Experimental exposure of crude culture filtrate upregulates PD-1 on T lymphocytes.

is the causative agent for melioidosis. Because of its intracellular nature, the bacterium is capable of replicating within a plethora of eukaryotic cell lines. can remain dormant within host cells without symptoms for years, causing recrudescent infections. Here, we investigated the pathogenesis mechanism behind the suppression of T cell responses by . Peripheral blood mononuclear cells (1×10 cells/well) isolated by Ficoll Paque (Sigma-Aldrich) density gradient centrifugation were incubated with optimized concentrations of bacterial crude culture filtrate antigens (CFAs) (10 ug ml) and heat-killed bacteria [1 : 10 multiplicity of infection (m.o.i.)]. Following incubation, cells were investigated for surface expression of coinhibitory molecules by flow cytometry. We found that induced the upregulation of programmed death 1 (PD-1), a molecule responsible for T cell exhaustion, on T cells following exposure to crude CFAs of . This upregulation of PD-1 probably contributes to poor immune surveillance and disease pathogenesis.