Animal Models in Autoimmunity: Mouse Models in Rheumatology

Why Mouse Models?

• Understanding genetic susceptibility loci and specific pathogenic pathways
• Identifying novel autoantigens and immune mechanisms
• Preclinical testing of targeted therapies
• Dissecting gene-environment interactions

Criteria for Evaluating an Animal Model

Classification of Murine Autoimmune Models

I. Spontaneous Mouse Models

1. New Zealand Black (NZB) Mouse

• Early mortality (~16-17 months) due to hemolytic anemia (linked to Aia3 and Nba2 loci)
• B-cell hyperreactivity: hypergammaglobulinemia
• Mild immune complex glomerulonephritis
• Late-life B-cell lymphomas (similar to Sjögren's-associated lymphomas)
• Female mice slightly more affected than males (unlike the strong sex bias in humans)

2. (NZB × NZW)F1 (NZB/W, "BWF1") Mouse - The Classic SLE Model

• High-titer anti-dsDNA antibodies (a hallmark of SLE)
• Aggressive proliferative glomerulonephritis with tubulointerstitial disease - the major cause of early mortality
• Classic LE cells
• Lymphocytic infiltration of salivary glands (model for Sjögren's overlap)
• CNS abnormalities in common with SLE
• Strong female predominance - autoantibodies and renal disease appear earlier in females, mirroring human SLE

3. MRL/lpr and gld Mice

• The lpr mutation = a defect in Fas protein (CD95), a TNF-superfamily receptor critical for activation-induced cell death
• Results in massive, non-malignant lymphoproliferation and loss of peripheral tolerance
• Accumulation of "double-negative" (DN) T cells (CD4-CD8-) in the periphery - due to failure of programmed cell death, not abnormal proliferation
• Severe multi-organ autoimmunity: glomerulonephritis with complement deposition, necrotizing vasculitis (renal, mesenteric, coronary arteries), interstitial pneumonitis, skin disease, CNS inflammation
• Broad autoantibody production including anti-dsDNA, anti-Sm, anti-ribonuclear proteins (more comprehensive than NZB/W)
• Widely used for therapeutic testing in SLE

4. BXSB Mouse

• Y-linked disease accelerator gene called Yaa (Y-linked autoimmunity accelerator)
• Yaa acts as an accelerating factor but requires additional background genes for full disease
• This model was instrumental in demonstrating that Y-linked (non-hormonal) genetic factors can drive male-predominant autoimmunity
• Disease is worsened by IL-6

5. NZM2410 and Congenic Strains

• Sle1 (chromosome 1): B-cell hyperactivity, anti-dsDNA production; contains the SLAM/CD2 gene cluster (Sle1b) and C2 gene (Sle1c)
• Sle2 (chromosome 4): B-cell polyclonal activation
• Sle3/5 (chromosome 7): T-cell hyperactivation, increased APC activity

6. SNF1 Mouse (SWR × NZB)F1

• Mapping of autoepitopes on core histones for pathogenic T-cell clones
• Demonstrated the role of nucleosomes as autoantigens - histone H1'22-42 reactive Th1 cells expand early and accelerate glomerulonephritis

II. Induced Mouse Models

7. Collagen-Induced Arthritis (CIA) - The Gold Standard RA Model

Animals are immunized with type II collagen; an autoimmune response results when specific epitopes are presented in the context of MHC class II antigens and recognized by autoreactive CD4+ T-cell populations. Autoantibodies and T effector cells reactive against cartilage components develop and localize in synovial joints, causing immune-mediated inflammatory response. The immune response is perpetuated by release of cartilage antigens within the damaged joint, and chronic arthritis develops.

• CIA susceptibility is linked to the I-A region of the H-2d and H-2q haplotypes - a four-amino-acid sequence in the I-Aβ chain analogous to the human RA "shared epitope" in DRβ1
• CIA can now be induced in C57BL/6 (H-2b) background via the congenic C57BL/6N.Q strain, enabling use of gene knockout mice
• Both humoral (anti-CII antibodies) and cellular (CD4+ T cells) immunity are required
• Proinflammatory cytokines TNF-α and IL-1β are expressed in affected joints; blocking these reduces clinical and histological severity - directly predicting the success of anti-TNF therapy in humans
• Limitations: more acute than human RA; cyclooxygenase inhibitors are highly effective in CIA but less so in RA; most RA patients do NOT have elevated anti-CII antibodies

8. Proteoglycan/Aggrecan-Induced Arthritis (PGIA)

• Induced in BALB/c mice by immunization with the G1 domain of human aggrecan (proteoglycan)
• Histopathology: edema, proliferative synovitis, mononuclear infiltration, pannus formation, cartilage and bone erosion
• Both immune complex (IC) and T-cell dependent
• Provides a model for joint-specific autoimmunity to a cartilage-specific proteoglycan

9. Pristane-Induced Arthritis (PIA)

• Mechanism: Circulating macrophages are intensely activated by non-degradable oil components, producing high levels of IL-1, IL-6, TNF-α, and IFN-α. Genetic regulation governs the presence of autoreactive T and B cells, which become activated and clonally expand. Joint-reactive lymphocytes migrate to joints and induce damage. The release of cartilage antigens and heat shock proteins feeds back to autoreactive lymphocytes, creating chronic stimulation.

10. Antigen-Induced Arthritis (AIA)

• Induced in rabbits and mice by intraarticular injection of antigen (ovalbumin, BSA, methylated BSA) following systemic preimmunization with antigen in CFA
• Confined to the injected joint - unlike polyarthritis models
• Cationic antigens preferred due to increased retention in joint
• Both IC and T-cell dependent; T-cell-derived IL-17 drives the flare response
• Useful for studying monoarthritis mechanisms

11. Bleomycin-Induced SSc Model

• Repeated subcutaneous injections of bleomycin (or intradermal) induce skin fibrosis and pulmonary fibrosis mimicking systemic sclerosis
• A 2024 systematic review (Gülle et al., PMID: 38523580) comprehensively evaluates this model
• Main limitation: lack of autoantibody production typical of human SSc

III. Transgenic and Knockout (Engineered) Mouse Models

12. K/BxN Mouse - Spontaneous Autoimmune Arthritis

• Develops acute severe inflammatory arthritis driven by anti-GPI (glucose-6-phosphate isomerase) antibodies
• B lymphocytes, MHC class II, and CD4+ T cells are all required
• Arthritis can be transferred to naive mice with serum IgG (complement- and FcγR-dependent) - the K/BxN serum transfer model is widely used as a rapid, synchronous arthritis model
• Key limitation: unlike human RA, K/BxN arthritis is NOT TNF-α dependent; also, anti-GPI antibodies are not specific to RA in humans

13. SKG Mouse - ZAP-70 Mutant Arthritis

• Carries a spontaneous point mutation in the SH2 domain of ZAP-70 (a key TCR signaling kinase)
• Suboptimal TCR signal transduction alters the thymic selection threshold, failing to delete self-reactive T cells
• Develops chronic autoimmune arthritis reminiscent of RA, including synovitis, pannus, and cartilage destruction
• Challenges the assumption that autoimmune diseases arise from hyperresponsive T cells - here it is hypo-responsive TCR signaling
• Requires innate immune stimulation to trigger disease (microbially rich environment or fungal β-glucans such as zymosan), demonstrating gene-environment interaction
• Also develops extra-articular features (interstitial pneumonitis, Sjögren's-like features)

14. TNF Transgenic (TNFtg) Mouse

• Overexpression of human TNF in mice leads to spontaneous destructive arthritis
• Directly validated TNF as a driver of synovitis - helped establish the rationale for anti-TNF therapy
• Arthritis is T-cell and immune complex independent (pure cytokine-driven)

15. IL-1ra Knockout (IL-1ra-/-) Mouse

• BALB/c mice with targeted deletion of IL-1 receptor antagonist develop spontaneous arthritis
• Autoimmune T cells involved (±IC)
• Demonstrates the critical role of the IL-1 pathway in joint homeostasis

16. Engineered Lupus Models

IV. Mouse Models of Sjögren's Syndrome

V. Mouse Models of Systemic Sclerosis (SSc)

VI. Models for Vasculitis and Antiphospholipid Syndrome

Key Lessons from Mouse Models

1. Genetic complexity of autoimmunity: Multiple loci contribute and interact (NZM2410 studies)
2. Loss of negative regulation (Lyn, CD45 wedge mutant, FcRIIB, PD-1, CTLA4) consistently produces autoimmunity - tolerance requires active suppression
3. Both T and B cells are typically required for full autoimmune disease expression
4. Gene-environment interaction: SKG mice require fungal triggers; pristane-induced models show how environmental adjuvants engage autoreactive lymphocytes
5. Cytokine validation: TNF transgenic mice validated anti-TNF therapy; BAFF transgenic mice validated belimumab
6. Translation limitations: K/BxN arthritis is TNF-independent; CIA responds better to COX inhibitors than human RA; murine lupus drug studies frequently fail to translate to humans - due to differences in immune effector mechanisms

Recent Literature (PubMed)

• Systemic Sclerosis mouse models (Bi X, Mills T, Wu M, Curr Opin Rheumatol 2023 [PMID: 37605874]): Update on SSc animal models
• Bleomycin-induced SSc (Gülle S et al., Reumatismo 2024 [PMID: 38523580]): Systematic review of skin and lung fibrosis in bleomycin mouse models
• Immunometabolism in SLE (Patiño-Martinez E, Kaplan MJ, Nat Rev Rheumatol 2025 [PMID: 40524030]): NZM congenic strains now used to link immunometabolism to lupus pathogenesis