Human MHC Class II and Invariant Chain Knock-in Mice Mimic Rheumatoid Arthritis with Allele Restriction in Immune Response and Arthritis Association

Transgenic mice expressing human major histocompatibility complex class II (MHCII) risk alleles are widely used in autoimmune disease research, but limitations arise due to non-physiologic expression. To address this, physiologically relevant mouse models are established via knock-in technology to explore the role of MHCII in diseases like rheumatoid arthritis. The gene sequences encoding the ectodomains are replaced with the human DRB1*04:01 and 04:02 alleles, DRA, and CD74 (invariant chain) in C57BL/6N mice. The collagen type II (Col2a1) gene is modified to mimic human COL2. Importantly, DRB1*04:01 knock-in mice display physiologic expression of human MHCII also on thymic epithelial cells, in contrast to DRB1*04:01 transgenic mice. Humanization of the invariant chain enhances MHCII expression on thymic epithelial cells, increases mature B cell numbers in spleen, and improves antigen presentation. To validate its functionality, the collagen-induced arthritis (CIA) model is used, where DRB1*04:01 expression led to a higher susceptibility to arthritis, as compared with mice expressing DRB1*04:02. In addition, the humanized T cell epitope on COL2 allows autoreactive T cell-mediated arthritis development. In conclusion, the humanized knock-in mouse faithfully expresses MHCII, confirming the DRB1*04:01 alleles role in rheumatoid arthritis and being also useful for studying MHCII-associated diseases.

Fcgr2b and Fcgr3 are the major genetic factors for cartilage antibody-induced arthritis, overriding the effect of Hc encoding complement C5

Like rheumatoid arthritis (RA) in humans, collagen-induced arthritis (CIA) in mice is associated with not only MHC class II genetic polymorphism but also, to some extent, with other loci including genes encoding Fc gamma receptors (FCGRs) and complement C5. In this study, we used a cartilage antibody-induced arthritis (CAIA) model in which arthritis develops within a 12-h timeframe, to determine the relative importance of FCGRs and C5 (Hc). In CAIA, inhibiting or deleting FCGR3 substantially hindered arthritis development, underscoring the crucial role of this receptor. Blocking FCGR3 also reduced the levels of FCGR4, and vice versa. When employing an IgG1 arthritogenic cocktail that exclusively interacts with FCGR2B and FCGR3, joint inflammation was promptly initiated in Fcgr2b-- mice but not in Fcgr3-- mice, suggesting that FCGR3 is sufficient for CAIA development. Regarding complement activation, Fcgr2b++.Hc** mice with C5 mutated were fully resistant to CAIA, whereas Fcgr2b--.Hc** mice developed arthritis rapidly. We conclude that FCGR3 is essential and sufficient for CAIA development, particularly when induced by IgG1 antibodies. The human ortholog of mouse FCGR3, FCGR2A, may be associated with RA pathogenesis. FCGR2B deficiency allows for rapid arthritis progression and overrides the resistance conferred by C5 deficiency.

Antibodies against malondialdehyde among 60-year-olds: prediction of cardiovascular disease

Malondialdehyde (MDA) is generated in oxidized LDL. It forms covalent protein adducts, and is recognized by antibodies (anti-MDA). We previously studied IgM anti-MDA, and here we focus on IgG, IgG1 and IgG2 anti-MDA in predicting cardiovascular disease (CVD). We determined, by ELISA, anti-MDA in a 7-year follow-up of 60-year-old men and women from Stockholm County (2039 men, 2193 women). We identified 210 incident CVD cases (defined as new events of myocardial infarction (MI), and hospitalization for angina pectoris) and ischemic stroke, and 620 age- and sex-matched controls. IgG anti-MDA was not associated with CVD. Median values only differed significantly for IgG1 anti-MDA among men, with lower levels among cases than controls (p = 0.039). High IgG1 anti-MDA (above 75th percentile) was inversely associated with CVD risk after adjustment for smoking, body mass index, type 2 diabetes, hyperlipidemia, and hypertension, (OR and 95% CI: 0.59; 0.40-0.89). After stratification by sex, this association emerged in men (OR and 95% CI: 0.46; 0.27-0.77), but not in women. IgG2 anti-MDA were associated with protection in the whole group and among men though weaker than IgG1 anti-MDA. IgG2 anti-MDA above the 75th percentile was associated with an increased risk of MI/angina in women (OR and 95% CI: 2.57; (1.08-6.16)). IgG1 and less so IgG2 anti-MDA are protection markers for CVD and MI/angina in the whole group and among men. However, IgG2 anti-MDA was a risk marker for MI/angina among women. These findings could have implications for both prediction and therapy.

Mannan-induced Nos2 in macrophages enhances IL-17-driven psoriatic arthritis by innate lymphocytes

Previous identification of the inducible nitric oxide synthase (NOS2) gene as a risk allele for psoriasis (Ps) and psoriatic arthritis (PsA) suggests a possible pathogenic role of nitric oxide (NO). Using a mouse model of mannan-induced Ps and PsA (MIP), where macrophages play a regulatory role by releasing reactive oxygen species (ROS), we found that NO was detectable before disease onset in mice, independent of a functional nicotinamide adenine dinucleotide phosphate oxidase 2 complex. MIP was suppressed by either deletion of Nos2 or inhibition of NO synthases with NG-nitro-l-arginine methyl ester, demonstrating that Nos2-derived NO is pathogenic. NOS2 expression was also up-regulated in lipopolysaccharide- and interferon-γ-stimulated monocyte subsets from patients with PsA compared to healthy controls. Nos2-dependent interleukin-1α (IL-1α) release from skin macrophages was essential for arthritis development by promoting IL-17 production of innate lymphoid cells. We conclude that Nos2-derived NO by tissue macrophages promotes MIP, in contrast to the protective effect by ROS.