Effect of soluble fibrin on monocyte adherence to tumor cells. Calcein AM labeled PBM incubated with A375 cells after pre-treatment of A375 and/or PBM with RPMI or sFn prior to assay. sFn pre-treatment of tumor cells significantly increased adherence to untreated A375 cells compared to the untreated control (P < 0.01: n = 3). Preincubation of monocytes also marginally increased adherence to untreated A375 cells (P < 0.05: n = 3) compared to the untreated control, but to a significantly lower degree than with sFn treated A375 cells (P < 0.01 compared to monocyte sFn). sFn pre-treatment of both effector and target cells resulted in a significant inhibition of adherence (P < 0.05: n = 3) compared to the untreated control.