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Humoral immunological reactions play a central part in the development of nephropathies. Immune complexes may form in the circulation and precipitate in the kidney, or form in the kidney by binding of antibodies from the circulation to antigens in the glomerular basement membrane. The localizations of immune complex deposition in the various compartments of the glomeruli determine the development of different forms of glomerulonephritis. Cellular immunological reactions play a part in the development of tubulo-interstitial nephritis and possibly also of minimal change nephropathy' and focal segmental glomerulosclerosis. The role of cellular immunological reactions in the development of most other nephropathies is less clear. Persistence of nephropathies leads to glomerulosclerosis and renal interstitial fibrosis. Ultimately, these cause loss of kidney function and necessitate haemodialysis.

Objective: To determine the prevalence of complement system deficiencies in patients who have survived a Neisseria meningitidis infection., Design: Retrospective., Setting: Reference laboratory for bacterial meningitis of the University of Amsterdam and the National Institute of Public Health and Environmental Protection., Method: Out of the files of the laboratory 187 patients who had experienced a meningococcal infection in the Netherlands between 1959-1990 were selected in two groups according to the infecting bacterial strain: 97 patients with a serogroup X, Y, Z, W135, 29E, or non-groupable strains and 90 patients with an infection due to serogroup A or C. The patients were asked for their cooperation by their family doctor and one of us visited the patients at home to take blood samples. The complement activity was studied with a haemolysis in gel test and with an assay of haemolytic activity in free solution., Results: Complement deficiency was present in 18% of the 187 patients who had experienced a meningococcal infection. The highest prevalence was found in patients older than 10 years who had developed infections due to serogroups X, Y, W135, or non-groupable strains (45%). Of the patients with a serogroup A or C infection, 3% had an complement deficiency. Of the complement deficiencies, 42% concerned a component of the alternative pathway, 12% a deficiency of C3, and 46% a component of the terminal route. The most commonly found deficiencies were properdin deficiency (39%) and C8 deficiency (18%). 30% of the complement deficient patients reported other family members having experienced meningitis. Recurrent meningitis was only observed in patients with terminal route deficiencies., Conclusion: We recommend that patients with a meningococcal infection due to serogroups X, Y, W135 or non-groupable strains should be screened for complement deficiency.

The pathogenesis of IgA nephropathy has remained elusive in the twenty years that have passed since the first description of the disease. Based on the recent literature, we present a pathogenetic model in which a primary disorder of immune regulation plays a central role. This disorder of immune regulation results in an increased synthesis of plasma IgAI antibodies by the bone marrow, in response to everyday mucosal infections. Through an unknown mechanism, these circulating IgAI antibodies deposit in the mesangium, and cause an inflammatory response.