Focal and segmental glomerulosclerosis induced in mice lacking decay-accelerating factor in T cells

Abstract

Heritable and acquired diseases of podocytes can result in focal and segmental glomerulosclerosis (FSGS). We modeled FSGS by passively transferring mouse podocyte-specific sheep Abs into BALB/c mice. BALB/c mice deficient in the key complement regulator, decay-accelerating factor (DAF), but not WT or CD59-deficient BALB/c mice developed histological and ultrastructural features of FSGS, marked albuminuria, periglomerular monocytic and T cell inflammation, and enhanced T cell reactivity to sheep IgG. All of these findings, which are characteristic of FSGS, were substantially reduced by depleting CD4+ T cells from Daf(-/-) mice. Furthermore, WT kidneys transplanted into Daf(-/-) recipients and kidneys of DAF-sufficient but T cell-deficient Balb/(cnu/nu) mice reconstituted with Daf(-/-) T cells developed FSGS. In contrast, DAF-deficient kidneys in WT hosts and Balb/(cnu/nu) mice reconstituted with DAF-sufficient T cells did not develop FSGS. Thus, we have described what we believe to be a novel mouse model of FSGS attributable to DAF-deficient T cell immune responses. These findings add to growing evidence that complement-derived signals shape T cell responses, since T cells that recognize sheep Abs bound to podocytes can lead to cellular injury and development of FSGS.

Figure 1. Anti-podo Ab–induced FSGS in DAF-deficient animals.

(A) Significant albuminuria occurred in Daf^–/– and Cd59^–/–Daf^–/– mice 30 days after administration of anti-podo Abs. (B–D) Representative photomicrographs 30 days after anti-podo injection show glomerular localization of sheep and mouse IgG (B) and mouse C3 (C) in the 4 groups; (D) PAS-stained kidney sections show segmental sclerosis (arrows) only in Daf^–/– and Cd59^–/–Daf^–/– mice. (E) The extent of glomerulosclerosis in individual mice 30 days after administration of anti-podo Abs is shown. (F) Extensive podocyte foot process effacement and prominent remodeling of the external surface of the glomerular basement membrane (arrow) was seen by electron microscopy in DAF-deficient mice 30 days after anti-podo Abs administration. Asterisk denotes Bowman capsule. Numeric data shown in A and E from Daf^–/– and Daf^–/–Cd59^–/– mice were normally distributed, with means and 95% CIs shown as horizontal lines and open boxes, respectively. Data from WT and Cd59^–/– mice were nonparametric (Anderson-Darling test; P < 0.05); when sufficiently different from the origin, the 95% CI for the median is shown as an open box. Original magnification, ×400 (B–D); ×7,100 (F).

Figure 2. Immunological events induced by anti-podo Abs in DAF-deficient mice.

(A) In the kidneys of all mice, there was little neutrophil (brown) or B cell (purple) infiltration, while in DAF-deficient mice, there was marked infiltration with Thy-1.2⁺ T cells (brown) and F4/80⁺ monocytic cells (purple). Original magnification, ×400. (B) Flow cytometric analysis of cells isolated from kidneys of DAF-deficient mice 30 days after anti-podo Ab administration showing relative proportions of F4/80⁺ and CD3⁺ cells (left panel). The majority of F4/80⁺ cells were also CD11c⁺ (right panel). Numbers shown are the percentage of total cells in individual quadrants. (C) Splenic CD4⁺ cells from WT and DAF-deficient mice were assessed for CD62L (upper panels) and CD44 expression (lower panels) at baseline (d0) and 10 (d10) and 20 days (d20) after passive administration of anti-podo IgG. The CD62L^lo and CD44^hi populations are denoted by horizontal lines.

Figure 3. Kidney transplantation studies reveal extrarenal DAF deficiency is necessary for development of anti-podo Ab–induced FSGS.

(A) Representative glomerular histopathology 30 days after anti-podo Ab administration in native WT and transplanted Daf^–/– kidneys in a WT mouse and native Daf^–/– and transplanted WT kidneys in a Daf^–/– mouse. FSGS only developed in native and transplanted WT kidneys in Daf^–/– mice. Arrows depict regions of segmental sclerosis/hyalinosis. Original magnification, ×400. (B) Shown is the extent of glomerulosclerosis in individual kidneys within each group. Data from native and transplanted kidneys in Daf^–/– mice were normally distributed, while native and transplanted kidney data in WT mice were nonparametric (Anderson-Darling test; P < 0.05). Means and 95% CIs are shown as horizontal lines and open boxes, respectively.

Figure 4. Susceptibility to anti-podo Ab–induced FSGS occurs when DAF is absent from T cells.

(A) Shown are urinary albumin excretion (left) and the extent of glomerulosclerosis (right) 30 days after administration of anti-podo Abs in individual Daf^–/– mice depleted of CD4⁺ cells, with mAb GK1.5 or controls receiving irrelevant rat IgG_2b. All data were normally distributed (Anderson-Darling test; P > 0.05) and compared by t testing, with P values provided above the data. (B) Infiltration with Thy-1.2⁺ T cells (brown, arrow) and F4/80⁺ monocytic cells (purple, arrow) was significantly reduced 30 days after administration of anti-podo Abs in CD4⁺ cell–depleted but not control Daf^–/– mice. (C) Balb/c^nu/nu mice reconstituted with DAF-deficient but not WT T cells developed albuminuria and FSGS. Urinary albumin excretion (left) and the percentage of segmentally sclerotic glomeruli (right) in individual Balb/c^nu/nu mice that received T cells from WT (blue symbols) or Daf^–/– mice (red symbols) 30 days after administration of anti-podo Abs. Experiments differed by whether mice were reconstituted with partially (diamonds) or highly (circles) purified T cells. All data sets in mice receiving T cells from Daf^–/– mice were normally distributed with no differences comparing partially and highly purified T cells. Means and 95% CIs for the combined groups are shown as horizontal bars and open boxes, respectively. (D) Representative PAS-stained kidney sections from individual mice show the presence of segmental sclerosis (arrow) only in mice with DAF-deficient T cells. Original magnification, ×600.

Figure 5. Abnormal anti-sheep IgG responses occur when DAF is absent outside T cells.

(A) Serum mouse IgG, IgG₁, and IgG_2a anti-sheep IgG titers were higher in WT (open diamonds) and Cd59^–/– mice (filled squares) compared with Daf^–/– (filled circles) and Cd59^–/–Daf^–/– (X’s) mice. *P < 0.01, IgG concentration in DAF-sufficient versus DAF-deficient mice. (B) Balb/c^nu/nu mice reconstituted with T cells from Daf^–/– (filled diamonds) or WT mice (open squares) had comparable serum titers of mouse IgG, IgG₁, and IgG_2a anti-sheep IgG. Data shown represent mean ± SEM.