Reliminary Study On The Interaction Between Macrophages And Haemophilus Parasuis

Haemophilus parasuis is a commom bacterium which clones on the upper respiratory tract of pigs, to cause Glasser's disease on the in appropriate conditions. The disease is characterized by meningitis, polyarthritis, fibrinous polyserositis and pneumonia. It is reported that the pathogeny cloning in the nose invades lung of the host from bronchus, then causes to pathological damage and clinical symptom through blood circulation. Neuraminidase named sialidase which is a kind of endotoxin could be examined in the plasma of illness pigs, and destroys the immunologic barrier of hosts by two main ways of exposing the receptors of pathogeny through removing sialic acid on the surface of host and descreasing the viscosity of mucoprotein, but the molecular mechanisms is unknown..We compared the phagocytosis susceptibility between virulent strains (Nagasaki and 0165 of serovar 5) and low virulent strains (SW114 of serovar 3 and 4-11 of serovar 11) of Haemophilus parasuis using mouse monocyte macrophages (RAW264.7) as a cell model. The experiment indicates virulent strains are more sensitive on the capability of antiphagocytosis than low virulent strains based on mouse monocyte macrophage. The results were agree with the previous report based on the primary porcine alveolar macrophage(PAM) model. In the experiments of phagocytosis inhibition assay, bacterial survival tests after phagocytosis, the results based on the mouse monocyte macrophage were also similar with those based on the porcine alveolar macrophages. These suggested that the RAW264.7 cell line could be used to study the interaction between H. parasuis and macrophages replace the primary PAM cells.Based on the RAW264.7 cell model, the decrease of mitochondrial membrane potential(△Ψm) and DNA fragmentation were detected respectively to study the differences of capability to induce apoptosis between virulent strains and low virulent strains. Virulent strains, Nagasika induced apoptosis more quickly than low virulent strains in the early stage of apoptosis. Differently from other pathogens on the mechanism of immune system damage, some apoptosis output which H. parasuis strains produced would inhibite production of pro-inflammatory cytokines in the process of apoptosis, lighten inflammatory reaction and avoid to be cleared by immune system of the host. In this study, RAW264.7 cells were stimulated with heat killed or polymyxin B (PmB) treated H. parasuis, then the production of IL-6 and IL-8 in the different time post stimulation were detected. The results showed the levels of IL-8 secreted by the stimulated RAW264.7 cell significantly decreased.