TNFα inhibitors exacerbate Mycobacterium paratuberculosis infection in tissue culture: a rationale for poor response of patients with Crohn's disease to current approved therapy

Background The role of Mycobacteriumavium subspecies paratuberculosis (MAP) in Crohn's disease (CD) is increasingly accepted as evident by detection of the bacteria in the blood and intestinal tissue from patients with CD, and by supporting data from several open-label anti-MAP treatment studies. Tumour necrosis factor alpha (TNF alpha) monoclonal antibodies (anti-TNF alpha) have been widely used for CD treatment. Despite the short-term benefit of anti-TNF alpha in controlling CD symptoms, most patients suffer from detrimental adverse effects, including higher susceptibility to mycobacterial infections. Methods We investigated the effect of recombinant cytokines and anti-TNF alpha therapeutics on macrophages infected with clinical MAP strain isolated from CD patient blood. MAP viability was measured in macrophages pulsed with PEGylated and non-PEGylated anti-TNF alpha monoclonal antibodies at concentrations 0 to 50 mu g/ mL and with rTNF alpha, rIL-6, rIL-12, rIL-23 and IFN gamma at a final concentration of 1000 U/mL. Expression of proinflammatory cytokines was measured by RT-PCR following MAP infection. Results Both PEGylated and non-PEGylated forms of anti-TNF alpha increased MAP viability by nearly 1.5 logs. rIL-6 and rIL-12 induced MAP viability at 5.42 +/- 0.25 and 4.79 +/- 0.14 log CFU/mL, respectively. In contrast, rTNF alpha reduced MAP survival in infected macrophages by 2.63 logs. Expression of TNF alpha, IL-6 and IL-12 was upregulated threefold following MAP or M. tuberculosis infection compared with other bacterial strains (p<0.05), while expression of IL-23 and IFN gamma was not significant after MAP infection. Conclusion The data indicate MAP-positive patients with CD receiving anti-TNF alpha treatment could result in favourable conditions for MAP infection, which explains the poor response of many patients with CD to anti-TNF alpha therapy.