Interleukin 6 and interferon gamma haplotypes are related to cytokine serum levels in dogs in an endemic Leishmania infantum region

Abstract

Background: The Ibizan Hound is a canine breed native to the Mediterranean region, where leishmaniasis is an endemic zoonosis. Several studies indicate a low prevalence of this disease in Ibizan Hound dogs, whereas other canine breeds present a high prevalence. However, the underlying molecular mechanisms still remain unknown. The aim of this work is to analyse the relationship between serum levels of cytokines and the genomic profiles in two canine breeds, Ibizan Hound (resistant canine breed model) and Boxer (susceptible canine breed model).

Methods: In this study, we analyse the haplotypes of genes encoding cytokines related to immune response of Leishmania infantum infection in twenty-four Boxers and twenty-eight Ibizan Hounds apparently healthy using CanineHD DNA Analysis BeadChip including 165,480 mapped positions. The haplo.glm extension of haplo.score was used to perform a General Linear Model (GLM) regression to estimate the magnitude of individual haplotype effects within each cytokine.

Results: Mean levels of interferon gamma (IFN-γ), interleukin 2 (IL-2) and IL-18 in Boxer dogs were 0.19 ± 0.05 ng/ml, 46.70 ± 4.54 ng/ml, and 36.37 ± 30.59 pg/ml, whereas Ibizan Hound dogs present 0.49 ± 0.05 ng/ml, 64.55 ± 4.54 ng/ml, and 492.10 ± 31.18 pg/ml, respectively. The GLM regression shows fifteen haplotypes with statistically significant effect on the cytokine serum levels (P < 0.05). The more relevant are IL6-CGAAG and IFNG-GCA haplotypes, which increase and decrease the IL-2, IL-8 and IFN-γ serum levels, respectively.

Conclusions: Haplotypes in the IFNG and IL6 genes have been correlated to serum levels of IFN-γ, IL-2 and IL-18, and a moderate effect has been found on IL8 haplotype correlated to IL-8 and IL-18 serum levels. The results indicate that the resistance to L. infantum infection could be a consequence of certain haplotypes with a high frequency in the Ibizan Hound dog breed, while susceptibility to the disease would be related to other specific haplotypes, with high frequency in Boxer. Future studies are needed to elucidate whether these differences and haplotypes are related to different phenotypes in immune response and expression gene regulation to L. infantum infections in dogs and their possible application in new treatments and vaccines.

Keywords: Cytokine; Dog; Haplotype; Immune response; Leishmania; Regulatory mechanism; Resistance; Susceptibility.

Fig. 1

Serum levels of cytokines in Boxer (B) and Ibizan hound (I). Different P-values for cytokines are shown in figures a–e. a Interferon gamma (IFN-γ), b Interleukin 2 (IL-2), c Interleukin 6 (IL-6), d Interleukin 8 (IL-8), and e Interleukin 18 (IL-18). Squares represent LS means values for two breeds, and vertical lines represent standard deviation. Values for IL-8 and IL-18 are expressed in pg/ml, and for IFN-γ, IL-2, and IL-6 in ng/ml. Different p-values for cytokines are shown in figures a–e

Fig. 2

Effects of cytokines haplotype (IL6, IFNG)-serum levels (IFN-γ, IL-2, IL-18) interactions. Dots represent the expected serum values under the tested GLM for each cytokine haplotype (Predicted values for the basal/base haplotype are signalled with a solid line), sizes are according to their relative frequencies, total and breed specific. Those statistically significant haplotypes are indicated with an *. IFN interferon; IL interleukin