Fig. 5.

Human umbilical vein endothelial cells (HUVECs) express FcγRI (CD64). (a,b) HUVECs before and after incubation with fluorescein isothiocyanate (FITC)-conjugated mouse anti-human CD64 (FcγRI), clone 10.1 [immunoglobulin (Ig) G1]. Cells were counterstained with 4′,6-diamidino-2-phenylindole (DAPI). Cell surface CD64 appears as punctate staining. (c) Human peripheral blood mononuclear cells (PBMCs), i.e. lymphocytes (L) plus monocytes (M) adhering spontaneously to HUVECs following incubation for 18 h at 37°C. Cells were visualized using an inverted microscope at a magnification of ×400. Examples of adherent cells are indicated by arrows. (d) Increased binding of PBMCs to HUVECS (18 h at 37°C) as a result of preincubating the same number of cells (opsonization) with mouse anti-CD28 (clone 204.12). No increase in binding was observed when cells were preincubated at 4°C for 1 h with mouse IgG2a at the same concentration (4 µg per 10⁶ cells). Based on microscopic inspection of 100 HUVECs the ratio of PBMC : HUVEC was 1:1 for non-opsonized cells and 2:1 for anti-CD28 opsonized cells.