Studies of pharmacological interventions and pathogenesis of rheumatoid arthritis

Abstract

Rheumatoid arthritis (RA) is a systemic inflammatory disease primarily affecting the joints. The chronic inflammation frequently results in joint destruction and various forms of physical impairment. T cells are believed to be of importance for the propagation of many cases of RA due to the association with certain types of HLA class 11, whose function is to present antigen to the T cell receptor. There is, however, evidence that also macrophages and B cells may be of prime importance in driving the inflammatory process in RA

In this thesis, an approach has been made to study immune functions in RA during treatment with two different anti-rheumatic drugs, intramuscular gold and tumour necrosis factor-(TNF)alpha-blockade with etanercept (a soluble TNFalpha-receptor), with the goal to learn more about RA pathogenesis. The mechanism of action of intramuscular gold treatment is not known but it has been suggested that gold may shift the immune system towards production of anti-inflammatory cytokines, rather than inducing a general immune suppression. We investigated the cytokine production in vitro in response to gold sodium thiomalate (GSTM), and found a stimulatory effect on monocyte dependent production of the and- inflammatory cytokine interleukin (IL)-10 along with a decrease of interferon-(IFN)gamma levels in corresponding supematants. In concordance with these results, there was an increased IL-10 production during GSTM treatment in RA patients. In addition, the in vitro effect of GSTM on IL-10 production from peripheral blood mononuclear cells (PBMC) predicted development of skin reactions during in vim treatment with GSTM, with low IL-10 production being associated with appearance of skin reactions. From these studies we conclude that intramuscular gold treatment has cytokine stimulating properties, and the stimulation of IL-1 0 production might have importance for the therapeutic effect of gold in RA- Moreover, the ability of RA patients to produce IL-1 0 in response to gold may influence the development of skin reactions.

RA T cells are hyporesponsive when stimulated with microbial antigens in vitro compared to T cells from the blood of healthy subjects. Activated monocytes/macrophages suppress T cell functions, possibly mediated through pro-inflammatory cytokines such as TNFalpha We investigated peripheral T cell reactivity in RA patients during etanercept therapy and found an increased T cell reactivity against microbial antigens and collagen type 11, an autoantigen. These findings indicate that T cell hyporesponsiveness in RA is, at least partly, TNFalpha-mediated and that TNFalpha-blockade may not only suppress but also stimulate certain aspects of antimicrobial immune defence and autoimmunity. The findings thus warrant further consideration of development of autoimmune reactions during TNFalpha-blockade therapy.

TNFalpha is also known to stimulate production of matrix metalloproteinases (MMPs), which are upregulated in the inflamed joint and highly associated with development of synovial degradation and joint erosions. During etanercept therapy, serum levels of both MMP-1 and MMP-3 were downregulated in parallel with the reduction of inflammatory parameters. Moreover, pre-treatment MMP-3 serum levels correlated with changes in disease activity during etanercept therapy.

Cytokine promoter polymorphisms are known to be associated with different levels of production of the same cytokine. This observation indicates that also intervention with a cytokine may differ in efficacy depending on genetic variations. Although TNFalpha-blockade is very efficient in ameliorating diseases activity in most of the treated patients with RA, about one third of the patients do not respond appropriately to this therapy and there are as yet no prognostic markers for clinical response. We analysed whether promoter polymorphisms of pro- and anti-inflammatory cytokine genes correlated with clinical response to etanercept. A combination of alleles conferring a normal TNFalpha production (-308 T1/T1) and high IL-10 production (-1087 G/G) was associated with good clinical responsiveness to etanercept. Another combination conferring high inflammatory capacity (A2 allele in intron 2 of the IL1 RN gene and rare C allele in codon 25 of the TGF131 gene) was associated with nonresponsiveness. Thus, genetic polymorphisms that influence the balance of cytokines that are of relevance for the course of RA seem to be associated with clinical outcome of etanercept therapy. This finding may be of value for further studies possibly promoting the use of cytokine polymorphisms as predictors for response to various biological agents in the future.