Lessons from helminth infections: ES-62 highlights new interventional approaches in rheumatoid arthritis

Abstract

Parasitic worms are able to survive in their mammalian host for many years due to their ability to manipulate the immune response by secreting immunomodulatory products. It is increasingly clear that, reflecting the anti-inflammatory actions of such worm-derived immunomodulators, there is an inverse correlation between helminth infection and autoimmune diseases in the developing world. As the decrease in helminth infections due to increased sanitation has correlated with an alarming increase in prevalence of such disorders in industrialized countries, this 'hygiene hypothesis' has led to the proposal that worms and their secreted products offer a novel platform for the development of safe and effective strategies for the treatment of autoimmune disorders. In this study we review the anti-inflammatory effects of one such immunomodulator, ES-62 on innate and adaptive immune responses and the mechanisms it exploits to afford protection in the murine collagen-induced arthritis (CIA) model of rheumatoid arthritis (RA). As its core mechanism involves targeting of interleukin (IL)-17 responses, which despite being pathogenic in RA are important for combating infection, we discuss how its selective targeting of IL-17 production by T helper type 17 (Th17) and γδ T cells, while leaving that of CD49b(+) natural killer (NK and NK T) cells intact, reflects the ability of helminths to modulate the immune system without immunocompromising the host. Exploiting helminth immunomodulatory mechanisms therefore offers the potential for safer therapies than current biologicals, such as 'IL-17 blockers', that are not able to discriminate sources of IL-17 and hence present adverse effects that limit their therapeutic potential.

Keywords: ES-62; IL-17; helminth immunoregulation; rheumatoid arthritis; γδ T cells.

Fig. 1

Excretory–secretory (ES)-62 is effective in the collagen-induced arthritis (CIA) model, but not in the collagen antibody-induced arthritis (CAIA) model. (a) DBA1J mice undergoing CIA (receiving collagen injections at days 0 and 21) were treated with ES-62 (2 μg, at days −2, 0 and 21), and clinical scores were recorded along with paw width, where significant protection was observed compared to phosphate-buffered saline (PBS)-treated mice. (▪ = PBS, n = 11; □ = ES-62, n = 11); *P < 0·05. (b) For the CAIA model, C57BL/6 mice were administered 2 mg of ArthritoMab antibody cocktail (MD Bioscience) on day 0 followed by a lipopolysaccharide (LPS) boost on day 3. Mice were treated with ES-62 (2 μg, daily from days −1 to 6) and arthritic scores and paw width were recorded (▪ = PBS, n = 7; □ = ES-62, n = 7).

Fig. 2

Excretory–secretory (ES)-62 targets γδ T cells but not natural killer (NK) T cells in collagen-induced arthritis (CIA). Mice were treated at days −2, 0 and 21 with phosphate-buffered saline (PBS) (▪) or ES-62 (□, 2 μg). Percentage of cells in lymph nodes and number of interleukin (IL)-17⁺ cells were quantified at the day of killing for γδ T cells (a) and CD49b⁺ NK (NK and NK T) cells (b) after 5 h of brefeldin A treatment at 37°C. Symbols represent responses of individual mice. *P < 0·05 by one-tailed t-test. Antibodies were used for fluorescence activated cell sorter (FACS) staining, according to the manufacturer's instructions: eBioscience (IL-17-peridinin chlorophyll (PerCP), γδ T cell receptor-fluorescein isothiocyanate (TCR-FITC), CD49b-antigen presenting cells (APC).

Fig. 3

Toll-like receptor (TLR)-4 expression is associated with interleukin (IL)-17⁻ γδ T cells in collagen-induced arthritis (CIA). Following determination of IL-17 expression by draining lymph node (DLN) cells from CIA mice following ex-vivo stimulation with phorbol myristate acetate (PMA) plus ionomycin, TLR-4⁺ cells (eBioscience) were determined according to appropriate isotype controls (tinted grey histograms) in γδ T cells and CD49b⁺ cells.

Fig. 4

A model of the mechanism of action of excretory–secretory (ES)-62 in modulating a complex network of dendritic cells (DC), B cells, CD4⁺ T cells and γδ T cell interactions to suppress pathogenic T helper type 1 (Th1) and Th17 responses in the collagen-induced arthritis (CIA) model. Natural killer (NK) cells are not affected by ES-62, suggesting that the ability of these cells to secrete IL-17 during infections would not be compromised. Expression of TLR-4 is shown by *; (*) = TLR-4 expression in some cell subsets.