Sera from each of the 16 patients with PsA and of the 15 controls were incubated with elutriated monocytes from a single healthy donor. Sera from patients and controls were obtained at baseline. Medications of patients at baseline are reported in Table 1. FCS was used as negative control. The experiments were performed twice, using cells from two different healthy donors; each experiment was carried out in triplicate wells. The data represent mean±SD (error bars). Comparison between means was performed by Student's unpaired t test. MFI values of ILT4 expression in CD40L-stimulated and, in parenthesis, unstimulated cells were as follows: FCS-exposed, 145±13.9 (34.5±12.4); normal serum-exposed, 120.3±11.2 (30.9±13.7); patient's serum-exposed 33.6±8.4 (36.1±14.6). CD40L: FCS-exposed vs. normal serum-exposed, P>0.05; normal serum-exposed vs. patient's serum-exposed, P<0.001. Unstimulated: FCS-exposed vs. normal serum-exposed, and normal serum-exposed vs. patient's serum-exposed, P>0.05.