Members of the interleukin-17 cytokine family are present in a variety of tissues (1-3), although the founding member, interleukin-17, is expressed exclusively in T cells and B cells (4-8). The cloning and characterization of a novel single-pass transmembrane protein with limited homology to the interleukin-17 receptor is reported. High mRNA levels were detected in prostate, cartilage, kidney, liver, heart, and muscle, whereas transcripts were barely detected in thymus and leukocytes. At least 11 RNA splice variants were found, transcribed from 19 exons on human chromosome 3p25.3-3p24.1. Differential exon usage was found in different tissues by quantitative reverse transcriptase-PCR. Predicted proteins range from 186 to 720 amino acids. Soluble secreted proteins lacking transmembrane and intracellular domains are predicted from several splice isoforms and may function as extracellular antagonists to cytokine signaling by functioning as soluble decoy receptors. Using antibodies directed at the cytoplasmic and extracellular domains of this protein, we investigated its localization and found that it was expressed in a variety of normal human tissues including prostate and in prostate cancer.