A role for CD9 in the formation of antigen-dependent monocyte/T-cell conjugates. CMFDA-labeled monocytes loaded or not with SEE were incubated for various periods of time with CMTMR-labeled Jurkat cells before flow cytometry. (A) Conjugate formation at t = 0 minute and t = 40 minutes of incubation between monocytes loaded with 10 μg/mL of SEE and Jurkat cells are detected as CMFDA⁺ CMTMR⁺ events. (B) Kinetic analysis of conjugate formation between CMFDA-labeled monocytes loaded or not with SEE (10 μg/mL) and CMTMR-labeled Jurkat cells. (C) CMFDA-labeled monocytes loaded or not with SEE (10 μg/mL) were incubated with CD9 (PHN200), CD38 (IB4), anti–HLA-DR (D1.12), CD11A (HI-111), or isotype control mAbs (5 μg/mL) before conjugate formation with Jurkat cells. The percent of SEE-specific conjugates are indicated for different times. (D) Formation of conjugates was analyzed for different concentrations of SEE and different concentrations of CD9 mAbs.