Treatment with Fms‐like tyrosine kinase 3 ligand reverses lung dendritic cell immunoparalysis and ameliorates zymosan‐induced secondary lung injury in mice
Depletion and dysfunction of dendritic cells in the lung can induce local immunoparalysis, which often leads to multiple organ dysfunction syndrome (MODS)‐associated mortality. A therapeutic strategy that reverses this immunoparalysis is required. In the present study, we examined the effects of in vivo Fms‐like tyrosine kinase 3 ligand (Flt3L) treatment on zymosan (zym)‐induced secondary lung injury and dendritic cell (DC) immunoparalysis. BALBc mice were divided randomly into four groups (20/group): (1) sham [intraperitoneal (i.p.) saline] + vehicle [subcutaneous (s.c.) 0·01% mouse serum albumin]; (2) sham + Flt3L (s.c.); (3) zym (i.p.) + vehicle; and (4) zym + Flt3L. Injections were for 9 consecutive days; 12 days later we examined: survival rate (monitored for 12 days); lung tissue histopathology (haematoxylin and eosin staining); plasma indices of lung function (pH, PaO2, PaCO2, HCO3–); DC subsets in lung tissue; and lung DCs production of interleukin (IL)‐12p70 and IL‐10. Zym administration resulted in increased mortality associated with significant lung histopathological changes and abnormal blood gas indices; however, these pathological changes were ameliorated by Flt3L treatment. Zym injections also resulted in significant reductions in DC subsets recovered from lungs [CD11c+major histocompatibility complex (MHC)‐II/I‐Ad+, CD11c+CD11b+ and CD11c+B220+]. Importantly, in‐vivo Flt3L treatment reversed these trends for DC immunoparalysis by increasing the percentages of recovered DC subsets concomitant with increased DC production of IL‐12 p70 and decreased IL‐10 production. These results suggest that Flt3L may have therapeutic potential for reversing DC immunoparalysis and ameliorating lung injury secondary to MODS.