Cytokine mRNA Expression inMycobacteriam ulcerans-Infected Human Skin and Correlation with Local Inflammatory Response

Abstract

Cytokine mRNA expression in biopsies of Mycobacterium ulcerans-infected human tissue was investigated using real-time PCR, and the findings were correlated with the clinical stages of disease and histopathologies. A broad range of cytokine mRNAs were detected in 16 early nodules and 28 late-stage ulcers, including those for the Th1 cytokines tumor necrosis factor alpha (TNF-␣) and gamma interferon (IFN-␥) and the Th2 cytokine interleukin 10 (IL-10). IFN-␥ was strongly expressed in both nodules and ulcers, suggesting that a Th1 response begins early in the disease. There was a significantly higher expression of IL-8 and other proinflammatory cytokines in results from 32 biopsies with neutrophilia than in those from 12 biopsies without acute inflammation. Ten tissue samples containing granulomas showed high mRNA expression for IFN-␥, IL-1␤, IL-12p35, IL-12p40, IL-15, and TNF-␣ relative to 34 tissue samples without granulomas. These results suggest that the human immune response to M. ulcerans is similar to that seen with some other mycobacteria despite the presence of the toxin mycolactone in the tissues.

IFN-γ–Dependent Activation of Macrophages during Experimental Infections by Mycobacterium ulcerans Is Impaired by the Toxin Mycolactone

“…Our findings are in line with several studies with human BU patients suggesting that IFN-g is associated with protection (24,27,39,49). This cytokine was firstly suggested to play a role in the control of M. ulcerans infections by Gooding et al (24,39), who report that PBMCs from patients with past BU, but not from healthy contacts, display low capacity to produce IFN-g after stimulation with live M. ulcerans or Mycobacterium bovis bacillus Calmette-Guérin (BCG).…”

“…These results show that, as in human BU lesions (24,25,27), IFN-g is expressed in the infection foci of mice infected with M. ulcerans. Next, we decided to investigate the biological activity of this cytokine in experimental infections by comparing the proliferation of the different M. ulcerans strains in footpads of IFNg-deficient mice or wild-type (WT) counterparts.…”

“…When PCR analysis was used to quantify the expression of this cytokine in nodular or ulcerative BU lesions, Prévot et al (26) reported a higher expression of IFN-g in the nodular lesions while a lower expression was detected in the more severe ulcerative lesions. On the other hand, in a more recent study, Phillips et al (27), using a higher number of patients, reported a strong expression of IFN-g in both nodular and ulcerative lesions. Also in line with our findings, supporting therefore the existence of protective cellular-mediated immune and delayed-type hypersensitivity responses, associated with IFN-g production in the context of Th1 responses, when BU disease progresses to healing, granuloma formation occurs (3,46,(53)(54)(55), and the positivity of the Burulin skin test increases (56)(57)(58).…”

“…Although IFN-g has been suggested to be associated with resistance to BU (24,25,27), the role of this cytokine in M. ulcerans infections has not been experimentally addressed. We started by investigating whether IFN-g was expressed following M. ulcerans infection.…”

Mycolactone-Mediated Inhibition of Tumor Necrosis Factor Production by Macrophages Infected withMycobacterium ulceransHas Implications for the Control of Infection

“…It has been recently shown that M. ulcerans has an intramacrophage growth phase (84), which is in accordance with the occurrence of cell-mediated immunity and delayed-type hypersensitivity responses in BU patients (20,35,36,40,41,49,53,54,58,64,66,76,78,82,86,87). The correlation between the amounts of TNF produced by macrophages infected with different strains of M. ulcerans and the mycolactones produced by these strains, as well as the biological relevance of TNF in the progression of infection by M. ulcerans, is currently unknown.…”