CLASS-II-ANTIGEN-NEGATIVE PATIENT AND MUTANT B-CELL LINES REPRESENT AT LEAST 3, AND PROBABLY 4, DISTINCT GENETIC-DEFECTS DEFINED BY COMPLEMENTATION ANALYSIS

Expression of class II major histocompatibility complex antigens in defective B-lymphoblastoid cell lines from patients with class II antigen deficiency and from in vitro mutants generated with the same phenotype was studied. By heterogenetic fusion experiments, at least three, and probably four, complementation groups were defined. Furthermore, clone 13 (a DR-, DP-, but DQ+ cell line) appeared to belong to the RJ2.2.5 complementation group, for which all other members are DR-, DP-, and also DQ-. Thus, it is hypothesized that the cell lines of this group lack the activity of a gene that can differentially regulate the DR/DP and the DQ promoters.