Evidence for abnormally regulated alternative RNA processing of mu chain gene in B-lymphoblastoid cells from Bloom's syndrome.

Selective IgM deficiency is commonly found in patients with Bloom's syndrome. In this study, mu mRNA synthesis was investigated in B-lymphoblastoid cells transformed by Epstein-Barr virus (LCL) from a patient with Bloom's syndrome who showed selective IgM deficiency. LCL established from the patient with Bloom's syndrome well expressed IgM molecules in their surface, but scarcely produced secreted IgM, compared with healthy controls. The JH hybridization patterns of digested DNA of LCL from the patient with Bloom's syndrome showed the rearrangement of VDJ as well as those of control LCLs. The mu mRNA was well detected, but mu s C-terminal mRNA was poorly detected compared with control LCLs, indicating that secreted mu mRNA was poorly transcribed though membrane-bound mu mRNA was well transcribed. These results suggest that alternative RNA processing of mu chain gene is abnormally regulated in LCL from patients with Bloom's syndrome.