DEFINITION OF A NOVEL COMPLEMENTATION GROUP IN MHC CLASS-II DEFICIENCY

In this study we analyzed fibroblasts derived from an MHC class II def iciency patient (type III bare lymphocyte syndrome). Northern blot ana lysis showed that upon induction with IFN-gamma these fibroblasts did not express HLA class TI genes and displayed a strongly reduced level of HLA class I gene expression when compared with fibroblasts of a hea lthy individual. However, when analyzed by RT-polymerase chain reactio n (PCR), residual expression could be detected for HLA-DRA, DPB, and D OA, but not for HLA-DRB, DPA, and DQB. The lack of HLA-DRB transcripts in the patient fibroblasts and the high degree of sequence polymorphi sm of HLA-DRB were exploited in the further analysis of these fibrobla sts. Thus far, at least three, and probably four, complementation grou ps have been defined among patient-derived and experimentally-derived MHC class II-negative cell lines. Transient heterokaryons between the patient fibroblasts and representative B-lymphoblastoid cell lines fro m each of the complementation groups were analyzed by RT-PCR and South ern blotting, using HLA-DRB-specific primers and biotin-labeled sequen ce specific oligonucleotides, respectively. These analyses showed that the fibroblasts of this particular patient belonged to a novel comple mentation group in MHC class II deficiency.