Deletion of the fcgamma receptor IIb in thymic stromal lymphopoietin transgenic mice aggravates membranoproliferative glomerulonephritis

Abstract

Engagement of immunoglobulin-binding receptors (FcgammaR) on leukocytes and other cell types is one means by which immunoglobulins and immune complexes activate effector cells. One of these FcgammaRs, FcgammaRIIb, is thought to contribute to protection from autoimmune disease by down-regulation of B-cell responsiveness and myeloid cell activation. We assessed the role of FcgammaRIIb in a mouse model of cryoglobulin-associated membranoproliferative glomerulonephritis induced by overexpression of thymic stromal lymphopoietin (TSLP). TSLP transgenic mice were crossbred with animals deficient for FcgammaRIIb on the same genetic background (C57BL/6). Renal pathology was assessed in female and male animals (wild-type, FcgammaRIIb-/-, TSLP transgenic, and combined TSLP transgenic/FcgammaRIIb-/- mice) after 50 and 120 days, respectively. FcgammaRIIb-/- mice had no significant renal pathology, whereas overexpression of TSLP induced a membranoproliferative glomerulonephritis, as previously established. TSLP transgenic FcgammaRIIb-/- mice appeared sick with increased mortality. Kidney function was significantly impaired in male mice corresponding to aggravated glomerular pathology with increases in glomerular matrix and cellularity. This resulted from both a large influx of infiltrating macrophages and increased cellular proliferation. These results emphasize the important role of FcgammaRIIb in regulating immune responses and suggest that modulation of Fcgamma receptor activation or expression may be a useful therapeutic approach for treating glomerular diseases.

Figure 1.

Glomerular architecture. The figure depicts representative glomeruli from animals of each experimental group in a PAM stain. A and B: Normal glomerular architecture of wild-type and FcγIIbR−/− mice, respectively. C: A glomerulus from a TSLP transgenic mouse with increase in glomerular matrix. The glomerulus in D is from a TSLP transgenic animal with a deletion in the FcγIIb receptor and shows a significant increase in glomerular extracellular matrix and cellularity. Original magnifications, ×400.

Figure 2.

Glomerular α-smooth muscle actin expression. A: Semiquantitative assessment of glomerular α-smooth muscle actin expression. Graphs show mean ± SEM. Statistically significant differences between experimental groups are expressed as **, P < 0.01 and ***, P < 0.001. B: Immunohistochemical stain for α-smooth muscle actin; representative picture of glomerular α-smooth muscle actin expression in a wild-type mouse. C: Representative picture of glomerular α-smooth muscle actin expression in a TSLP transgenic FcγIIbR−/− animal. Original magnification, ×400 (B).

Figure 3.

Glomerular macrophages. Immunohistochemical stain for macrophages using a Mac-2 antibody. Glomeruli for wild-type (A) or FcγIIbR−/− (B) mice show occasional infiltration with macrophages (dark stain). In contrast, there is marked glomerular macrophage influx in TSLP transgenic animals as shown in C. FcγIIbR-deficient TSLP transgenic mice show a significant increase in macrophage influx compared to TSLP transgenic mice with functional FcγIIb receptor (D). Original magnification, ×400 (A).

Figure 4.

Glomerular deposition of immunoglobulins and complement. Graphs show semiquantitative assessment of glomerular immunoglobulin deposition and deposition of complement factor C3. Columns show mean ± SEM. Statistically significant differences between experimental groups are expressed as *, P < 0.05; **, P < 0.01; and ***, P < 0.001.