Clonally related IgE and IgG4 transcripts in blood lymphocytes of patients with asthma reveal differing patterns of somatic mutation

Abstract

Isotype switching to IgE contributes to atopic asthma, therefore strategies to divert this process to alternative isotypes could have therapeutic relevance. It is known that patients with allergic disease have serum IgE and IgG4 antibodies with similar specificities, and that cytokines such as IL-4 mediate switching to both of these isotypes. Availability of variable region gene analysis has allowed us to probe isotype variants at the single-cell level. An earlier report described identification in a single atopic patient of short transcripts with a common complementarity-determining region "clonal signature" in combination with C mu, C gamma4 and C epsilon. We have extended this analysis, and have identified V(H)-Cgamma4 transcripts with clear clonal relationship to IgE-derived sequences in blood lymphocytes from three of four patients with atopic asthma. No other IgG subclasses were detected, confirming the link between IgE and IgG4. Full sequences were obtained from each clonally related isotype in all patients, and showed extensive somatic mutation. As previously found for IgE, the IgG4 isotypes had evident intraclonal variation. There were shared mutations between isotypes, but also many differences, indicative of separate cell populations with divergent mutational histories. These findings indicate that, in atopic patients, an individual B cell commonly switches to either IgE or IgG4. Cells producing each isotype then co-exist in the recirculating pool, and the balance between them may influence the disease process.

A Case of Multiple Giant Coronary Aneurysms and Abdominal Aortic Aneurysm Coexisting with IgG4-related Disease

“…The present patient also had a history of bronchial asthma, eosinophilia and elevated serum IgE levels. Regarding a mechanism involving the immunoglobulin isotype switching a previous report demonstrated the clonal relationship of IgE and IgG4 transcription (22). The participation of allergic reactions and the Th2 response, such as the contribution of IL-4 expression in IgG4RD requires further study.…”

IgG4 and IgE Transcripts in Childhood Allergic Asthma Reflect Divergent Antigen-Driven Selection

“…This observation would indicate that, on average, IgG4-producing cells have undergone approximately a third more rounds of cell division than have IgE-producing cells. At first this may appear surprising because IgE-expressing cells can be recruited by secondary class switch from IgG-expressing cells by the so-called "indirect route," IgM→IgG4→IgE, in humans (31,60) or IgM→IgG1→IgE in mice (32) and potentially also from a classical germinal-center pathway (61). One could argue that those IgE-expressing cells that originate from the indirect route should harbor at least as many somatic mutations as their IgG4-expressing precursors (unless cells with fewer somatic mutations are preferentially selected for secondary class switch).…”

“…Xiong et al (32) propose that the indirect route results in potentially pathogenic high-affinity IgE and the direct route results in low-affinity, potentially protective IgE. The presence of clonally related IgG4 and IgE transcripts within blood lymphocytes from individual asthma patients suggests that a major proportion of IgE derives from the indirect route (60,63), although those sequences are not necessarily related by direct switching, as both IgE and IgG4 could separately develop from IgM-or other IgG isotypeexpressing cells. Such clonally related sequences were not iden- tified in our relatively large sequence collection (data not shown), indicating 1) that, within the overall repertoire, clonally related IgG4 and IgE transcripts may be less common than anticipated or 2) that the sample volume is too small to harbor a large collection of the available specificities.…”

Local Somatic Hypermutation and Class Switch Recombination in the Nasal Mucosa of Allergic Rhinitis Patients

“…PCR amplification of sequences from IgM ϩ , IgG ϩ , or IgA ϩ B cells was conducted as separate reactions based on a multiple step PCR published previously (28,29).…”