Upregulation of MHC-II (HLA-DR), CD40, and CD80 on neutrophils requires antigen and antigen-specific memory CD4⁺T cells. Representative histograms show the surface expression levels of HLA-DR (MHC II) (A,E) and the maturation markers CD40 (B) and CD80 (C) on neutrophils cultured for 30 hours alone or with autologous CD4⁺ T cells for all the indicated conditions. (D) Bar graphs show geometric mean fluorescence intensity (MFI) values of HLA-DR (mean ± SEM, n = 4 donors). (F) Proliferation of allogeneic naive T cells in a mixed lymphocyte reaction induced by neutrophils or monocytes. One representative donor of 3 is shown. (G) IFN-γ/IL-2/TNF production in responding pp65-specific CD4⁺ T cells stimulated by neutrophils or CD14⁺ monocytes. One representative donor of 3 is shown. (H) Bar graphs show the surface expression levels of HLA-DR, CD40, and CD80 on neutrophils after stimulation for 30 hours with supernatants (Sup) collected from culture of T cells only (Medium), T cells activated with anti-CD2/CD3/CD28 beads (Beads), or from the neutrophil–T-cell cocultures prepared as for the Ag presentation assay (Ag pres) (mean ± SEM, n = 4). *P< .05, **P < .01, ***P < .001, ****P < .0001. Unstim, unstimulated.