Decreased neutrophil surface expression of CXCR1 and CXCR2 during engraftment. (A) Representative flow plots from a healthy control, a HSCT recipient during engraftment, and an HSCT recipient around day +100. Cells were gated as CD11b(+) neutrophils. Flow plots are shown with CXCR1 on the y-axis and CXCR2 on the x-axis. Coexpression of CXCR1 and CXCR2 is similar between the healthy control sample and HSCT recipient at day +100, but surface expression of both is decreased during engraftment. (B) The % of CD11b-positive neutrophils with coexpression of CXCR1 and CXCR2. CXCR1 and CXCR2 surface expression were compared during engraftment (N = 6), day +100 (N = 4), and in healthy controls (N = 5). There is no difference seen between the surface expression of CXCR1 and CXCR2 in HSCT recipients at day +100 and healthy controls, but the surface expression of both is significantly lower in HSCT recipients during engraftment when compared with HSCT recipients at day +100 and healthy controls (P = .0095 and P = .0043, respectively).