Is persisting antigen responsible for the chronicity of experimental allergic arthritis?

Changes of immunoregulatory properties and induction of autoimmune reactivity to cartilage in rabbits with antigen-induced arthritis

The chronicity of the antigen-induced arthritis is characterized as dependent on the development of cell-mediated immunity to the antigen, but the exact mechanisms underlying are unclear. We have evidenced decreased suppressor and increased helper cell potential in the early phase of arthritis as result of the immunization procedure. In the late phase of arthritis proliferative responses of spleen lymphocytes to cartilage proteoglycans were revealed which were neither present in immunized animals without arthritis induction nor in the early phase of arthritis. The changes of the regulatory properties on the T-cell level are probably responsible for the transition of acute arthritis into the chronic stage. The deficiency of an effective suppression and/or the increased helper cell potential results in the activation of B- and T-lymphocytes with increased cell-mediated and humoral immune responsiveness to the antigen maintaining the inflammatory process for a long time. In this situation the release of cartilage proteoglycans during the acute joint reaction induces autoimmune responses against cartilage which could contribute to the chronification of inflammation and to cartilage degradation.

The relationship between cell-mediated immunity and cartilage degradation in antigen-induced arthritis in the rabbit

The relative contributions of cellular and humoral immunity to cartilage destruction in chronic arthritis has been investigated in a model of chronic synovitis in the rabbit. In this model, antigen-induced arthritis, immunization with ovalbumin in Freund's complete adjuvant (FCA) followed by intra-articular injection of this protein produces a chronic synovitis associated with loss of proteoglycan from articular cartilage. In addition, the synovial lining cell population is metabolically activated. Similar treatment of animals immunized with ovalbumin in Freund's incomplete adjuvant (FIA) produced a resolving arthritis which initially (over the first 7 days) appears to be identical to that in FCA-immunized animals, apart from the lack of activation of synovial lining cells. Following this initial synovitis the joints return to apparent normality apart from a persistent 'low grade' synovitis consisting mainly of a plasma cell infiltrate. The most striking finding in the FIA-immunized animals is the rapid loss (greater than 30% by day 7) and recovery of proteoglycan from the matrix of articular cartilage. These findings show that the perpetuation of chronic destructive synovitis in the rabbit requires the presence of active cellular immunity.

Significance of cell-mediated and humoral immunity in the acute and chronic phase of antigen-induced arthritis in rabbits

In the course of antigen-induced arthritis of rabbit cell-mediated and humoral immune responses were repeatedly tested in order to prove their significance for the acute and chronic phase of inflammation. The arthritis was monitored during the progression of the inflammation by means of the joint swelling and at the end of experiments by histological evaluation of synovitis and cartilage degradation. Following the arthritis induction a strong increase of specific antibodies and of circulating immune complexes was evident. The correlations between antibody levels and joint swellings confirmed that the local formation of immune complexes is responsible for the initiation and perpetuation of arthritis. In the early phase after immunization the responsiveness of lymphocytes to antigenic and mitogenic stimulation was increased, in the late chronic phase of arthritis proliferative responses of lymphocytes to cartilage matrix components were revealed. No direct correlations could be demonstrated between any cell-mediated immune response and the severity of arthritis. The hyperreactivity of cell-mediated immunity is suggested to be responsible for the transition of the acute arthritis into the chronic stage. The deficiency of an effective suppression results in the activation of B-lymphocytes with increased production of antibodies, maintaining the inflammatory process for a long time. Under these conditions the release of cartilage matrix components during the acute joint reaction induces autoimmune responses against cartilage, which could contribute to the chronification of arthritis and to cartilage degradation.

Electrical charge of the antigen determines its localization in the mouse knee joint. Deep penetration of cationic BSA in hyaline articular cartilage

Intraarticular injection of cationic bovine serum albumin (BSA) induces a chronic arthritis in immunized mice, whereas the negatively charged native BSA fails to cause a protracted joint inflammation. In this study the authors examined the role of antigenic charge as a determinant of antigen retention and exact localization within the knee joint. Immune and nonimmune mice received an intraarticular injection of either radiolabeled native BSA (125I-BSA) or charge-modified BSA rendered cationic by amidation (aBSA), and autoradiographs were prepared of whole joint sections at various days after injection. As has been shown in the rabbit, the retention of the negatively charged native BSA is largely dependent upon the presence of antibodies. In nonimmune mice the radiolabeled antigen was hardly detectable after Day 1. In immune mice antibody-mediated retention of BSA was found in the ligaments and fibrous cartilage structures of the joint but appeared to be absent at the hyaline cartilage. In contrast, large amounts of the cationic aBSA were retained at all collagenous structures of the joint, the most striking observation being the deep penetration in the dense hyaline cartilage. This was found both in immune and nonimmune mice, which indicates that the deep penetration was not due to cartilage damage occurring under inflammatory conditions. With different dosages of aBSA it was found that the presence of antibodies may modulate the retention pattern in immune mice. Deep diffuse penetration into the dense hyaline cartilage, together with some surface labeling, was observed after injection of a high dose (60 micrograms), whereas mere surface labeling was found with the low dose (6 micrograms). Distinct superficial labeling was not seen in nonimmune mice, which suggests that this pattern represents immune complex formation at the cartilage surface. Immunofluorescence studies on undecalcified whole joint sections confirmed the deep penetration of the cationic antigen and supported the presence of immune complexes at the cartilage surface, because intense complement and Ig staining was detectable at this site. Our data indicate that antigenic charge determines the antigen retention in the joint both quantitatively and qualitatively. Negatively charged native BSA has no affinity for cartilage, high amounts of antibodies are needed for its retention in the joint, retention by this immune complex formation is largely restricted to the loose collagenous tissues, and the capacity to retain anionic antigen in the joint is therefore low.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on increased vascular permeability in the pathogenesis of lesions of connective tissue diseases: I. Experimental hyperlipidaemia and immune arthropathy

In order to investigate the known associations between hyperlipidaemia and various rheumatic complaints, immune arthritis and hyperlipidaemia have been induced concurrently in rabbits. The results obtained show that: (1) Rabbit apolipoprotein B-containing lipoproteins (LpB), which are normally virtually excluded from joint fluid, gain access to the inflamed joint in the serous effusion and serve as intrinsic indicators of altered local permeability to macromolecules. (2) Much of the LpB entering the joint space is taken up by the phagocytic cells and, following intracellular hydrolysis, leaves a lipid residue. In some chronically affected joints these residues are modified so as to give rise to crystalline cholesterol and its esters. Such crystals may serve as a chronic irritant in the joint. (3) In addition intact LpB is found sequestered in the superficial layers of intra-articular collagenous structures of the challenged joint in a distribution identical with that of similarly sequestered immune complexes and complement, suggesting altered permeability of these intra-articular structures also.

Chronic inflammatory reactions in the guinea-pig peritoneal cavity induced by continuous local PPD stimulation. Immune status dependency of the accumulation of lymphocytes and eosinophils

A chronic inflammation model is described which allows the study of the relationship between the level of specific cell-mediated and humoral immunity to the triggering antigen, and the presence of cells or mediators in the inflammatory exudate. In the present study special attention is paid to the participation of lymphocytes and eosinophils. Normal or FCA-pre-immunized guinea-pigs received repeated intraperitoneal injections with PPD for periods up to 21 weeks. In non-pre-immunized animals the inflammation was characterized by a strong accumulation of eosinophils, whereas only a few lymphocytes were present. In contrast, the FCA-pre-immunized guinea-pigs showed a strong lymphocytic accumulation in the absence of eosinophils. Both peritoneal inflammations were shown to remain dependent on the continuous PPD administration. Therefore, the participation of either lymphocytes or eosinophils could be directly correlated to differences in the specific immune status. Both experimental groups developed similar strong anti-PPD antibody responses as assessed by haemagglutination and passive cutaneous anaphylaxis. Only the FCA-pre-immunized guinea-pigs, however, showed strong cell-mediated immunity. The development of CMI to the continuously administered antigen appears to be a prerequisite for the accumulation of lymphocytes, while it seems to prevent antibody-mediated eosinophil accumulation.

Immune elimination and immune retention: the relationship between antigen retained in the foot and the elicitation of footpad swelling

We determined whether (1) long term antigen retention is present in distal sites after footpad challenge of immune mice; (2) if antigen retained in the foot is selectively localized; and (3) if the foot is adversely affected by the retained antigen. Mice immune or non-immune to human serum albumin (HSA) were injected in the hind footpads with 125I-HSA. In immune mice rapid clearance of radiolabel occurred in the liver, lungs, kidney, blood and urine but radiolabel was retained in the hind feet, draining lymph nodes and spleen. Non-immune mice rapidly cleared radiolabel from these sites. Autoradiography revealed that most of the radiolabel in the feet was in flexor tendons and tendon sheaths. Electron microscope autoradiography indicated that antigen was associated with collagen at the tendon surface, but not with cells or cell processes. Radiolabel solubilized from the feet, lymph nodes and spleen could be specifically precipitated with rabbit anti-HSA. Histological examination of the tendon and surrounding tissues did not show that retained antigen was causing inflammation or chronic tissue damage. Nanogram levels of antigen could elicit swelling in the sensitized foot even if the antigen was injected at a remote site, but mice immunized by other routes or against other antigens did not show footpad swelling. Antigen retained on collagenous tissues may induce hypersensitivity and thus play a role in rheumatic diseases.

Immune synovitis in rabbits. Effects of differing schedules for intra-articular challenge with antigen

The effects of varying intra-articular (ia) doses of bovine serum albumin (BSA) antigen on immune synovitis in rabbits have been investigated. Chronic synovitis, characterized by mononuclear cell infiltration in synovial tissues, was induced by a single ia challenge with BSA in sensitized rabbits. However, cartilage and bone erosions and pannus formation were rarely observed. By varying the number and magnitude of the BSA challenges, lesions with different characteristics were observed at different times of analysis of joint pathology. In 3- to 10-week studies, multiple ia challenges with BSA produced lesions characterized by severe cartilage and bone changes; polymorphonuclear leukocyte (PMN) exudates; and mononuclear cells and, sometimes, PMNs in synovial tissues. Substantial increases in knee widths and synovial tissue weights also observed. By increasing the frequency of ia injections, more severe changes were produced more rapidly, so that within a 3-week period, the animals also experienced pain and were unable to fully extend their antigen-challenged knees. Some of the lesions observed in immune synovis resembled those in rheumatoid arthritis (RA). However, the presence of large numbers of PMNs in synovial tissue under certain conditions suggests some possible differences between the pathogenesis of experimental synovitis and RA.