Analysis of immunoglobulin E V-H transcripts in a bronchial biopsy of an asthmatic patient confirms bias towards V(H)5, and indicates local clonal expansion, somatic mutation and isotype switch events

Immunoglobulin E (IgE)-dependent mechanisms play a pivotal role in mediatin g allergic disease. Previously, V-H-C epsilon transcripts from blood or spl een of atopic asthmatics have been analysed for V-H gene usage and patterns of somatic mutation. An over-representation of the minor V(H)5 family has been observed, consistent with a superantigen drive. As local mucosal event s in IgE production may be more significant in the disease process, we have analysed V-H-C epsilon transcripts from a bronchial biopsy of a patient wi th severe asthma. V(H)5 predominance was confirmed with 10 of 30 unique clo nes derived from this family. Repeated sequences, some with intraclonal var iation, revealed clonal expansion and continuing mutational activity at the site. Unexpectedly, three unmutated V-H-C epsilon sequences were found, in dicating that isotype switching to IgE can occur without mutation. Detectio n of a sister clone with extensive mutations was again consistent with loca l mutational activity. Evidence for local isotype switching was obtained by identification of clonally related immunoglobulin M (IgM), immunoglobulin G (IgG) and immunoglobulin E (IgE) sequences. However, in contrast to findi ngs in blood, no IgG4 transcripts clonally related to IgE were detected, su ggesting that the balance between synthesis of IgG4 and IgE may differ betw een systemic and local sites. These data confirm. a V(H)5 bias in IgE, and support the concept that IgE-synthesizing B cells arise via local different iation.