Altered pulmonary capillary permeability in immunosuppressed guinea pig infected with serum type 1 Legionella pneumophila

Abstract

Background: In immunosuppressed hosts, Legionella pneumophila (Lp) infection usually develops into severe pneumonia, which is pathologically characterized by increased vascular permeability and pulmonary edema. At present, the changes in pulmonary capillary permeability (PCP) and the formation and development of pulmonary edema in Lp-infected immunosuppressed hosts and the associated mechanisms are unclear. Methods: we established an animal model of normal and immunosuppressed guinea pigs infected by Lp. The isolated perfused lung system was used to investigate the degree of PCP changes. Pathological and immunofluorescence tests were performed to explore the mechanism underlying these PCP changes. Result: The result indicated that PCP was most significantly increased in the immunosuppressed Lp-infected group, and repeated analysis of variance showed that the infectious and immunosuppressive factors acted synergistically (P = 0.0444). Hematoxylin–eosin staining and electron microscopy revealed more-severe morphological damage in the lung tissues and pulmonary capillaries of the immunosuppressed Lp-infected animals than in the animals with Lp infection alone. An immunofluorescence analysis showed that immunosuppression reduced the expression of the vascular endothelial cell junction protein VE-cadherin (P = 0.027). VE-cadherin was significantly lower in the immunosuppressed Lp-infected group than in the Lp-infected only group (P = 0.001). Conclusion: The present study suggested that Immunosuppression combined with Lp infection causes more-severe damage to pulmonary capillaries than Lp infection alone, significantly increasing PCP.