CIRCULATING INTERLEUKIN-2 RECEPTORS ARE A GROUP OF MULTIMERIC PROTEINS WITH IMMUNOREACTIVITY FOR INTERLEUKIN-2 RECEPTOR-ALPHA, RECEPTOR-BETA, AND RECEPTOR-GAMMA CHAINS

Soluble interleukin-2 receptor (sIL-2R) alpha chain serum levels as de termined by enzyme-linked immunosorbant assay (ELISA) are commonly use d to monitor various inflammatory and neoplastic disorders associated with lymphocytic proliferation and activation. The in vivo structure o f this soluble receptor species, however, is not characterized. We inv estigated sera with elevated sIL-2R serum levels of patients with hist ologically proven cutaneous T cell lymphoma (CTCL) and high-dose IL-2- treated melanoma patients and healthy donors. Purified recombinant IL- 2R alpha and beta chain molecules, produced by transfection of NIH/3T3 fibroblasts and CHO cells, served as positive controls for purificati on and detection procedures. For selective enrichment of IL-2R molecul es from supernatants and sera, affinity columns were prepared by coupl ing recombinant IL-2 or monoclonal antibodies against the alpha and th e beta chain of the IL-2R complex to cyanogen bromide-activated Sephar ose. Western blotting with affinity-purified fractions under reducing and nonreducing conditions revealed proteins that showed immunoreactiv ity for IL-2R alpha, beta, and gamma chain using several detection ant ibodies against these molecules. We conclude that the composition of s IL-2R in vivo is more complex than that of recombinant sIL-2R and can include all three IL-2R chains.