[Pattern recognition and activation effect of mast cells in vitro infected by Brucella suis S2].

Objective: To study the pattern recognition and activation effect of mast cells infected by Brucella (B.) suis S2.

Methods: Mast cells derived from bone marrow in vitro were infected by B.suis S2. The change in the cell morphology was observed with Wrights-Giemsa's staining, and cell degranulation was tested with toluidine blue staining. The extracellular levels of histamine, IFN-γ and IL-12 of mast cells at 1 and 12 h after infection were detected by indirect ELISA. The uptake pattern of mast cells to B.suis S2 was determined by laser-scanning confocal microscopy. The expressions of TLR4 and TLR8 mRNA were detected by RT-PCR at 12 and 24 h after infection by B.suis S2, and the TLR4 and TLR8 protein expressions were detected by flow cytometry at 24 h.

Results: The form of mast cells infected by B.suis S2 was obviously changed. Significant degranulation was observed at 1 h, and at 1, 12 h post-infection by B.suis S2, the content of histamine secreted by mast cells was significantly higher than that of normal control group (P<0.05), and IFN-γ and IL-12 were not found. At 30 min and 1 h, B.suis S2 bound to the mast cell surface and were not uptaken into the mast cells. Compared with the control group, the expression of TLR4 mRNA increased after 12 h infection by B.suis S2, and was reduced at 24 h. The expression of TLR4 protein rose at 24 h, but the expression of TLR8 mRNA and protein did not alter at 12 and 24 h after infection by B.suis S2.

Conclusion: B.suis S2 can bind to the cell surface and activate mast cells, cause their degranulation, induce the release of histamine, but IFN-γ and IL-12 were not found during the observing time. The mechanism may be that B.suis S2 can be recognized by mast cells through TLR4 but can not be phagocytosed by mast cells.