Supernatants from peripheral blood mononuclear cells cultures of 30 id
iopathic, minimal lesion, nephrotic syndrome (IMLNS) patients in relap
se and the same patients in remission were fractionated by gel filtrat
ion chromatography. Fractions eluting with carbonic anhydrase (29 kilo
daltons) were infused for 5 days at the rate of 10 mu l/h into the lef
t renal artery of Wistar rats using an Alter osmotic pump. On the last
day of infusion, rats were injected with (35)sulfate (1.0 mCi/200 g)
intraperitoneally and killed after 8 h. Glomeruli were isolated and gl
omerular basement membrane (GEM) obtained. There was a significant inc
rease in (35)sulfate uptake by GEM of the infused kidney (302 +/- 92 c
pm/mg dry glomerular weight, mean +/- SEM) compared with the uptake se
en in the contralateral kidney (157 +/- 36, P < 0.01) when the fractio
n from IMLNS patients in relapse was infused. No significant differenc
es in (35)sulfate incorporation were seen between infused kidney (166
+/- 41) and contralateral kidney (172 +/- 64) when the same fraction f
rom patients in remission was administered. A significant increase in
albuminuria was seen on the last day of infusion (14.2 +/- 1.0 mg/24 h
, mean +/- SEM) when supernatant factor from IMLNS patients in relapse
was used. No significant differences in urinary albumin excretion pri
or to and after infusion were seen when the same fraction from IMLNS p
atients in remission was administered. The in vivo infusion of superna
tant factor from IMLNS patients in relapse increased the (35)sulfate u
ptake by GEM and augmented albuminuria, suggesting that the factor may
have pathogenic significance in the proteinuria of IMLNS.