSITIVITY TO NATURAL-KILLER-CELLS AFTER INCUBATION OF HUMAN LYMPHOID LINES WITH BETA-2-MICROGLOBULIN

Enhancement of major histocompatibility complex (MHC) class I expressi on leads to protection from recognition by natural killer (NK) cells i n several systems. MHC class I gene products can be expressed in diffe rent forms at the cell surface - for example as ''empty'' beta2-microg lobulin (beta2M)-associated heterodimers or free heavy chains. To stud y the role of different class I heavy chain forms in NK target interac tions, we have used lymphoblastoid target cell lines preincubated with beta2m. This was found to shift the equilibrium between beta2m-associ ated and nonassociated - heavy chains in favor of the former. In paral lel, there was a significant increase in NK sensitivity.The recognitio n of MHC class I-deficient cell lines was not affected by beta2m, argu ing against a general nonspecific effect Of beta2m on NK sensitivity. Our data indicate that protection against NK recognition correlates wi th target cell expression of free heavy chains (i.e. devoid Of beta2m) rather than with expression of complexes.