Intravenous calcitriol treatment benefits the homeostasis of CD4⁺ T cells and attenuates kidney injury in obese mice complicated with polymicrobial sepsis

Objectives: Sepsis is a lethal clinical condition with dysregulated cluster of differentiation (CD) 4+ T cells that leads to inflammation and multiorgan injury. Low vitamin D levels are commonly seen in patients with sepsis. Obesity is a state with oxidative stress and chronic inflammation. Both obesity and low vitamin D levels are associated with adverse outcomes in patients with sepsis. This study investigated the effects of calcitriol on CD4+ T-cell polarization and kidney injury during sepsis. Methods: Mice were fed a high-fat diet to induce obesity. One group of obese mice served as the control group and in the other two groups (SS and SD) were performed cecal ligation and puncture (CLP) to induce sepsis. Mice in the SS group were injected with saline and those in the SD group with calcitriol 1 h after CLP via tail vein. Mice with sepsis were euthanized at 12 h and 24 h after CLP, respectively. Results: Sepsis led to a decrease in circulating CD4+ T-cell percentage, and T helper (Th) 2, Th17, and regulatory T (Treg) cell percentages were upregulated. Compared with the SS group, the SD group maintained blood CD4+ T-cell levels, and were reduced the Th2 and Th17 percentages as well as the Th17:Treg ratio. Also, plasma levels of cathelicidin increased, but inflammatory chemokines and kidney injury markers were reduced. Higher arginase-1 and lower inducible nitric oxide synthase expressions in the SD group indicated M1 macrophage polarized toward the M2 type. Conclusions: These findings suggest that intravenous calcitriol administration after sepsis modulates the homeostasis of CD4+ T-cell subpopulations associated with alleviating sepsis-induced kidney injury in obese mice.