Resistin directly inhibits bacterial killing in neutrophils

Sepsis-induced immunosuppression is a key factor contributing to the morbidity and mortality of critically ill patients, and polymorphonuclear neutrophil dysfunction is believed to be a hallmark of this immunosuppression. Circulating myeloid cells produce the cytokine resistin (RETN), which has been associated with poor outcomes in sepsis/septic shock and can directly inhibit neutrophil function. We previously demonstrated that resistin caused a dose-dependent impairment in neutrophil migration, reactive oxygen species production, and bacterial clearance in neutrophil cell lines. However, the relative antimicrobial responses of other innate immune cells to Gram-positive and Gram-negative infections in the presence of elevated levels of resistin have not been evaluated. We hypothesized that resistin directly contributes to sepsis-induced immunosuppression by selectively targeting the neutrophil component of the innate cellular immune system. Thus, the goal of the present study was to compare the effect of resistin on bacterial killing using monocultures or co-cultures of monocyte and neutrophil cell lines, as well as to extend our findings to primary immune cells.

Our results indicate that human resistin impairs the ability of neutrophils to kill the Gram-negative bacterium Pseudomonas aeruginosa and the Gram-positive bacterium Staphylococcus aureus. In contrast, with the exception of macrophages incubated with P. aeruginosa, resistin did not affect the ability of macrophages or monocytes to kill either Gram-positive or Gram-negative organisms. Furthermore, co-incubation of neutrophils with increasing proportions of monocytes did not enhance bacterial killing. Resistin blocked bactericidal activity through partial reduction of F-actin polymerization and suppression of the oxidative burst in neutrophils.

Our studies indicate that resistin selectively impairs neutrophil bacterial killing. These findings further support the notion that resistin can mimic cell type-dependent immunosuppressive effects. This is consistent with its putative role in the pathogenesis of bacterial sepsis.