Brucella cyclic glucans and the induction of the inflammatory response

MARA S. ROSET , JUAN M. SPERA AND GABRIEL BRIONES

Conferencia; Brucellosis 2011, International Research Conference; 2011

Brucellosis is a worldwide zoonosis caused by the bacterial pathogen Brucella. In ungulates (cows, goats pigs and sheeps) abortions, placentitis, epididymitis and orchitis are the most common symptoms associated to the disease. In humans, brucellosis begins as an acute febrile illness characterized by flu-like symptoms with fever, myalgia, and malaise. At the acute phase, antibiotic treatment efficiently controls the infection and patients fully recovered from brucellosis. If the disease is misdiagnosed or asymptomatic, brucellosis can evolve to a chronic phase where patients become chronically ill with periodic relapses that include undulant fever, arthritis, meningitis, and endocarditis. Since inflammation is an important outcome of Brucella persistent infection, characterization of PAMPs (pathogen-associated molecular patterns pattern) in Brucella (recognized by the innate immune) becomes important to understand the interaction between Brucella and its host. Although Brucella lipoproteins have been shown to elicit a TLR2-mediated inflammatory response, Brucella LPS and flagellin are poor inducers of the innate immunity suggesting that during coevolution with its host Brucella  have downregulated the total number of PAMPs to avoid an extensive recognition by pattern recognition receptors (PRR) that might be detrimental to the bacterial-host interaction. Here we explore Brucella cyclic â1-2 glucans (CGs) as elicitors of the inflammatory response. CGs are polysaccharides synthesized by a membrane bound protein encoded by cgs gene and mutants in CG synthesis are attenuated in virulence in the mouse model. When infecting mice with Brucella abortus wild type or cgs mutant we observed: although the numbers of bacteria recovered from spleens at two weeks postinfection were similar in both strains, the average spleen weight observed in wild type strain was four times higher than the observed in cgs mutant infected mice. Firstly we tested if the absence of CG affects indirectly the expression of other PAMPs by quantification of relative amounts of LPS and lipoproteins (Omp19 and Omp25) by western blot analysis and no difference was observed between both strains. To explore a direct role of CG in the inflammatory response we performed mouse experiments supplementing cgs mutant with purified CG, added to infection inoculums and  by daily injection (intraperitonealy) of CG during the first week postinfection and no complementation in splenomegaly was observed. To characterize in more detail the differential inflammatory responses observed, we analyzed the total number of splenocytes, quantified the number of B and T cells by immunofluorescence and FACS and compared profiles of cytokines obtained from splenocytes derived from cgs and wild type infected animals.