Abstract:

Objective To investigate the effect of Mycoplasma pneumoniae community-acquired respiratory distress syndrome (CARDS) toxin on peripheral blood mononuclear cell subsets in mice. Methods The recombinant CARDS toxin was prepared. Thirty-two mice were divided into the model group and the normal control group according to random number table with 16 mice in each group. Each mouse in the model group was injected with 40 μL PBS containing 50 μg of CARDS toxin. In the normal control group, the same dose of PBS was injected into trachea. Blood samples were collected from abdominal aorta 24 h after the modeling, and the proportion of peripheral monocyte subsets (CD11b⁺Ly6G^-Ly6C⁺) was detected by flow cytometry. The mice were sacrificed, and lung histopathological changes were observed by HE staining, and the lung tissue injury score was performed. The expression levels of interleukin (IL)-1β and IL-18 in lung tissue were detected by Real-time PCR. The levels of IL-1β and IL-18 in peripheral blood were determined by enzyme-linked immunosorbent assay. Results Compared with the normal control group, CD11b⁺Ly6G^-Ly6C⁺ ratio of mouse monocytes was increased in the model group (P<0.05). HE staining showed that alveolar wall thickened, inflammatory cell infiltration increased, pathological score increased significantly (P<0.01), the expression levels of IL-1β and IL-18 mRNA in lung tissue and contents of inflammatory cytokines IL-1β and IL-18 in serum increased significantly (P<0.01). Conclusion The increased proportion of Ly6C⁺ monocytes in mice induced by CARDS toxin may be closely related to the incidence of Mycoplasma pneumoniae pneumonia.

Key words: pneumonia, Mycoplasma, toxins, biological, monocytes, interleukin-18, community-acquired respiratory distress syndrome