**Acknowledgements**

*Parasitology and Microbiology Research*

development [39].

production [41].

of active disease in dogs with VL.

involved with hypergammaglobulinemia [33].

IL-6 expression increases in dogs with active visceral leishmaniasis and may be a useful marker for active disease [33, 35]. Increased IL-6 production is not directly related to anti-*Leishmania* antibody titers, suggesting that other cytokines may be

As shown in this work, it was observed that there was correlation of IL-6 expression between stages I and III of bone marrow aspirate of dogs infected with CVL. IL-6 production in dogs with active leishmaniasis appears to be associated with severe disease [33]. This statement converges with the findings in this study, as the dogs used in the control group were mostly stage II and III. IL-6 is essential for

TNF-α concentration was higher in infected dogs than in the control group, as detected by de Lima et al. [33]. CVL susceptibility is closely associated with downregulation of key cytokines such as IFN-γ, TNF-α, and IL-17A, thus impairing iNOS activation and NO production and favoring parasite replication and disease

The increased activity of TNF-α in the liver of infected dogs compared to healthy canines has been reported [37, 40]. Higher TNF-α levels in infected dogs indicate that the presence of *L. infantum* induces an immune response with relevant

Studies suggest that decreased survival of L. *infantum* in canine macrophages is associated with increased TNF-α and IFN-γ production and decreased IL-10

In dogs naturally infected with *L. infantum*, increased hepatic TNF-α may be associated with increased parasite load on this organ [42]. The cytokines IL-2, IL-4, IL-10, IFN-γ, TNF-α, and IL-12 may be used as markers in epidemiological studies conducted in endemic areas to distinguish between different clinical forms of VL [15]. However, Lima et al. [33] indicate that TNF-α is not considered a good marker

A study has reported a significant relationship between bone marrow IL-4 detection in naturally infected dogs with and without clinical signs and disease severity, suggesting that IL-4 production is associated with pathology [43]. Increased expression of IL-4 cytokine is associated with both severe clinical signs and a high parasitic index on skin lesions [44]. In bone marrow aspirates, IL-4 was

The study points to evidence that IL-4 cytokine polymorphism may contribute

Antibody levels were positively correlated with IL-4 expression (rs = 0.5997; p = 0.0040). IgG is also linked to chronic infection in patients with VL, where high levels of IgG are predictive of the disease. This finding is in line with the study by Lima et al. [33] suggesting that other cytokines, such as IL-10 or IL-4, may be associated with hypergammaglobulinemia observed in dogs with CVL. Previous studies have detected increased serum IgG levels in symptomatic dogs compared with healthy dogs and are related to pathophysiological disorders and active disease [33]. Response to natural infection of *L. infantum* is linked to the presence of IgG [43] and *Leishmania*-specific IgM antibodies that can be detected in infected dogs [46]. Some studies have reported that increased total protein is frequent in dogs infected

elevated in naturally infected dogs with more severe symptoms [43].

with visceral leishmaniasis due to increased antibody production [47, 48].

These results may contribute to a better understanding of the immune response in dogs infected with *L. infantum*. Antibody levels were positively correlated with

to innate immunity to *L. infantum* infection [45].

terminal B-cell differentiation and immunoglobulin production [38].

TNF-α expression when the protozoan is present [40].

**110**

**5. Conclusion**

This research received grants from the Mato Grosso Research Support Foundation (FAPEMAT No. 299032/2010) and from the National Council for Scientific and Technological Development (CNPq No. 447218/2014–0 and No. 305725/2018–1), in Brazil.
