A significant proportion of patients with idiopathic rhinitis have positive nasal challenges, the vast majority to house dust mite allergen. These findings add to the weight of evidence that suggests 'localized allergy' may exist in the absence of systemic atopic markers.

Idiopathic and allergic rhinitic mucosa show similarities in their inflammatory infiltrate suggesting that both groups share a highly localized Th2, IgE-mediated cellular immunopathology.

PAR is characterized by increased numbers of CD3+, CD25+ and CD45RA+ T lymphocytes compared with normal mucosa. Allergic and nonallergic rhinitis groups can be separated by significant differences in the number of epithelial antigen presenting cells (APCs) (HLA-DRalpha+) and sub-epithelial activated (CD25+) T cells. Moreover, IR patients do not significantly differ to their allergic counterparts with respect to total (CD3+) and naïve (CD45RA+) T cell numbers, or numbers of epithelial activated (CD25+) lymphocytes. IR subjects show significantly increased numbers of CD8+ lymphocytes compared with control mucosa and although our findings suggest that the initiating inflammatory events may differ, both rhinitis groups show a similarity in pathology involving mucosal mast cells with an association to infiltrating T cells.

The pathophysiology of idiopathic rhinitis is unknown although evidence is accumulating to suggest that, in a proportion of patients, it may be a more localized form of allergic rhinitis in the absence of other atopic symptoms and markers. Anti-IgE is thought to be a systemic marker of atopy. This study compared serum IgG autoanti-IgE levels in patients with idiopathic rhinitis, perennial allergic rhinitis and normal controls. Serum samples were obtained from 19 patients with idiopathic rhinitis, 17 patients with perennial allergic rhinitis and 10 normal non-rhinitic controls. The presence or absence of IgG1 and IgG4 anti-IgE antibodies was detected using enzyme-linked immunosorbent assays. Eighty-eight percent of the patients with perennial allergic rhinitis had raised levels of autoanti-IgE antibodies in their serum. None of the controls or patients with idiopathic rhinitis showed raised levels (P < 0.001). Although patients with idiopathic rhinitis may exhibit clinical and pathological features of allergy, they do not show raised levels of anti-IgE in their serum.

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