Distinct contribution of IL-6, TNF-alpha, IL-1, and IL-10 to T cell-mediated spontaneous autoimmune arthritis in mice

Abstract

Cytokines play key roles in spontaneous CD4(+) T cell-mediated chronic autoimmune arthritis in SKG mice, a new model of rheumatoid arthritis. Genetic deficiency in IL-6 completely suppressed the development of arthritis in SKG mice, irrespective of the persistence of circulating rheumatoid factor. Either IL-1 or TNF-alpha deficiency retarded the onset of arthritis and substantially reduced its incidence and severity. IL-10 deficiency, on the other hand, exacerbated disease, whereas IL-4 or IFN-gamma deficiency did not alter the disease course. Synovial fluid of arthritic SKG mice contained high amounts of IL-6, TNF-alpha, and IL-1, in accord with active transcription of these cytokine genes in the afflicted joints. Notably, immunohistochemistry revealed that distinct subsets of synovial cells produced different cytokines in the inflamed synovium: the superficial synovial lining cells mainly produced IL-1 and TNF-alpha, whereas scattered subsynovial cells produced IL-6. Thus, IL-6, IL-1, TNF-alpha, and IL-10 play distinct roles in the development of SKG arthritis; arthritogenic CD4(+) T cells are not required to skew to either Th1 or Th2; and the appearance of rheumatoid factor is independent of joint inflammation. The results also indicate that targeting not only each cytokine but also each cell population secreting distinct cytokines could be an effective treatment of rheumatoid arthritis.

Figure 1

Immunohistology of synovitis. Serial sections of a finger joint of a 5-month-old SKG mouse were stained for CD4 (A), CD8 (B), B220 (C), Gr-1 (D), CD11b (E), I-A/I-E (F), CD49d (G), or VCAM-1 (H) with staining control (I). Arrow indicates vasculature. Original magnification, ×20.

Figure 2

Expression of cytokines at mRNA and protein levels. (A) Quantitative RT-PCR for indicated genes was performed with ankle joints from 8- or 24-week-old SKG or BALB/c mice. Bars show the means ± SD. See Methods for the definition of units. (B) Concentrations of indicated cytokines, assessed by ELISA, in the joint fluid of 32-week-old SKG and BALB/c mice (n = 10 each). Bars show the means ± SD. (C–F) Immunohistochemical staining of the synovial tissue of a finger joint of a 4-month-old SKG mouse for IL-1β (C), TNF-α (D), or IL-6 (E), with staining control (F) (original magnification, ×40). Insets show higher magnifications of a part of synovium.

Figure 3

Development of arthritis in cytokine-deficient SKG mice. (A) Incidence and severity of arthritis in female SKG mice homozygously (–/–) (filled circles) or heterozygously (+/–) (open squares) deficient in indicated cytokines or cytokine-intact (+/+) (open triangles). Vertical bars represent the means ± SD of the whole group of mice. Arthritis scores are significantly different (P < 0.01) between IL-6^+/+ and IL-6^+/– mice at 19–32 weeks; between IL-6^+/– and IL-6^–/– mice at 16–32 weeks; between IL-1^+/+ and IL-1^+/– mice at 17–32 weeks; between IL-1^–/– and IL-1^+/– mice at 19–32 weeks; between TNF-α^+/+ and TNF-α^+/– mice at 15–32 weeks; between TNF-α^–/– and TNF-α^+/– mice at 21–32 weeks; between IL-10^+/+ and IL-10^+/– mice at 18–24 weeks; and between IL-10^–/– and IL-10^+/– mice at 12–24 weeks. (B–D) Histology of finger joints of a 32-week-old wild-type (B) or IL-6–deficient (C) or a 24-week-old IL-10–deficient SKG mouse (D) (original magnification, ×10).

Figure 4

Autoantibodies in cytokine-deficient SKG mice. RF (A) or anti–type II collagen (anti-CII) autoantibody titers (B) in 32-week-old SKG mice homozygously or heterozygously deficient in indicated cytokines, with wild-type SKG mice and age-matched BALB/c mice as controls. Filled circles indicate mice with joint swelling (arthritis score ≥ 1.0); open circles indicate mice without joint swelling (arthritis score < 1.0). First 10 mice that had reached 32 weeks of age in each group shown in Figure 3 were analyzed.