The clinical condition of IgA-deficient patients is related to the proportion of IgD- and IgM-producing cells in their nasal mucosa.

Nasal biopsy specimens from 15 adult patients with selective IgA deficiency but normal IgG-subclass levels were examined by immunohistochemistry for the presence of immunocytes producing various Ig isotypes. The mucosal samples were completely IgA-deficient except in two cases where 0.9% and 8.4% IgA cells were found, respectively (normal, 69.8%). Numerous IgG- (mainly IgG1-) producing cells were present in 10 samples; in five of these there were additional IgM- but virtually no IgD-producing cells, whereas in the other five a marked dominance of the IgD over the IgM isotype was seen. The latter category of patients had more upper airways infections (recurrent acute rhinosinusitis, otitis media, and tonsillitis) than the former, who had no recurrent upper respiratory tract infections except one patient with recurrent acute rhinosinusitis. The five remaining samples, which contained very few Ig-producing cells, were derived from patients with even more frequent infections than those showing IgD predominance. Our results indicate that IgM acts as a compensatory secretory Ig in the upper respiratory tract of some IgA-deficient subjects. However, immunoregulatory events favouring local IgD responses apparently do not support mucosal defence satisfactorily, either because local production of IgM is hampered or because IgD (which is not a secretory Ig) blocks complement-dependent reactions mediated by IgG and IgM antibodies within the mucosa.