Parasite-mediated down-regulation of collagen-induced arthritis (CIA) in DA rats

Abstract

Microbial infection can impact on the course of autoimmune disease, both in disease-inducing and disease-protecting capacities. Here we investigated if infection with Trypanosoma brucei brucei (Tbb), the protozoan causative agent of African Sleeping Sickness, could ameliorate the course of CIA in the Dark Agouti rat, an experimental model which shares many features with human rheumatoid arthritis. Infection of animals with living, but not inoculation with dead Tbb resulted in complete or significant reduction of clinical arthritic symptoms. Infection prior to collagen immunization was more effective than a later treatment, and this effect was related to the level of parasitaemia. Using reverse transcriptase-polymerase chain reaction we detected an increase in interferon-gamma mRNA in the draining lymph nodes of Tbb-treated animals relative to controls at day 28 after disease induction. Transforming growth factor-beta could be detected in the lymph nodes in four out of six animals that had received Tbb. In the joints, immunohistochemistry revealed reduced production of tumour necrosis factor-alpha in Tbb-treated animals relative to controls. The most striking difference between Tbb-infected and control groups, as measured by ELISA, was the down-regulation of anti-collagen II IgG antibody responses in parasite-infected animals. We conclude that live parasites can exert an immunomodulatory and protective effect in CIA in which several mechanisms may work in parallel, although the almost complete down-regulation of the anti-collagen antibody response may alone explain the protective effect in CIA. The described model may be useful in further attempts to use the mechanisms involved in parasite immune defence to prevent and treat certain autoimmune conditions.

Fig. 1

(a) Infection of Trypanosoma brucei brucei (Tbb) before or on the day of CIA induction ameliorates CIA disease course. (a) Infection with Tbb was initiated on day 0 (n = 7), day 7 (n = 7) and compared with dead Tbb given day 0 (n = 6) and untreated CIA controls (n = 9). P < 0·01 for the Tbb day 0-treated group versus the CIA control group analysing the accumulated score (area under curve) for each animal, analysed using the Kruskall–Wallis statistical test followed by Dunn's method. (b) Infection of Tbb day −7 (n = 8) relative to control CIA group. P = 0·0004 for the accumulated score comparing live Tbb with CIA control group using Mann–Whitney analysis. □, Control; ▪, live Tbb day 0; Δ, dead Tbb day 0; •, live Tbb day 7.

Fig. 3

Anti-collagen II IgG antibody titres are reduced in the serum of Trypanosoma brucei brucei (Tbb)-infected rats. Serum collected at days 21 (□) and 28 (▪) p.i. for the experiment described in Fig. 2 were analysed by ELISA. CIA was induced in all animals at day 0 and animals were treated with live Tbb on day 0 (n = 9), dead Tbb (n = 6) or live Tbb on day 7 (n = 7). **P < 0·01; ***P < 0·001 relative to the CIA control group on each respective day, as analysed by anova using Bonferroni/Dunn post hoc test. At day 21 P = 0·076 between live day 7 and live day 0 treatment.

Fig. 2

Tumour necrosis factor-alpha (TNF-α) production in the synovial membrane. Rats were immunized with bovine CII (bCII)/Freund's incomplete adjuvant (FIA) and were treated with live Trypanosoma brucei brucei (Tbb) intraperitoneally (n = 3) the same day or were left untreated (n = 3). After 21 days the synovial membrane of the patella was taken and analysed for TNF-α immunohistochemically (see also Table 3). The pattern of TNF-α staining in the synovial membrane close to the cartilage is depicted for CII/FIA rats untreated (a) or with a Tbb (day 0) infection (b). The positions of the joint space (JS), synovial membrane (SM) and bone (B) are indicated.