Synthesis of immunoglobulins against Haemophilus parainfluenzae by tonsillar lymphocytes from patients with IgA nephropathy

Background. We previously demonstrated glomerular deposition of Haemophilus parainfluenzae (HP) antigens and the presence of IgA antibody against HP a ntigens in patients with IgA nephropathy (IgAN). In this report we examine the synthesis of immunoglobulins against HP antigens in tonsillar lymphocyt es from patients with IgAN. Methods. We used tonsillar lymphocytes isolated from the palatine tonsils o f 15 patients with IgAN and 16 patients with chronic tonsillitis but withou t renal disease. We examined lymphocyte proliferation and production of IgA , IgG, and IgM antibodies against HP antigens by measuring thymidine uptake and concentrations of these antibodies in culture supernatants after lymph ocyte incubation with HP antigens by ELISA. Results. Lymphocytes from patients with IgAN showed a significantly higher stimulation index (SI) on exposure to HP antigens (thymidine incorporation in tonsillar lymphocytes exposed to HP (c.p.m.)/thymidine incorporation in unstimulated tonsillar lymphocytes (c.p.m.)) than did controls (P=0.0015). Lymphocytes from patients with IgAN also showed a significantly higher IgA SI (concentrations of IgA against HP antigens in supernatants from HP-stimu lated lymphocytes/IgA against HP antigens in supernatants from unstimulated tonsillar lymphocytes) than did controls (P=0.0004). We found positive cor relations between concentrations of IgA and IgG antibodies, between IgA and IgM antibodies, and between IgG and IgM antibodies against HP antigens aft er HP stimulation. Conclusions. Our results suggest that HP antigens stimulate tonsillar T and B lymphocytes in patients with IgAN and that these patients have polyclona l activation of lymphocytes against HP antigens, with isotype switching of antibody production from IgM to IgA.