Tyrosine phosphorylation of STAT4 in response to IL-12. PBMCs obtained from a healthy control subject (lanes 1-2) and 3 months after transplantation from 2 patients with lymphoma (lanes 3-6) were incubated with or without IL-12 100 U/mL for 1 hour as indicated, lysed, resolved by SDS-PAGE, transferred to nitrocellulose membranes, and immunoblotted using antibodies specific for tyrosine phosphorylated STAT4, total STAT4, or GAPDH as indicated. Location of the specific band for total STAT4 is indicated by the arrow. The identity of the STAT4 band was confirmed as described in “Patients, materials, and methods.” Results are representative of those seen with 6 control samples and 6 patient samples that were tested.