Immune response of tonsillar lymphocytes to Haemophilus parainfluenzae in patients with IgA nephropathy.

The pathogenesis of IgA nephropathy (IgAN) is unclear. We have previously shown glomerular deposition of Haemophilus parainfluenzae (HPI) antigens and the presence of IgA antibody against HPI antigens in patients with IgAN. We examined the immune response to HPI antigens in tonsillar lymphocytes from patients with IgAN. Lymphocytes isolated from the palatine tonsils of 13 IgAN patients and 16 patients with chronic tonsillitis but without renal disease were used as controls. We examined lymphocyte proliferation and production of IgA antibody against HPI antigens by measuring thymidine uptake and IgA antibody in culture supernatants after lymphocyte incubation with HPI antigens. Patients with IgAN showed a significantly higher stimulation index to HPI antigens (thymidine incorporation in tonsillar lymphocytes with HPI/thymidine incorporation in unstimulated tonsillar lymphocytes) than controls (P < 0.002). Lymphocytes from patients with IgAN also showed a significantly higher level of IgA antibody and IgA1 antibody against HPI antigens in culture supernatants than lymphocytes from controls (P = 0.0002 and P = 0.004, respectively). Our results suggest that HPI antigens stimulate tonsillar T and B lymphocytes in patients with IgAN and that an immune response to HPI antigens may play a role in the pathogenesis of this disease in some cases.