Cutaneous leishmaniasis in naturally infected dogs is associated with a T helper-2-biased immune response

Skin lesions are a frequent manifestation of Leishmania infantum infections in Mediterranean countries. This study demonstrates by real-time reverse transcriptase-polymerase chain reaction the local cytokine response in skin biopsies from Leishmania-infected dogs (n=10). As controls, we investigated skin biopsies from healthy (n=10) and fleabite hypersensitive dogs (n=10). We established a quantitative PCR to determine the parasite burden in biopsies. The objective was to elucidate whether a correlation exists between parasite number, histologic response, and T helper-1 (TH1)/T helper-2 (TH2) cytokine expression in lesional skin of naturally infected dogs. In Leishmania-infected dogs, interleukin-4 (IL-4), tumor necrosis factor alpha (TNF-alpha) and interferon-gamma (IFN-gamma) messenger RNA production was significantly higher than controls. Furthermore, dogs with a high Leishmania burden had a significantly higher IL-4 expression, whereas no difference was noted with regard to expression of other cytokines. By comparing the pattern of inflammation and cytokine expression, a clear trend became evident in that levels of IL-4, TNF-alpha, and IFN-gamma were elevated in biopsies with a periadnexal nodular pattern and in biopsies where the severity of the periadnexal infiltrate was equal to the perivascular to interstitial infiltrate. Expression of IL-4, IL-13, and TNF-alpha was slightly increased in biopsies where plasma cells prevailed on lymphocytes, whereas expression of IFN-gamma was moderately higher when lymphocytes were predominating. In summary, the present study demonstrates that the local immune response in naturally occurring leishmaniasis includes TH1 as well as TH2 cytokine subsets. Furthermore, respective data suggest that increased expression of the TH2-type cytokine IL-4 is associated with both severe clinical signs and a high parasite burden in the skin lesions.