Brucellosis 2003 proceedings - PHIDIAS

Short Oral Communications
Immunology, pathogenesis and host-pathogen interaction
PO1- HUMAN-Brucella INTERACTIONS: SPECIES SPECIFIC PERSPECTIVES.
A. Mathison, L. Eskra, G. Splitter. University of Wisconsin, Madison, USA.
A dynamic relationship exists between the human host and the bacterial
pathogen during Brucellosis infection. Eukaryotic gene expression has an influential
role in the clearance or persistence of various Brucella species within the host. An in
vitro infection model was used to observe differential gene expression of the
macrophage when infected with two different species of Brucella. Brucella species
were chosen based on their dissimilar abilities to infect humans in nature. Human
infections with Brucella melitensis 16M are severe in pathogenesis and human cases
of infection have been widely reported; conversely, Brucella ovis has not been
reported to cause human infection and pathogenesis is, at most, limited.
Differentiated U937 macrophages infected over time with B. melitensis 16M and B.
ovis exhibits divergent patterns of bacterial persistence and clearance, respectively.
The bacterial clearance or persistence may, in part, be influenced by host
macrophage genes that are differentially expressed when macrophages are
combating Brucella infection. Observing the differentially expressed genes correlated
to human persistence and clearance of B. melitensis and B. ovis, respectively, will
provide insight into cellular mechanisms involved in the innate immune defense.
These identified mechanisms could become molecular targets to improve host
clearance of and protection against Brucella infection.
PO2- SUBVERSION AND UTILIZATION OF THE HOST CELL CYCLIC
ADENOSINE 5’-MONOPHOSPHATE/PROTEIN KINASE A PATHWAY BY Brucella
DURING MACROPHAGE INFECTION.
Gross A., Liautard J-P and Dornand J. INSERM U431, Montpellier, France.
Brucella spp are intramacrophage pathogens. Therefore, the macrophage
response to infection has important consequences for both, the survival of
phagocytozed bacteria and the further development of host immunity. Very little is
known about the macrophage cell signaling pathways initiated upon infection and the
virulence strategy that Brucella use to counteract these responses and secure their
survival. In a previous study, we have shown that macrophages activated by
SR141716A, a ligand of the cannabinoid receptor CB1, acquired the capacity to
control Brucella. We observed that the CB1 receptor-triggering engages the
microbicidal activity of phagocytes. As CB1 receptor belongs to the family of G-
protein-linked receptors, we explored the cAMP signaling pathway. We showed that
SR141716A activity implicate this pathway. Taking advantage of this result, we then
demonstrated that Brucella infection elicited a stimulation of the cAMP pathway
which resulted in prolonged activation of PKA and phosphorylation of the
transcription factor CREB. Using specific inhibitor of the PKA pathway, we
demonstrated that the activation of the cAMP/PKA pathway was crucial for the
survival of Brucella within macrophages. Furthermore kinetics experiments which
these inhibitors showed that the establishment of the bacteria at the early steps of
infection required PKA activation. Preliminary results obtained with endosomal
markers, suggested that the formation and nature of the phagosomal compartments
in which Brucella resides are highly dependent of the activation of the cAMP/PKA
pathway. We thus characterized, a primordial virulence strategy of Brucella involving
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Brucellosis 2003 International Research Conference