132 Chapter 4 the T cell subset composition was altered from the second week after injury, indicative of an adaptive immune response [56]. To study the phenotype of circulatory T cells in burn patients, we analyzed CCR4 and CCR6 expression and found increased numbers of CCR4+CCR6+ CD4+ T cells, which might indicate a shift toward a Th17 T cell phenotype. This notion was supported by increased levels of MIP-3α, a natural ligand of CCR6 [57], from PBD 12 onward, as well as high levels of IL-6, TGF-β1, and TGF-β2, which in combination can induce a Th17 response [18,58]. Additionally, we observed increased numbers of CCR4+CCR6¯ CD4+ T cells, indicative of a Th2 phenotype [59]. This was associated with an increase in IL-13, a Th2 cytokine [60], at PBD 12–21. Animal experiments have also shown that burn injury induces a mixed Th2/Th17 response. Moreover, IL-17 which is released by Th-17 cells is involved in the recruitment and activation of neutrophil [18,61,62]. This might explain the high neutrophil counts that peak during PBD 16–21. Burn injury was also associated with an increase of Tregs, which are likely part of the immune system’s attempt to resolve the acute inflammation [63]. Upon in vitro culture, Treg from severely burned patients produced elevated levels of IL-10 in the first 21 days after injury [64]. Here, plasma levels of IL-10 were only increased at PBD 0–3. An early increase of serum IL-10 was also found in severely burned children, which was followed by a small, nonsignificant elevation of circulatory IL-10 afterward [5,65,66]. This suggests that in vivo, the suppressive response from Tregs might be impaired after PBD 3, possibly due to the high levels of pro-inflammatory cytokines and number of acute phase immune cells. In addition, we found evidence for Treg differentiation, as both CCR6+ and CCR6¯ Tregs were present. This suggests that there is a burn-induced mixed phenotype within the Treg population [57,67]. The transformation of Tregs into putative pathophysiologic Tregs has been proposed before [68,69] and, in this case, could be caused by burn-induced DAMPs and pro-inflammatory mediators such as the CCR6 ligand MIP-3α. Although functional assays are needed to verify the phenotype of these Tregs, our data suggest that severe burn injury causes a shift in the T cell subsets toward more pro-inflammatory subtypes, tipping the balance and thereby continuing the inflammation. The increase in inflammatory mediators is indicative of a persistent systemic inflammatory immune response due to severe burns. However, all included burn patients were at high risk for infection, such as central line-associated bloodstream infection. These infections were not observed in this study but bacterial presence could have influenced the levels of inflammatory mediators. Medication could have affected the immune response, but all patients were treated in a similar manner, involving the administration of antibiotics and analgesics. Although the differences in immune components in the blood between burn wound patients and healthy controls were significant and remained increased over time, the sample size is a limitation of our study. Missing data was caused by less frequent blood withdrawal at the infirmary, delayed start
RkJQdWJsaXNoZXIy MTk4NDMw