Production of interferon-γ by tonsillar lymphocytes from patients with IgA nephropathy induced by stimulation with Haemophilus parainfluenzae antigens

IgA nephropathy (IgAN) is characterized by the presence of IgA deposits, predominantly in the glomerular mesangium, and by mesangial proliferative glomerulonephritis (GN). Concerning its pathogenesis, several investigators have suggested that the glomerular IgA deposits in IgAN are antibodies (Ab) to viral, bacterial or dietary antigens. Thus, the Ab are probably produced as part of the specific host immune response to various environmental antigens. Such reports strengthen the possibility of a relationship between mucosal immunity and the pathogenesis of IgAN. Nevertheless, attempts to isolate a specific IgA circulating immune complex-associated antigen in patients with IgAN have been unsuccessful. We have shown that mucosal infections such as pharyngitis are often associated with the acute onset of IgAN.1 IgAN is, then, an immune complex disease that is caused by a poor mucosal immune response to environmental antigens to which the patient has been chronically exposed. We have observed previously that Haemophilus parainfluenzae (HP) is more commonly isolated from the pharynx of patients with IgAN than from those with other glomerular diseases.2 We have also identified the glomerular deposition of outer membranes of HP antigens (OMHP) and an increased serum concentration of IgA-Ab against OMHP in patients with IgAN.2 Furthermore, we have shown that patients with IgAN have a specific increase in the production of IgA-Ab against OMHP via polyclonal activation against these, with switching of production from one isotype to another (e.g. from IgM to IgA3), and that a significant relationship between IgA-Ab against OMHP and renal lesions exists in patients with IgAN,4 and that OMHP stimulate tonsillar B-lymphocytes to produce specific IgA1-Ab against OMHP and tonsillar T-lymphocytes in patients with IgAN.5,6 Our objective was to investigate the production of IgA and several cytokines by tonsillar lymphocytes from patients with IgAN induced by stimulation with OMHP. We used tonsillar lymphocytes from the palatine tonsils of 18 patients with IgAN and 25 patients with chronic tonsillitis but without renal diseases as controls. There were no significant differences in the backgrounds of the two groups. Haemophilus parainfluenzae was detected in the tonsils of all 43 patients before tonsillectomy. We examined production of total IgA, IgA-Ab against OMHP, IL-4, IL-6, IL-10, and TGF-β in the culture supernatants after lymphocyte incubation with OMHP. The spontaneous production of total IgA and TGF-β by tonsillar lymphocytes from patients with IgAN was higher than that by tonsillar lymphocytes from controls (P < 0.05). Stimulation with OMHP in vitro enhanced the production of HP-specific IgA by tonsillar lymphocytes from patients with IgAN (P < 0.01), but not by tonsillar lymphocytes from controls. Outer membranes of HP stimulation also enhanced the production of TGF-β and IL-10 by tonsillar lymphocytes from patients with IgAN (P < 0.001). Our results suggest that the infection of HP in the tonsil may be involved in the aetiology of IgAN.