Enhanced expression of the CD71 mesangial IgA1 receptor in Berger disease and Henoch-Schönlein nephritis: association between CD71 expression and IgA deposits.

ABSTRACT. IgA nephropathy (IgA-N) that comprises Berger disease and Henoch-Schönlein Purpura (HSP) nephritis is defined by mesangial IgA deposits. Recently, this group has characterized a new receptor for IgA, the transferrin receptor (CD71), expressed on mesangial cells. To assess whether CD71 was involved in the pathogenesis of IgA-N, its expression was analyzed together with IgA deposits on 16 kidney biopsies from 16 patients with Berger disease (n = 4) or HSP (n = 12). These biopsies were compared with 17 kidney biopsies of a group of 15 patients (control group) with other glomerulonephritis, including systemic lupus erythematosus, poststreptococcal acute glomerulonephritis, membranoproliferative glomerulonephritis, steroid-sensitive minimal change nephrotic syndrome, steroid-resistant idiopathic nephrotic syndrome with focal and segmental glomerulosclerosis, and persistent and isolated proteinuria with minimal change on kidney biopsy. In this control group, IgA deposits could be observed in eight kidney biopsies of seven patients. These biopsies were also compared with normal kidney specimens (normal group). In normal kidney, it was found that CD71 was linearly expressed on tubular epithelium but was either not expressed or very dimly in glomeruli. In contrast, CD71 was strongly expressed in 105 of the 107 glomeruli of the kidney biopsies from the IgA-N group. For the control group, it was found that expression of CD71 in glomeruli was correlated to the presence of IgA deposits. Indeed, among the 87 glomeruli of nine kidney biopsies (eight patients) without IgA fixation, 78 exhibited no CD71 expression and nine exhibited a very dim one. On the other hand, all 49 glomeruli of the eight kidney biopsies (seven patients) in which IgA deposits were detected exhibited CD71 expression (P < 10(-4)). Performance of dual-labeling studies with confocal microscopy on kidney biopsies of IgA-N patients demonstrated that most of the IgA deposits co-localized with CD71. It was also demonstrated that the intensity of the expression of CD71 was not linked to the intensity of clinical or biologic findings but to the intensity of cellular proliferation in both IgA-N and control groups. These results show that mesangial CD71 expression is not specific to IgA-N. However, the association between IgA deposits and CD71 expression and their co-localization in the mesangium provide strong evidence that CD71 is a major IgA receptor on mesangial cells.