# Cortisol Regulates PD‐1 and IL‐12 in Canine Leishmaniasis

## TL;DR

This study shows that cortisol levels are elevated in dogs with leishmaniasis, which may affect immune responses and disease progression.

## Contribution

The study is the first to report HPA axis dysregulation in canine leishmaniasis and its link to immune markers.

## Key findings

- Cortisol levels were higher and ACTH levels were lower in dogs with leishmaniasis.
- Cortisol negatively correlated with PD-1 and IL-12 in infected dogs.
- Increased expression of iNOS, arginase-1, and PD-1 was observed in PBMC of infected dogs.

## Abstract

Canine visceral leishmaniasis (CanL) is a tropical zoonosis caused by Brazil's protozoan Leishmania (L.) infantum. Disorders in the hypothalamic–pituitary–adrenal (HPA) axis have been reported in human and experimental visceral leishmaniasis, but not yet in canine leishmaniasis. Cortisol is a steroid hormone that regulates several processes, including immune responses. This study investigated HPA axis disorders in dogs with visceral leishmaniasis and their link to clinical and immunological parameters. ELISA quantified serum levels of cortisol and adrenocorticotrophic hormone (ACTH) in 12 healthy dogs and 13 dogs with leishmaniasis. The expression of the enzymes inducible nitric oxide synthase (iNOS) and arginase‐1 and programmed cell death protein‐1 (PD‐1) were evaluated by flow cytometry in peripheral blood mononuclear cells (PBMC). Additionally, serum levels of the cytokines interleukin (IL)‐1β, IL‐6, IL‐10, IL‐12, interferon‐gamma (IFN‐γ), tumour necrosis factor‐alpha (TNF‐α), and transforming growth factor‐beta (TGF‐β) were quantified by capture Enzyme‐Linked Immunosorbent Assay (ELISA). Parasite load was quantified in peripheral blood and conjunctival swabs by real‐time polymerase chain reaction (qPCR). All parameters evaluated were correlated with serum cortisol. We observed an increase in cortisol, while ACTH levels were reduced in dogs with leishmaniasis. The expression of iNOS, arginase‐1 and PD‐1 was higher in the PBMC of dogs with leishmaniasis. Serum levels of the cytokines IL‐10, IL‐6, IL‐12, and IFN‐γ were increased in dogs with leishmaniasis. Cortisol showed a negative correlation with PD‐1 and IL‐12. Our findings suggest that infection natural with L. infantum in dogs may induce dysregulation of the HPA axis, leading to elevated serum cortisol levels and modulation of the immune response, as it is associated with immunological markers involved in disease pathogenesis. These results contribute to a better understanding of the pathogenic mechanisms of the disease.