“Avaliação dos mecanismos imunológicos associados ao aumento da resistência de animais tratados com Talidomida frente à infecção com Brucella abortus”

Abstract

Brucellosis is a zoonotic disease caused by bacteria of the genus Brucella that infects humans and a wide variety of animals, especially cattle. In humans it causes undulant fever, endocarditis, arthritis and osteomyelitis while in animals causes abortion and infertility. This disease is considered the most prevalent zoonosis in the world, with more than 500,000 new cases reported annually. Only in Brazil, Brucellosis causes an estimated economic impact of $ 32 million annually. The immune response against Brucella involves different mechanisms of innate and acquired immunity among which IFN-y cytokine, typical of TH1 profile, and CD8+ T cells have an important role. IFN-y activates macrophages by inducing the production of radicals derived from oxygen and nitrogen essential to combat the pathogen and activate NK cells. Already, CD8+ lymphocytes lyse infected cells by destroying the pathogen or leaving it vulnerable to extracellular mechanisms of immunity. So, these mechanisms are essential for an effective infection control. Several studies have shown that thalidomide, a derivative of glutamic acid, is able to induce the formation of a TH1 profile with high production of IFN-y, and to co-stimulate and induce proliferation and cytokine production by CD8 + T lymphocytes. In fact, previous studies from our group demonstrated that previous treatment with thalidomide is able to increase the resistance of C57BL/6 mice against Brucella, coupled with the increase in cytokine production (IL-12 and IFN-y), nitric oxide and CD8+ T cells. Therefore, since the Thalidomide has a broad spectrum of actions, the objective of this study was to evaluate other immune mechanisms affected by Thalidomide and which are associated with increased resistance to the pathogen. Our focus is not the treatment with thalidomide itself, but undergird the development of new compounds or vaccine components that help in combating this important disease. As methodology, firstly was confirmed the bacterial load one week after infection in animals previously treated with Thalidomide. Then the profile of regulatory cells and cell proliferation were determined in splenocytes derived from treated and infected mice. Regarding innate immunity, the action of thalidomide was evaluated by the production of cytokines (IL-6 and TNF-α) and nitric oxide. Finally, we evaluated the influence of thalidomide on survival of animals "IFN-y Knockout” after Brucella infection and if the treatment with the drug is able to change the protection induced by vaccination with strain RB51 protection. As results, it was noticed a significant decrease in bacterial load of animals treated with thalidomide compared to untreated animals. This reduction was accompanied by an increase in lymphocyte proliferation and decrease in the percentage of regulatory T cells. With regard to macrophages, an increase in nitric oxide production in cells treated with the drug was seen after stimulation with bacteria. Finally, treatment with thalidomide was not able to confer higher level of protection to animals vaccinated with RB51 strain and did not change the life of animals "Knockout" for IFN-y infected with B. abortus. So, this study concludes that thalidomide is able to enhance the elimination of Brucella abortus in vivo, and that this enhancement depends on the IFN-y and nitric oxide as well as the reduction in the regulatory profile.