Fig 1: Monocyte-platelet adhesion synapse formation drives antigen-specific immunity.(A) Top: Confocal imaging of purified human monocytes cultured with platelets overnight. Activated CD61+ (green) platelets are shown forming CD62p+ (yellow) and PSGL1+-mediated junctions (blue) with CD14+ (red) monocytes. Bottom: 3D reconstruction demonstrates punctate monocyte PSGL1 clustering around platelet CD62p. Scale bars, 5.30 µm. (B) Schematic of human experimental setup with soluble antigen (Ag). Platelet-containing (PBMC+pl+) and platelet-depleted (PBMC+pl-) PBMCs were prepared from healthy human donors. PBMC groups were incubated overnight with soluble tumor antigens, melanoma-associated antigen recognized by T cells long peptide (MART1 LP) or E7 LP, followed by washing and 3-day coculture with antigen-specific transgenic human T cells, DMF5 or E7, respectively. Supernatants were analyzed at end of culture (day 4). (C to E) Human IFNg (hIFNg) ELISA of (C) DMF5 cultured with PBMC+pl+ or PBMC+pl- pulsed with MART1 LP at varying concentrations, (D) DMF5 cultured with MART1 LP–pulsed PBMC (left) or monocytes (right) with or without platelets or recombinant human P-selectin stimulation, and (E) E7 T cells cultured with E7 LP–pulsed PBMC+pl+ or PBMC+pl- or E7 T cells only (PBMC-). (F) FACS quantitation of CD86, HLA-DR, HLA-A,B,C, and CD14 in donor PBMCs at throughout incubation (n = 5 to 7). All values are means ± SD of at least three independent experiments. (C to E) One-way ANOVA and (F) two-way ANOVA, ****P < 0.0001, **P < 0.01, *P < 0.05. (F) Each point represents data from an individual healthy blood donor.