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In the renal biopsy samples of some patients with IgA glomerulonephritis (IgA GN), tubulointerstitial changes and a significant correlation between these changes and the serum creatinine levels had been observed earlier. In order to get an insight into the function of the tubules, 45 patients with IgA GN have been examined for proteinuria with special reference to low molecular weight (LMW) proteins, also called tubular proteins using sodium-dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE). Thirty-seven of the 45 patients had proteinuria (200-1890 mg/day). On the basis of the middle molecular weight/high molecular weight (MMW/HMW) protein ratio, the proteinuria was non-selective in 28. Twenty-nine patients had 40-200 mg LMW protein/day in the urine. There was a statistically significant correlation between the tubulointerstitial changes seen in the renal biopsy samples (characterized by the tubulointerstitial index) and the tubular proteinuria. On the basis of these results it is suggested that in most patients with IgA GN there is, in addition to the glomerular lesion, also morphological and functional tubulointerstitial damage, which is in connection with the progression of the disease.

Sera and plasmas from 50 patients with IgA nephropathy (IgA-NP) have been investigated for the presence of cryoglobulin (CG) and cryofibrinogen (CF), respectively, 2-5 cryoprotein determinations being made for each patient. CG was transiently found in 20 of 50 patients (40%), but in none of 20 healthy blood donors, whereas CF was found in 37 of 50 patients (74%) and in 4 of 20 healthy blood donors. The cryoprecipitates were of single and mixed component types. All but 2 of the patients with CF had haematuria. Nearly all of them had histories of long exposure to the cold as manual workers at the onset or recognition of their disease. There was no clinical remission during a 2-to-5-year follow-up if cryoproteinaemia persisted. A certain correlation was detected between the composition of the CP and the renal immunohistological findings. It is suggested that renal deposition of circulating CF or local formation of CF might be responsible for the tubulo-interstitial fibrocellular changes, which are of prognostic importance.

It might be supposed that, among the antigens causing chronic immune complex glomerulonephritis (IC GN), there are foreign materials, e.g. bacterial antigens penetrating the mucosal barrier. To put this hypothesis to the test, the presence and titres of IgA and IgG antibodies against Chlamydia (C., one of the most frequent bacteria causing mucosal inflammation) have been studied in the sera of 70 patients with IgA nephropathy (IgA NP), of 25 with mesangiocapillary GN (MCGN) and of 27 with membranous GN (MGN) using a single serovar (L2) inclusion immunoperoxidase assay. Significantly more IgA (titres greater than or equal to 8) and IgG (titres greater than or equal to 32) antibodies were found in the sera of IgA NP and MCGN patients than in healthy controls. These results are compatible with the hypothesis that there are some similarities between the clinical and morphological picture of IgA NP and MCGN. Furthermore, it may be assumed that in renal patients with an active C. infection (high IgG titres with IgA seropositivity) C. antigens may play a role in the production of nephropathogenic IC developing in antibody excess.

Renal biopsy material of 50 patients suffering from IgA glomerulonephritis was studied by light microscopy, immunofluorescence and occasionally electron microscopy. Associated with a uniform immunohistological pattern mainly focal or diffuse mesangial proliferative glomerulonephritis was found. In addition to the glomerular changes the importance of frequent extraglomerular, mainly vascular and interstitial, alterations is stressed. In arterioles and arteries, deposition of a hyalinous substance was observed. Immunohistology revealed the presence of immunoglobulins and/or C3 in the vessels. In the interstitium fibrinogen/fibrin was often seen, accompanied by chronic inflammatory infiltration and fibrosis.

The authors investigated the tubulointerstitial changes (atrophic tubuli, interstitial fibrosis and round-cell infiltration) by two methods in renal biopsies from 56 patients with IgA glomerulonephritis. A statistically significant correlation was found to exist between the tubulointerstitial changes and serum creatinine level at the time of renal biopsy. A statistical significant correlation was also established between serum creatinine at the end of a period of 5 years of follow-up and tubulointerstitial changes. Their results suggest that severe tubulointerstitial lesions in IgA glomerulonephritis carry a poor prognosis.