Differences between infiltration of mononuclear-macrophages and neutrophils during Leptospira interrogans infection and underlying mechanisms
Objective 
To understand the differences between infiltration of mononuclear-macrophages and neutrophils during Leptospira interrogans (L.interrogans) infection and the underlying mechanisms. 
 
 
Methods 
Histological changes in mouse lung, liver and kidney tissues were detected using hematoxylin and eosin (HE) staining following infection of C3H/HeJ mice with L.interrogans serovar Lai strain 56601. Infiltration of peripheral blood-derived CD11b+ mononuclear-macrophages and Ly6G+ neutrophils in lung, liver and kidney tissues collected form L.interrogans-infected C3H/HeJ mice was detected with immunohistochemistry. Levels of mononuclear-macrophage chemokines and neutrophil chemokines in serum samples of L.interrogans-infected mice were detected with chemokine detection microarray. 
 
 
Results 
Lung, liver and kidney tissue samples collected from L.interrogans-infected C3H/HeJ mice presented typical histopathological changes of leptospirosis, such as inflammatory cell infiltration in these tissues, pulmonary hemorrhage, extensive hepatocyte necrosis and serious nephrohemia. Results of immunohistochemical staining showed that a large number of peripheral blood-derived CD11b+ mononuclear-macrophages were presented in lung, liver and kidney tissues of L.interrogans-infected mice, but few neutrophils could be found in these tissues. The mouse chemokine detection microarray confirmed that the levels of mononuclear-macrophage chemokines (I-309, MCP-1, MCP-5, MIP-1α and RANTES) in serum samples of L.interrogans-infected C3H/HeJ mice were significantly increased during infection (P 0.05). 
 
 
Conclusion 
Mononuclear-macrophages rather than neutrophils are the major infiltrating phagocytes during L.interrogans infection and play a crucial role in the elimination of Leptospira invasion. 
 
 
Key words: 
Leptospira interrogans; Mononuclear-macrophage; Neutrophil; Infiltration; Chemokine