Haemophilus parainfluenzae antigen and antibody in children with IgA nephropathy and Henoch-Schönlein nephritis.

Although the pathogenesis of immunoglobulin A (IgA) nephropathy and Henoch-Schönlein nephritis (HSN) remains uncertain, there is substantial evidence that they are immune complex-mediated diseases. Recently, Haemophilus parainfluenzae antigens were shown in the glomerular mesangium of adult patients with IgA nephropathy, and greater levels of IgA antibody against H parainfluenzae were also shown in the sera of adult patients with IgA nephropathy. The present study was performed to detect H parainfluenzae antigens and antibody against H parainfluenzae in children with IgA nephropathy and HSN. H parainfluenzae antigens in the mesangium were examined by indirect immunofluorescence, and antibody against H parainfluenzae was examined by enzyme-linked immunosorbent assay. Diffuse global staining of the mesangium with rabbit antisera against H parainfluenzae was shown in 10 of the 32 patients (31%) with IgA nephropathy and 12 of the 34 patients (35%) with HSN. Conversely, only 2 of the 47 patients (4%) with other renal diseases showed staining of glomeruli with rabbit antisera against H parainfluenzae (IgA nephropathy versus other renal diseases, P = 0.003; HSN versus other renal diseases, P = 0.0006). Patients with IgA nephropathy and those with HSN showed significantly greater levels of plasma IgA1 antibody against H parainfluenzae than patients with other renal diseases (IgA nephropathy versus other renal diseases, P = 0.008; HSN versus other renal diseases, P = 0.025). These findings suggest that H parainfluenzae has a role in the cause of these two conditions in a subset of patients.