Local Increase of Arginase Activity in Lesions of Patients with Cutaneous Leishmaniasis in Ethiopia

The leishmaniases are a complex of diseases caused by Leishmania parasites. Currently, the diseases affect an estimated 12 million people in 88 countries, and approximately 350 million more people are at risk. The leishmaniases belong to the most neglected tropical diseases, affecting the poorest populations, for whom access to diagnosis and effective treatment are often not available. Leishmania parasites infect cells of the immune system called macrophages, which have the capacity to eliminate the intracellular parasites when they receive the appropriate signals from other cells of the immune system. In nonhealing persistent leishmaniasis, lymphocytes are unable to transmit the signals to macrophages required to kill the intracellular parasites. The local upregulation of the enzyme arginase has been shown to impair lymphocyte effector functions at the site of pathology. In this study, we tested the activity of this enzyme in skin lesions of patients presenting with localized cutaneous leishmaniasis. Our results show that arginase is highly upregulated in these lesions. This increase in arginase activity coincides with lower expression of a signalling molecule in lymphocytes, which is essential for efficient activation of these cells. These results suggest that increased arginase expression in the localized cutaneous lesions might contribute to persistent disease in patients presenting with cutaneous leishmaniasis

Frequency of CD4⁺ and CD8⁺ T cells in PBMCs and biopsies of LCL patients.

<p>The frequencies of CD4⁺ and CD8⁺ T cells was determined in cells isolated from the blood and from the biopsies of LCL patients (n = 15) by flow cytometry. (A) % of CD4⁺ T cells; (B) % of CD8⁺ T cells; (C) ratio of CD4/CD8. Values represent median with interquartile range. Statistical significance was determined by a two-tailed Mann-Whitney test, ns = not significant.</p

Frequency of neutrophils and monocytes in PBMCs.

<p>PBMCs were isolated by density gradient from the blood of controls (n = 10) and LCL patients (n = 15) and the frequencies of CD15⁺ (A), CD14⁺ (B) cells and the ratio of CD15/CD14 (C) were determined by flow cytometry. Values represent median with interquartile range. Statistical significance was determined by a two-tailed Mann-Whitney test, ns = not significant.</p

Ratio of CD4/CD8⁺ T cells in PBMCs isolated from controls (n = 10) and LCL patients (n = 12).

<p>Values represent median ± sem.</p

Arginase-expressing cells in biopsy are neutrophils.

<p>The phenotype of arginase-expressing cells in homogenates of skin biopsies was determined by flow cytometry by using a combination of antibodies against CD14, CD15 and arginase. Data show the results of one representative experiment out of three independent experiments.</p

Clinical data.

<p>nd = not done.</p

Arginase-expressing cells in PBMCs are neutrophils.

<p>PBMCs were isolated by density gradient from the blood of LCL patients. The phenotype of arginase-expressing cells was determined by flow cytometry. (A) Dot plot profile of CD15⁺ arginase⁺ cells; (B) dot plot profile of CD14⁺ arginase⁺ cells; (C) dot plot profile of forward (FSC) and side scatter (SSC). Data show the results of one representative experiment out of 15 independent experiments. Isotype control for arginase: 0.98%.</p

CD3ζ and CD8 MFI in PBMCs and biopsies of LCL patients.

<p>The MFI of CD3ζ in CD8⁺ T cells (A) and MFI of CD8 molecule (D) were compared between cells isolated from the blood and from the biopsies of LCL patients (n = 12) by flow cytometry; (B) representative histogram of MFI of CD3ζ in CD8⁺ T cells (open histogram = biopsies, closed histogram = PBMCs); (E) representative histogram of MFI of CD8 (open histogram = biopsies, closed histogram = PBMCs); (C) % decrease in CD3ζ MFI in CD8 (black bar = median); (F) % decrease in CD8. Statistical significance was determined by a Wilcoxon paired test.</p

CD3ζ and CD4 MFI in PBMCs and biopsies of LCL patients.

<p>The MFI of CD3ζ in CD4⁺ T cells (A) and MFI of CD4 molecule (D) were compared between cells isolated from the blood and from the biopsies of LCL patients (n = 12) by flow cytometry; (B) representative histogram of MFI of CD3ζ in CD4⁺ T cells (open histogram  =  biopsies, closed histogram = PBMCs); (E) representative histogram of MFI of CD4 (open histogram = biopsies, closed histogram = PBMCs); (C) % decrease in CD3ζ MFI in CD4 (black bar = median); (F) % decrease in CD4. Statistical significance was determined by a Wilcoxon paired test.</p

Arginase activity in skin lesions from controls and LCL patients.

<p>Skin biopsies from controls (n = 6) and LCL patients (n = 10) were homogenized and the activity of arginase was measured by enzymatic assay. Values represent median with interquartile range. Statistical significance was determined by a two-tailed Mann-Whitney test.</p