THE ROLE OF I AND B IN PERITONITIS ASSOCIATED WITH THE NEPHROTIC SYNDROME OF CHILDHOOD

Children with nephrotic syndrome (NS) are susceptible to bacterial inf ections, including primary bacterial peritonitis. Immunologic abnormal ities associated with NS include low serum levels of the complement pr oteins I and B of the alternative complement pathway. We developed a n ovel and highly sensitive enzyme immunoassay using murine MAb to I and B to quantitate urinary concentrations of these proteins. We studied 22 patients with minimal change NS, including seven with a history of peritonitis (1.6 +/- 0.3 episodes, mean +/- SEM) and 15 without such a history. The two groups did not differ significantly in age, sex, rac e, age at onset of disease, or duration of disease. Children with mini mal change NS complicated by peritonitis had 1) increased urinary excr etion of both I (p < 0.05) and B (p < 0.05) in relapse versus remissio n, 2) greater excretion of I in both relapse (p < 0.01) and remission (p < 0.05) compared with patients without peritonitis, 3) greater excr etion of B in relapse compared with patients without peritonitis (p < 0.05), and 4) decreased plasma levels of I compared with patients with out peritonitis and controls (p < 0.01) and decreased plasma levels of B compared with controls. Increased urinary excretion of I correlated with decreased plasma levels of I (r = 0.88, p < 0.001). These data s upport our initial hypothesis that depressed plasma concentrations of these proteins of the alternative complement pathway may predispose pa tients with minimal change NS to peritonitis and that urinary loss of these proteins is a tenable mechanism.