Lactobacillus casei suppresses experimental arthritis by down-regulating T helper 1 effector functions

Abstract

Although the beneficial effects of probiotics on wide variety of diseases have been shown, little is known about how probiotics modulate the immune system. In this study we elucidated the underlying mechanisms how Lactobacillus casei (L. casei) protects against rheumatoid arthritis (RA) progression by investigating the effector functions of CD4⁺ T cells. Oral administration of L. casei suppressed collagen-induced arthritis (CIA) and reduced paw swelling, lymphocyte infiltration and destruction of cartilage tissue. L. casei administration reduced type II collagen (CII)-reactive proinflammatory molecules (IL-1β, IL-2, IL-6, IL-12, IL-17, IFN-γ, TNF-α and Cox-2) by CD4⁺ T cells. L. casei administration also reduced translocation of NF-κB into nucleus and CII-reactive Th1-type IgG isotypes IgG2a and IgG2b, while up-regulating immunoregulatory IL-10 levels. Our results suggest that oral administration of L. casei suppresses the type II collagen-reactive effector function of Th1-type cellular and humoral immune responses in arthritic inflammation.

Introduction

Rheumatoid arthritis (RA) is an autoimmune disorder characterized by chronic inflammation of the synovial membrane of joints, mononuclear cell infiltration, cartilage destruction and loss of articular cartilage (Smolen and Steiner, 2003). Inflammatory cytokines including IL-1β, TNF-α, IFN-γ, IL-6, IL-12 and IL-17 play a central role in the inflammatory processes involved in the pathogenesis of RA (Arend, 2001, Feldmann et al., 1996, Smolen and Steiner, 2003). Current treatments for RA employ immunosuppressive agents, nonsteroidal anti-inflammatory drugs (NSAIDs) and disease-modifying anti-rheumatic drugs (DMARDs). Although these reagents are beneficial in reducing inflammation and tissue destruction, adverse side effects limit their use in arthritis patients presenting diverse pathological symptoms (Kovarik et al., 1997, Smolen and Steiner, 2003). For example, methotrexate (MTX), a frequently used anti-rheumatic drug, inhibits proinflammatory cytokine production, but has a number of toxic side effects including nausea, vomiting, stomatitis, liver function abnormalities, blood count abnormalities, lung problems, and hair loss (Lorenzi et al., 2000, Ranganathan et al., 2003).

Probiotics have been defined as “live microorganisms which, when administrated in adequate amounts, confer a health benefit on the host” (Isolauri et al., 2001, Sanders, 2003). Recent studies suggested important roles of intestinal microflora in the development of arthritis and intestinal inflammation (Eerola et al., 1994, Nieuwenhuis et al., 2000, Sartor, 1997). In addition, the beneficial effects of probiotics have been tested in inflammatory autoimmune disease such as type I diabetes mellitus, rheumatoid arthritis and encephalomyelitis (EAE) (Kato et al., 1998, Maassen et al., 1998, Matsuzaki et al., 1997).

The therapeutic effect of Lactobacillus casei (L. casei) on RA has been studied in a DBA/1 mice model without detailed information on its action mechanism (Kato et al., 1998). CD4⁺ T cells play key roles in controlling and driving immune responses against CII and are involved in the initiation and development of RA (Holoshitz et al., 1983, Schulze-Koops and Lipsky, 2007). Indeed, modulation of T cell activity by anti-CD4 antibody or cyclosporine A suppressed the incidence and severity of RA (Bentin, 1995, De Keyser et al., 1995, Herzog et al., 1989, Walker et al., 1989).

In this study, we investigated how L. casei suppressed the inflammatory immune responses of RA by testing the effect of L. casei on the effector functions of CD4⁺ T cells. We found that L. casei administration suppressed progression of RA by reducing collagen-reactive effector function of Th1 cells, which is accompanied by reduced proinflammatory molecules, inhibition of nuclear translocation of NF-κB and lowered Th1-type serum IgG2a and IgG2b levels.