Involvement of integrins in endoglin-dependent cell adhesion. (A-F) Light microscopy analysis of adherent cells. Plates were coated with BSA (A), endoglin (B) or CXCL12 plus endoglin (C-F). Nalm6 cells were incubated for 1 hour at 37°C in the absence (A-B) or in the presence of the inhibitory anti-β1 integrins mAb LIA1/2 (D), the activator anti-β1 integrins mAb TS2/16 (E) or soluble endoglin (F). Bound cells were visualized by inverse light microscopy. Magnification, ×200. (G-J) Quantification analysis. Plates were coated with BSA, endoglin, CXCL12, or endoglin plus CXCL12, as indicated. Bound Nalm6 cells, previously labeled with CFSE, from the same experiment in panels A through F were lysed and quantification was carried out (G). A representative binding experiment with K562 cells is also shown (H). (I-J) Role of anti-endoglin antibodies in cell adhesion assays. Nalm6 (I) and K562 (J) cells were labeled with CFSE, loaded in the wells and incubated with or without mAb P4A4 (anti-endoglin), mAb HC1/6 (anti-CD31), or an irrelevant IgG2b mAb (control matched), as indicated for 1 hour at 37°C. Bound cells were lysed and quantification was carried out using a fluorescent analyzer. Results are shown as percentage respect to total input (100%). Each assay was performed in triplicate and the SEM is indicated. **P < .005; *P < .01. CXC indicates CXCL12; LIA, mAb LIA1/2; TS2, mAb TS2/16; S.Eng, soluble endoglin; HC1, mAb HC1/6; and IgG, IgG2b.