Local isotype switching of IgE within allergic nasal mucosa in response to allergen exposure

Patients with allergic rhinitis exhibit an exaggerated nasal response to allergen, in large part a consequence of IgE-mediated inflammatory cell activation. IgE within the tissue is considered to derive from IgE-bound inflammatory and/or IgE+ plasma cells. Resting B lymphocytes and cells expressing IL-4 and IL-13, cytokines that induce B cells to undergo epsilon germline transcription and isotype switching to IgE, are present within allergic nasal mucosa. As such, it has been hypothesized here that local isotype switching to IgE may occur at this site. Probes to detect the epsilon germline transcript (Iepsilon RNA), a pre-requisite for isotype switch recombination, the mature epsilon transcript (Cepsilon RNA) and IL-4 and IL-13 mRNA were employed. Since steroids reduce the number of cells expressing these cytokines, the effect of pre-treating patients with fluticasone propionate (FP) was also investigated.Nasal biopsies were obtained from seasonal allergic rhinitis patients before and following in vivo allergen challenge or natural exposure during the pollen season. To confirm local RNA synthesis, nasal tissue was challenged with allergen ex vivo. Immunocytochemistry (ICC) confirmed the presence of B cells within the nasal tissue. In situ hybidization (ISH) demonstrated increases in the number of Cepsilon and IL-4 mRNA and the appearance of Iepsilon RNA+ cells in nasal tissue from placebo-treated patients following in vivo allergen exposure, but not those pre-treated with FP. Ex vivo allergen challenge also resulted in higher numbers of Cepsilon, Iepsilon, IL-4 and IL-13 RNA+ cells in allergen-stimulated compared to unstimulated tissue. With simultaneous ICC/ISH, CD20+/Cepsilon+ (37%) and CD20+/Iepsilon+ (32%) were observed, while the presence of mature epsilon mRNA (Cepsilon+/Iepsilon-) was confirmed using double ISH. Furthermore, IL-4 was associated primarily with T cells (≅70%) and mast cells (≅32%), while these cell types also produced IL-13 (≅44%, ≅18%).It is demonstrated here that the epsilon germline transcript, mature epsilon mRNA and IL-4 and IL-13 mRNA are synthesized locally within allergic nasal mucosa and that steroids inhibit their production. These results indicate that events within the nasal mucosa itself play a primary role in regulating the allergic response at this site and emphasize the importance of focusing on this local regulation when designing future diagnostic and therapeutic strategies