RESUMEN
BACKGROUND: IgE antibody-producing B cells are enriched in the nasal mucosa in patients with allergic rhinitis because of local class switching to IgE. The expressed IgE VH genes also undergo somatic hypermutation in situ to generate clonal families. The antigenic driving force behind these events is unknown. OBJECTIVE: To examine the possible involvement of a superantigen in allergic rhinitis, we compared the variable (VH) gene use and patterns of somatic mutation in the expressed IgE heavy-chain genes in nasal biopsy specimens and blood from allergic patients and the IgA VH use in the same biopsy specimens and also those from nonallergic controls. METHODS: We extracted mRNA from the nasal biopsy specimens of 13 patients and 4 nonallergic control subjects and PBMCs from 7 allergic patients. IgE and IgA VH regions were RT-PCR amplified, and the DNA sequences were compared with those of control subjects. We constructed a molecular model of VH5 to locate amino acids of interest. RESULTS: We observed a significantly increased frequency of IgE and IgA VH5 transcripts in the nasal mucosa of the allergic patients compared with the normal PBMC repertoire. Within IgE and IgA VH5 sequences in the nasal mucosa, the distribution of replacement amino acids was skewed toward the immunoglobulin framework regions. Three of 4 nonintrinsic hotspots of mutation identified in the VH5 sequences were in framework region 1. The hotspots and a conserved VH5-specific framework residue form a tight cluster on the surface of VH5. CONCLUSION: Our results provide evidence for the activity of a superantigen in the nasal mucosa in patients with allergic rhinitis.
Asunto(s)
Linfocitos B/inmunología , Inmunoglobulina E/genética , Cadenas Pesadas de Inmunoglobulina/genética , Región Variable de Inmunoglobulina/genética , Mucosa Nasal/inmunología , Rinitis Alérgica Perenne/inmunología , Rinitis Alérgica Estacional/inmunología , Adolescente , Adulto , Femenino , Humanos , Inmunoglobulina A/genética , Inmunoglobulina E/química , Cadenas Pesadas de Inmunoglobulina/química , Región Variable de Inmunoglobulina/química , Masculino , Persona de Mediana Edad , MutaciónRESUMEN
IgE-expressing B cells are over 1000 times more frequent in the nasal B cell than the peripheral blood B cell population. We have investigated the provenance of these B cells in the nasal mucosa in allergic rhinitis. It is generally accepted that expression of activation-induced cytidine deaminase and class switch recombination (CSR) occur in lymphoid tissue, implying that IgE-committed B cells must migrate through the circulation to the nasal mucosa. Our detection of mRNA for activation-induced cytidine, multiple germline gene transcripts, and epsilon circle transcripts in the nasal mucosa of allergic, in contrast to nonallergic control subjects, however, indicates that local CSR occurs in allergic rhinitis. The germline gene transcripts and epsilon circle transcripts in grass pollen-allergic subjects are up-regulated during the season and also when biopsies from allergic subjects are incubated with the allergen ex vivo. These results demonstrate that allergen stimulates local CSR to IgE, revealing a potential target for topical therapies in allergic rhinitis.