PDCD1 and Sepsis: In contrast to immune suppression during established sepsis, wherein PD-1/PD-L1 interactions between antigen-presenting cells and T cells are shown to strongly influence immune hyporesponsiveness [52–54], anti-PD-1 antibody treatment did not influence LPS- or CpGA DNA-induced tolerance or cross-tolerance in the splenocyte model (Fig 6).