Different populations of rheumatoid adherent cells mediate activation versus suppression of T lymphocyte proliferation

Immunopathogenesis and immunotherapy in rheumatoid arthritis: an area in transition

In years to come, new therapeutic modalities for the treatment of chronic arthritis will be launched for general clinical use. These therapies, until today only used in clinical studies, are based on knowledge obtained from animal models of chronic arthritis. This knowledge not only ushers therapeutic use in humans: in many settings, the animal studies have proven to be irreplacable tools to get insights into the pathogenesis of chronic arthritis. Rheumatoid arthritis (RA) shows a strong linkage of susceptibility to a certain epitope common to some HLA-DR beta chains; this immunogenetic linkage is the strongest evidence for specific, T-cell dependent immunity in the pathogenesis of the disease. Despite intense efforts, no unequivocal proofs of T-cell specificity or oligoclonality have been found in RA. Therapeutic efforts directed against T-cells or T-cell functions have also at the best showed partial effects. As compared to the local production of T-cell cytokines in the joint, monokine production is abundant. Therapies aimed at neutralizing the effects of the cartilage-devastating monokine TNF-a have showed remarkable results in small clinical trials. The possibility of increasing the presence of the regulatory cytokines IL-4, IL-10 and TGF-beta has also been explored, but only in animal studies. Immunology has also shed light on the mode of action of the commonly used 'disease modifying' drugs, and combinations of such drugs have shown increased potentials in recent clinical studies. The possibility of combining traditional anti-arthritic drugs with recent immunological tools seem promising for the future. This review discusses recent advances in the understanding of pathogenesis and delineate new therapeutic approaches for chronic arthritis from the point of view of the immunologically oriented clinician.

Rheumatoid arthritis

The immunopathogenesis of rheumatoid arthritis is discussed in two ways. First, we consider the major question of whether T cells are likely to drive the disease. Second--and assuming T cells to be important--we discuss available data on the components of the trimolecular complex (major histocompatibility complex class II-antigen-T-cell receptor), which are possibly involved in the disease. Our two main points are that the most important questions concerning the pathogenesis of rheumatoid arthritis require answers from immunointervention in patients, and that animal experiments can be increasingly used in interpreting current experiments in humans.

Effects of interferon-gamma treatment on the cutaneous DTH reaction in rats

The capacity of interferon-gamma (IFN-gamma) to induce class II histocompatibility antigens on different cell types including keratinocytes, is well known, but the impact of IFN-gamma on the immune response is still unclear. Lewis rats sensitized with dinitrofluorobenzene (DNFB) were injected with recombinant rat IFN-gamma (10(5) U) or phosphate-buffered saline (PBS) once daily on 3 successive days at the bases of the ears either before or after they were challenged on the ears. As expected, the PBS-treated animals showed about a 30% increase in ear thickness and there was an induced expression of class II antigens on the keratinocytes as judged by immunohistochemistry 72 h after challenge. Exogenously added IFN-gamma prior to DNFB challenge resulted in a significantly reduced ear swelling at 24 (p less than 0.01) and 48 h (p less than 0.05) after challenge. In this case the keratinocytes expressed class II antigens already at the time of challenge. When IFN-gamma injections were given during the contact allergic reaction there was no significant reduction of ear swelling until 72 h (p less than 0.01). At that time point there was a more pronounced expression of class II antigens on the keratinocytes compared with PBS-injected animals, due to the IFN-gamma treatment. These in vivo data support our previous observations that IFN-gamma may play a self-limiting role in certain immune responses.

Effects of sulfasalazine and a sulfasalazine analogue on the formation of lipoxygenase and cyclooxygenase products

A sulfasalazine analogue, 5'-(2,4-dichlorobenzoyl)2'-hydroxyphenylacetic acid (CL 42A), potently inhibited the formation of 5-lipoxygenase products (leukotrienes B4 and C4 and 5-hydroxyeicosatetraenoic acid) by human leukocytes. Half-maximal inhibition of leukotriene production was obtained with 5 and 10 microM CL 42A after stimulation with serum-treated zymosan or ionophore A23187, respectively. CL 42A was equipotent to nordihydroguaiaretic acid and about 50 times more potent than sulfasalazine and benoxaprofen in studies on the inhibition of LTB4 formation in leukocyte suspensions stimulated with serum-treated zymosan. Furthermore, CL 42A had no inhibitory effect on the production of 15-hydroxyeicosatetraenoic acid after incubation of human leukocytes with ionophore A23187 in the presence of exogenous arachidonic acid. Sulfasalazine inhibited the synthesis of 5-lipoxygenase products (5-hydroxyeicosatetraenoic acid and leukotriene B4: IC50 250 microM, leukotriene C4: IC50 100 microM) in a concentration-dependent manner but had no effect on 15-hydroxyeicosatetraenoic acid formation. The metabolites of sulfasalazine, sulfapyridine and 5-aminosalicylic acid, and the isomer, 4-aminosalicylic acid, were all less potent than sulfasalazine as inhibitors of leukotriene formation. Both CL 42A (IC50 20 microM) and sulfasalazine (IC50 500 microM) inhibited the synthesis of thromboxane B2 and hydroxyheptadecatrienoic acid in human platelet suspensions after arachidonic acid stimulation. However, while CL 42A inhibited cyclooxygenase, the inhibitory effect of sulfasalazine was exerted mainly on thromboxane synthase. The platelet formation of 12-hydroxyeicosatetraenoic acid was not inhibited by CL 42A whereas sulfasalazine had a weak inhibitory effect.

Effects of purified protein derivative (PPD)-activated syngeneic epidermal cells on a PPD-specific rat T-helper cell line

An important question in local immune regulation in the skin is how keratinocytes at inflammatory sites can modify a local T-cell response to antigens introduced via the skin. In the present study we investigated the effects of rat epidermal cells obtained from the site of a tuberculin reaction, on the proliferative response of a syngeneic purified protein derivative (PPD)-specific CD4+ T-cell line. Epidermal cell suspensions from the tuberculin-reactive ears contained 23-37% cells expressing class II transplantation antigens as judged by immunocytochemistry compared with 2-3% in normal epidermis. When comparing the capacity of these two different epidermal cell populations to induce a PPD-specific T-cell response in vitro, it was found that the PPD-reactive epidermal cells induced a lower T-cell response than did normal epidermal cells. This discrepancy cannot be explained by an infiltration of inflammatory cells into the epidermis of tuberculin-reactive ears. Our data indicate that epidermal cells modified during a delayed-type hypersensitivity reaction in vivo may suppress an antigen-specific T-cell proliferation.

Immunoregulation in arthritis. A review on synovial immune reactions in RA and in some experimental animal models for arthritis

Local synovial immune reactions have during recent years been characterized both in human arthritides, particularly in rheumatoid arthritis (RA), and in animal models for arthritis. Common characteristics of human RA on one hand and experimental adjuvant arthritis and collagen arthritis on the other hand, are induced expression of class II transplantation antigens on synovial cells close to the cartilage and presence of activated T lymphocytes in close proximity to these class II expressing cells. The present review aims to describe some implications of these and subsequent findings both concerning the analysis of the pathogenesis of RA and concerning some therapeutic implications derived from parallel studies on relevant features of the human RA and the respective animal models for arthritis.

Functional role in self reactivity for Ia antigens on murine synovial cells

Cultures of synovial cells from normal CBA mice were established after collagenase treatment of synovial tissue collected from the knee joint. Morphological studies using light and electron microscopy have shown that confluent monolayers are composed of 90% triangular or stellate dendritic cells with numerous microvilli and 5% secreting cells containing many dense granules. Less than 5% contaminating cells, such as fibroblasts or macrophages, are present. The class I and class II antigens of the major histocompatibility complex, detected by indirect immunofluorescence or complement-dependent cytotoxicity, are expressed on the cell surface of normal CBA synovial monolayers. Functional Ia antigens borne by synoviocytes are evidenced by the proliferative responses they elicit from syngeneic (or allogeneic) spleen cells after a 3-day co-culture. Similarly, monolayers of Ia+ synovial cells were obtained from both MRL/lpr mice, which spontaneously develop an autoimmune syndrome, and the control MRL/n mice. Spleen cells from young MRL/lpr exhibited significantly higher levels of blastogenesis in syngeneic co-cultures than those from MRL/n mice. Conversely, with advancing age the syngeneic proliferative responses declined minimally for MRL/lpr mice and were unchanged for MRL/n mice. These findings suggest that Ia+ synovial cells can effectively interact with syngeneic lymphocytes and may initiate autoimmune reactivity.

Reactivity of monoclonal anti-type II collagen antibodies with cartilage and synovial tissue in rheumatoid arthritis and osteoarthritis

Monoclonal antibodies to 3 different epitopes on native type II collagen were used for immunohistochemical analysis of antigenic determinants that are exposed in the cartilage and synovial tissue obtained from patients with rheumatoid arthritis (RA) and osteoarthritis (OA). Two of the monoclonal antibodies reacted with cartilage from both OA and RA joints, but not with that from normal joints. The third monoclonal did not stain any of the cartilage sections. The 2 positive antibodies also reacted with cartilage fragments in the synovial tissue of both RA and OA joints, and in RA pannus tissue, the antibodies showed intracellular staining in many class II transplantation antigen-expressing synovial cells lying close to the damaged cartilage.