Arginase expression by interphase neutrophils. (A) T cell proliferation in longitudinal (day 0, 2, 3, and 7) samples from a representative severe sepsis patient. At each time point, T cell responses were measured in total interphase cells (grey fill), with addition of an arginase inhibitor (black hashed line), and after CD66b + interphase neutrophil depletion (black solid line). Only on day 2 and 3, removal of interphase neutrophils- enhanced proliferation. On day 2, addition of the arginase inhibitor also increased proliferation. No increased proliferation was observed on day 0 and 7 following depletion of interphase neutrophils, suggesting the interphase neutrophils were inactive. Control interphase cells in the absence of stimulation are designated by the dotted line. (B) In the same severe sepsis patient, mRNA was extracted from total interphase cells and the enriched interphase neutrophils at all longitudinal (day 0, 2, 3, and 7) time points. The line graph shows the fold change in arginase 2 mRNA expression in total cells (filled circles) and the interphase neutrophils (open circles) relative to interphase cells (PBMC) from a healthy control. (C) In the same severe sepsis patient, arginase 1 mRNA expression was evaluated at each time point in total interphase cells and the enriched interphase neutrophils. Arginase 1 expression was only detected on day 3 in both total interphase cells and the interphase neutrophils.