Expression of IFN-γ, TNF-α, IL-10 and TGF-β in lymph nodes associates with parasite load and clinical form of disease in dogs naturally infected with Leishmania (Leishmania) chagasi

American visceral leishmaniasis is a zoonosis of the New World. Dogs are the main reservoir of the disease and there is much interest in the understanding of mechanisms implicated in protection against canine infection. Nevertheless, most studies in dogs have not been carried out in organs that are targets of infection. This work is first to report the profile of cytokines and parasite burdens, as determined by real-time PCR, in the lymph nodes of dogs naturally infected with Leishmania chagasi. With this purpose, 18 mongrel dogs were divided in three groups: control non-infected dogs (n = 6) and naturally infected animals with L. chagasi, asymptomatic (n = 6) and symptomatic (n = 6). Parasite burden in lymph nodes was 73-fold greater in symptomatic than asymptomatic animals. Prescapular lymph nodes of asymptomatic dogs had the highest expression of IFN-γ and TNF-α and low parasite burden, indicating that these cytokines play a role in protection against infection. Highest expression of IL-10 and TGF-β and high parasite burden were observed in symptomatic dogs, suggesting a role for these cytokines in the progression of disease. Hence, the balance of expression of IFN-γ and TNF-α (protective) and IL-10 and TGF-β (disease progression) in lymph nodes determine parasite burden and clinical expression in naturally infected dogs.