Immunologic hypersensitivity to collagen, the major structural component of connective tissue, could explain both the systemic nature and chronicity of the inflammation occurring in rheumatoid arthritis. Recent demonstrations of antibodies to collagen in sera from patients with rheumatoid arthritis support this premise (1-8). Also consistent with this hypothesis is the distribution of collagen in structurally distinct types in various tissues. For example, types I and HI collagens are found in the skin and parenchyma of several organs, whereas type II exists in cartilage (9). Thus, an immune response to the cartilage type of collagen (type II) could explain the predilection of rheumatoid arthritis to involve diarthrodial joints.Native collagens consist of three polypeptide chains linked in triple helices. Terminal peptides (telopeptides) do not have a helical structure and are more variable in amino acid content (10). Type I collagen combines two al-type I chains with one a2-chain and is depicted as [al(I)]2a2. Types II and III collagens are comprised of three al-type II chains and three al-type HI chains, respectively. Thus, type II is depicted as [al(II)]3 and type III as [al(III)]3.Injection of heterologous type I and II collagen in complete Freund's adjuvant has been reported to elicit type-specific antibody responses in rats (11) and mice (12). This paper reports that approximately 40% of rats injected intradermally with native type H collagen, derived from human, chick, or rat cartilage, in either complete or incomplete Freund's adjuvant, develop an inflammatory arthritis. In contrast, type I and III collagen are not arthritogenic. This new animal model suggests that immune responses to type II collagen could play a role in inciting or perpetuating joint inflammation in other arthritides. Materials and MethodsRats. Outbred female Wistar, Sprague-Dawley and inbred Wistar-Lewis rats were obtained from Microbiological Associates (Bethesda, Md.), Harlan (Indianapolis, Ind.) or Charles River Breeding Laboratory (Wilmington, Mass.). These rats were housed in metal cages and given water

Analysis of the IgG autoantibody subclass response in the collagen II autoimmune arthritis (CII AIA)-susceptible D1 strain mice revealed that the onset of disease was associated with a predominance of IgG2a autoantibody. In a comparative study, resistance in the B6 strain was associated with a deficient IgG2a autoantibody response. B6 IgG1, 2b, and 3 autoantibody responses generally overlapped those of arthritic D1 mice, and estimates of antibody crossreactivity and affinity were similar for both strains. In crosses between D1 and B6, arthritis developed only in those F1 mice with IgG2a autoantibody responses approximating or exceeding those in arthritic D1 mice. Additional studies with B6 and B10 strains suggested an alternate role for the IgG2b autoantibody response. In inbred strains with known genetic backgrounds, a dissociation between the magnitude of the total IgG autoantibody response and the percent of total as IgG2a was demonstrated. The H-2q, Ig-1c D1 strain was a high-total and high-percent IgG2a responder, while the H-2d, Ig-1c D2 strain was a low-total but high-percent IgG2a responder. The H-2b, Ig-1b B6 strain was a low-total and low-percent IgG2a responder, while the H-2b/q, Ig-1b/c (B6D1)F1 hybrid was a low-total but high-percent IgG2a responder. A further dissociation between high-percent IgG2a autoantibody responsiveness and the H-2 haplotype was demonstrated by the H-2 congenic B10.D2/n (H-2d, Ig-1b) strain, in which a low-percent IgG2a response was observed to differ from the D2 strain. High-percent IgG2a autoantibody responsiveness also appeared to be inherited as a dominant trait based upon high responses in all (B6D1)F1 hybrids and backcrosses to D1. These findings suggest that the H-2 haplotype is involved in the total IgG autoantibody response but that the relative fraction of the total response as IgG2a is independent of the H-2 haplotype and possibly related to Igh-C genes. C5-deficient SWR (H-2q, Ig-1c) mice were found to have a high total autoantibody response to mouse CII and IgG2a comparable to arthritic D1 mice, but these mice did not develop arthritis. Based upon these observations, we conclude that susceptibility to CII AIA requires the interaction of multiple genes, both major histocompatibility complex (MHC) and non-MHC, which influence the magnitude (total IgG) and the quality (IgG subclass) of the autoimmune response and the availability of appropriate mediators (C5) to initiate the inflammatory reaction.

Collagen-induced arthritis is an animal model of polyarthritis that can be induced in susceptible rats by immunization with native type II collagen (1). The development of arthritis is associated with high levels of both cell-mediated and humoral immunity to type II collagen (2) and the arthritic response appears to be due to collagen immunity. This animal model is of importance because collagen immunity has also been described in association with human rheumatoid arthritis (RA) 1 (3-6) and other rheumatic diseases (7,8). In addition, the histopathology of collagen-induced arthritis resembles that seen in human RA in that the lesion is one of synovial proliferation that progresses to pannus formation and results in marginal erosions with extensive destruction of cartilage. Radiographs of affected rat joints also show erosive changes similar to those seen in human RA (1).The mechanism by which arthritis develops in this model is unclear. It has been reported (9) that arthritis can be transferred from immunized arthritic and nonarthritic donor rats to nonimmunized syngeneic recipients with pooled spleen and lymph node cells. However, the specific cell type responsible for transfer of disease has not been identified; furthermore, neither cellular sensitivity nor antibodies to collagen could be detected in the arthritic recipients. We have been impressed with the invariable association of arthritis with high antibody levels to collagen and decided to attempt to transfer disease using serum. Early serum from rats at the time of onset of disease was chosen because of the marked difference in anticollagen antibody levels in arthritic as compared with nonarthritic donors (10) and the suggestion that early serum was essential to transfer of experimental autoimmune thyroiditis in rabbits (11). This serum, when fractionated with 50% ammonium sulfate and concentrated, proved to be effective in transferring disease. Having successfully transferred disease, we addressed the questions of (a) whether the serum factor could reproduce all of the histopathologic findings present in actively immunized arthritic rats, and (b) what component of serum was responsible for development of arthritis.

A B S T R A C T We have recently described a new animal model of arthritis induced by intradermal injection of a distinct type of collagen found in cartilage (type II collagen). Since immunologic sensitivity to collagen could play a role in the pathogenesis of this type II collagen-induced arthritis in rats, the ability of purified types of native collagens to induce cellular and humoral responses was quantified by antigeninduced tritiated thymidine incorporation into lymphocytes by collagen and passive hemagglutination, respectively. Rats injected intradermally with native heterologous or homologous type II collagens in adjuvant developed type-specific cellular as well as humoral reactivity. Types I and III collagens were less immunogenic than was type II. The latter collagen induced brisk cellular and humoral responses that were equivalent whether complete Freund's adjuvant or incomplete Freund's adjuvant were employed. Both responses could be induced by native type II collagens modified by limited pepsin digestion, indicating that they are not attributable to determinants in the telopeptide regions of the molecule. Thus, these studies demonstrate the unique immunogenic as well as arthritogenic properties of the type II collagen molecule and indicate that both result from a helical conformation of its structurally distinct a-chains. Further, they suggest that type II collagen may, by humoral or cellular mechanisms, provoke or perpetuate inflammation in other arthritic diseases.A preliminary account of part of this work was presented at