Administration of nonviral gene vector encoding rat [beta]-defensin-2 ameliorates chronic Pseudomonas aeruginosa lung infection in rats

Background Beta-defensin-2 (BD-2) plays an important role in host defense against pathogenic microbe challenge by its direct antimicrobial activity and immunomodulatory functions. The present study aimed to determine whether genetic up-regulation of rat BD-2 (rBD-2) could ameliorate chronic Pseudomonas aeruginosa lung infection in rats. Methods Plasmid-encoding rBD-2 was delivered to lungs in vivo using linear polyethylenimine at 48 h before challenging with seaweed alginate beads containing P. aeruginosa. Macroscopic and histopathological changes of the lungs, bacterial loads, inflammatory infiltration, and the levels of cytokines/chemokines [interleukin (IL)-1[beta], tumor necrosis factor (TNF)-[alpha], kertinocyte-derived chemokine (KC), macrophage inflammatory protein-2 (MIP-2)] were measured at 3 and 7 days post-infection (p.i.). Results The overexpression of rBD-2 resulted in a significant increase in animal survival rate (at 3 days p.i.), a significant decrease in bacterial loads in the lungs (at 3 and 7 days p.i.), and significantly milder lung pathology. In addition, the overexpression of rBD-2 led to increased infiltration of polymorphonuclear neutrophils (PMN), and elevated protein expression of cytokines/chemokines (IL-1[beta], TNF-[alpha], KC and MIP-2) at the early stage of infection (at 3 days p.i.), at the same time as being dramatically decreased at the later stage of infection (at 7 days p.i.). Conclusions Genetic up-regulation of rBD-2 increased animal survival rate, and reduced bacterial loads in lungs after bacterial infection. The overexpression of rBD-2 also modulated the production of several cytokines/chemokines and increased PMN recruitment at the early stage of infection. Our findings indicate that the enhancement of BD-2 may be an efficacious intervention for chronic P. aeruginosa lung infection. Copyright © 2010 John Wiley & Sons, Ltd.