ROLE OF IGA, IGG, AND IGM ANTIBODIES AGAINST HAEMOPHILUS-PARAINFLUENZAE ANTIGENS IN IGA NEPHROPATHY

We have recently demonstrated glomerular deposition of outer membranes of Haemophilus parainfluenzae (HP) antigens (OMHP) and the presence o f IgA antibody against OMHP in patients with IgA nephropathy (IgA-N). In this study, we analyzed IgA-, IgG-, and IgM-classes of antibodies a gainst OMHP, and the relationship between these antibodies and renal l esions in IgA-N. The subjects included 44 patients with IgA-N and 62 p atients with other glomerular diseases (OGD); the latter group consist ed of 23 patients with predominantly IgG or IgM deposits and small amo unts of IgA in the mesangium (group A), and 39 with IgG or IgM deposit s without IgA (group B). IgA, IgG, and IgM antibodies against OMHP in patient sera were detected by enzyme-linked immunosorbent assay (ELISA ). Immunoblotting demonstrated that the IgA, IgG, and IgM antibodies a gainst OMHP in the sera of IgA-N patients bound to components of OMHP with molecular weights of 19.5, 30, and 40.5 kD. The amino acid compos itions of these three OMHP components were similar to those reported f or the outer membrane protein (OMP) P6 precursor, OMP P5, and OMP P2 ( porin) of Haemophilus influenzae. Both IgA-N and group A patients, (i. e. those with IgA-related renal disease), demonstrated a significantly higher level of IgA antibodies against OMHP than did group B patients . However, only IgA-N patients revealed a significant correlation betw een the IgA-antibody titer and degree of glomerular changes. IgA-N pat ients with macroscopic hematuria or arterio(lo)sclerosis had a signifi cantly higher IgA antibody titer than other IgA-N patients. There was no relationship between renal lesions and IgG or IgM antibody titers i n any group. These findings suggest that IgA antibodies against OMHP a re significantly increased in patients with IgA-related renal disease compared to those without mesangial IgA deposits and that a significan t relationship between these antibodies and renal lesions exists only in patients with IgA-N.