Characterization of the early immune response against intranasal Brucella infection in mice

Résumé

Brucellae are alpha-proteobacteria which induce brucellosis, a worldwild zoonotic disease infecting mammals, including humans. B. melitensis and B. abortus are the species the most often isolated in human brucellosis. Inhalation of airborne agents, ingestion of contaminated products and contact between a contaminated fluid or organ with a cutaneous lesion constitute the main natural routes of transmission. Up to now, no fully efficient prophylactic or therapeutic treatments are available, leading to serious economic losses and public health problems. Despite recent progress in mouse models of brucellosis, very little is known about the first steps of Brucella infection in vivo. Here we studied the Brucella melitensis 16M strain, that infects goat and sheep, and we investigated the immune response of mice following intraperitoneal (i.p.), intranasal (i.n.) or intradermal (i.d.) infection. The main objectives were to compare (i) the dissemination of bacteria after a primary infection, (2) the immunity required to control a primary infection, (3) the virulence gene essentiality, and (4) the lymphocyte populations indispensable for a secondary infection control. Our results showed that these four parameters are strongly influenced by the route of infection. For example, the dissemination from the local site of infection to the systemic organs is dependent on the amount and the rapidity of bacteria that enter in blood at the same time. The protective immune response after a primary and secondary infections seems dependent on the localization of bacteria (inter- or extra-cellular), the amount of bacteria, and the infected organs. The control of secondary i.p. infection in spleen requires B cells and CD4 T cells, while CD4 T cells or CD8 T cells are sufficient to control a secondary i.n. infection in the same organ. Finally, we showed that virB, a virulence gene defined as essential in in vitro Brucella model, can be partially dispensable, or even deleterious after i.p or i.d. infections, respectively. The intranasal model mimics one of the most physiological route of infection. Thus, we chose to deeply study this model. Following intra-nasal infection, the alveolar macrophages are the main (> 95 %) infected cells during the first 48 hours post infection. We used a without a priori approach (RNA sequencing) in order to find new potential genes involved in the early response in alveolar macrophages after Brucella infection. Among the 466 genes upregulated in alveolar macrophages, Acod1 was one of the most interesting candidate. Indeed, itaconate, a Krebs cycle derivate, produced by aconitate decarboxylase1 gene (Acod1, also known as Irg1), is emerging as a potential immunoregulatory metabolite since few years. This compound, produced mainly 4 in mitochondria of myeloid cells, is known to have two main roles: an anti-inflammatory one and an anti-bacterial one. In our model of intranasal Brucella infection, we observed that the deficiency of Acod1 does not trigger any inflammation signs in comparison to wild type mice. In contrast, we observed that itaconate inhibits the in vitro Brucella growth and that Acod1 deficiency increase the number of bacteria in the lungs of infected mice. These effects seem Brucella isocitrate lyase-dependent in both conditions. The understanding of how itaconate impacts the growth of Brucella could allow the development of new therapeutic drug against brucellosis.

la date de réponse	2020
langue originale	Anglais
L'institution diplômante	Universite de Namur
Sponsors	FRS-FNRS-Télévie & Fund for Research Training in Industry and Agriculture (FRIA)
Superviseur	Xavier De Bolle (Promoteur), Eric MURAILLE (Copromoteur), Thierry Arnould (Président), Jean-Pierre Gorvel (Jury), Laurence Van Melderen (Jury), Marta Romano (Jury) & Stanislas Goriely (Jury)