O15 - Mitigation of Splenocyte Apoptosis by Th2-Polarized Invariant Natural Killer T Cells Reduces Disease Severity in Intra-abdominal Sepsis

Background: Invariant natural killer T (iNKT) cells are potent lymphocytes that can produce pro- and/or anti-inflammatory cytokines early in the course of an immune response. They present an attractive target for therapy in a wide range of human diseases. Because little is known about their role in sepsis, we sought to determine the frequency of iNKT cells in septic patients. We also employed a mouse model of intra-abdominal sepsis (IAS) to test the effect of OCH, a Th2-polarizing agonist of iNKT cells that induces an anti-inflammatory phenotype, on disease severity.

Hypothesis: We hypothesized that the frequency of iNKT cells would be elevated in septic patients, and that treatment with OCH would ameliorate disease severity in mice with IAS.

Methods: Blood samples were drawn from patients with or without sepsis admitted to the intensive care unit within 48 hours. The frequencies of CD3+ conventional T cells and CD3+CD1d tetramer+ iNKT cells were determined by flow cytometry. A fecal solution was administered intraperitoneally to either OCH- or vehicle-treated C57BL/6 (B6) mice to induce IAS. After 24 hours, lymphocyte subsets (T cells and iNKT cells) were evaluated within the liver and spleen by flow cytometry. Organs were also harvested for histological and cytokine analyses.

Results: Twenty-three septic and seven non-septic poly-trauma patients were identified. Peripheral blood iNKT cell frequency was higher (p= 0.047) in patients with sepsis (0.086% of T cells) compared to non-septic poly-trauma patients (0.014% of T cells). OCH-treated mice with IAS had significantly lower sepsis severity scores (p< 0.0001) and prolonged survival compared to vehicle-treated mice (p= 0.015). Treatment with OCH markedly reduced apoptosis of splenic macrophages, T cells, and B cells, but not natural killer (NK) cells. The expression of pro-inflammatory cytokines was also significantly reduced within the spleens of OCH-treated mice.

Conclusions: Septic patients have an increased proportion of iNKT cells compared to non-septic patients. Polarizing iNKT cells towards a Th2 phenotype significantly reduces disease severity in IAS by mitigating splenocyte apoptosis, a novel finding that has not been previously reported. This study highlights iNKT cells as potentially important targets for therapy in sepsis.