Failure of IgG production due to a defect in the opening of the chromatin structure of Iγ1 region in a patient with IgG and IgA deficiency

Patients with common variable immunodeficiency (CVID) display reduced levels of two or all three of the major immunoglobulin isotypes, and the deficiency is characterized by failure of B cells to differentiate into plasma cells in many cases. A patient (14 years old, female) showed normal serum IgM levels and low serum IgG and IgA levels, including low levels of all IgG subclasses. Northern blot analysis suggested that the patient's B cells may be defective at the immunoglobulin heavy chain isotype switch. The germ-line C gamma 1 transcript was amplified from cDNA of healthy controls by the addition of recombinant IL-2 (rIL-2) to pokeweed mitogen-stimulated peripheral mononuclear cells or Staphylococcus aureus Cowan I (SAC)-stimulated IgM-producing lymphoblastoid cell lines (LCL) transformed by Epstein-Barr virus, while it was not amplified from cDNA of the patient. In the I gamma 1 region of LCL cultured with SAC plus rIL-2, the inner cytosine in the 5' C-C-G-G 3' sequence nearest the 3' site of the I gamma 1 region, at least, was not completely unmethylated in the patient. Moreover, the DNase I hypersensitive site was not induced in the patient's LCL by SAC plus rIL-2. These results indicate that the defects of the immunoglobulin heavy chain isotype switch in the patient's B cells are due to failure in the synthesis of germ-line C gamma transcripts, and this may be caused by defects in opening of the chromatin structures of specific switch regions.