Development of IgA nephropathy-like glomerulonephritis associated with Wiskott-Aldrich syndrome protein deficiency

Abstract

Wiskott-Aldrich syndrome (WAS) is a rare X-linked disorder caused by mutations in the WAS gene. Glomerulonephritis is a frequent complication, however, histopathological data from affected patients is scarce because the thrombocytopenia that affects most patients is a contraindication to renal biopsies. We found that WASp-deficient mice develop proliferative glomerulonephritis reminiscent of human IgA nephropathy (IgAN). We examined whether increased aberrant IgA production is associated with the development of glomerulonephritis in WASp-deficient mice. Serum IgA and IgA production by splenic B cells was increased in WASp-deficient mice compared to wild-type (WT) mice. A lectin-binding study revealed a reduced ratio of sialylated and galactosylated IgA in the sera from old WASp-deficient mice. Circulating IgA-containing immune complexes showed significantly higher titers in WASp-deficient mice compared to WT mice. These results indicate that the increased IgA production and aberrant glycosylation of IgA may be critically involved in the pathogenesis of glomerulonephritis in WAS.

Figure 1. Immune complex deposition and mesangial cell proliferation in WASp deficient mice

Biopsy specimens from WT controls and Was-KO mice were examined pathologically at different time points. PAS staining of A: WT (>12months) and B: Was-KO (<6months), C: Was-KO (6–12months), D: Was-KO (>12months). Immunofluorescence studies showed immune complex deposition in Was-KO mice. E: IgG, F: IgA, G: IgM, H: C3. Electron microscopic examinations showed mesangial and paramesangial deposits (I), and hump-like deposits (K) in Was-KO mice and no deposits in WT mice (J).

Figure 2. Development of proliferative glomerulonephritis increasing in severity with age

The degree of renal injuries was evaluated with PAS staining and scored (A). The columns represent the mean and bars show SD of samples for each age. Urinary albumin/creatinine ratio was determined in WT and Was-KO mice at different time points (B). The bars represent the mean ± SD of samples for each age.

Figure 3. Increased serum IgA, IgA production by splenic B cells and circulating IgA containing immune complexes in WASp-deficient mice

A: Serum IgA; serum IgA was determined by mouse IgA ELISA quantitation kit. Data were compared between WT control and Was-KO mice at different age groups. B: In vitro IgA production; splenic B cells were isolated by immunomagnetic isolation kit and the cells were cultured in vitro in the presence of LPS and various cytokines. After 4 d, supernatant samples were harvested and IgA levels determined. Data were compared between WT control and Was-KO mice. Circulating IgA containing immune complexes were also determined by ELISA. Data were compared between WT and Was-KO mice and expressed as OD′ at 405 nm. C: Serum circulating IgA-containing immune complex (IgA–C3) D: Serum circulating IgA-containing immune complex (IgA–IgG)

Figure 4. Lectin-binding IgA in sera

Lectin-binding IgA levels were determined by the specific lectin-binding assays as described in Methods. Data were compared between WT control and Was-KO mice at different time points. The data are shown as the ratios of specific lectin-binding IgA to total IgA for SNA (A) and RCA-I (B).