Lack of cytokine binding to the surface of PHA-T-cell blasts. PHA-T-cell blasts from a positive control (C+), a negative control (C-), and the patient (P) were incubated without (dotted line) or with (plain line) IL-12p70 or IL-23 for 30 minutes at 4°C. The PHA-T-cell blasts were then incubated with a purified mouse anti-IL-12 p40 antibody, followed by a biotinylated anti-mouse antibody, and antibody binding was detected by incubation with PE-conjugated streptavidin.