Fixed monocytes promote CD40L expression. Monocytes, or monocytes that had been fixed and washed, were reconstituted with autologous elutriated lymphocytes. Cells were plated at the same density as in unfractionated PBMCs and stimulated with anti-TCR mAb. Autologous PBMCs were cultured in parallel. Cells were harvested at 6 hours and stained for CD40L expression. Data are mean ± SE of 3 donors.