Cloning and Expression of a Gamma-interferon-inducible Gene in Monocytes: a New Member of a Cytokine Gene Family

To define activation-specific sequences in human peripheral blood lymphocytes (PBL), a cDNA library was constructed by subtractive hybridization using resting and stimulated PBL pairs. Stimulation of PBL was achieved by triggering with mitogenic anti-CD2 (T11) monoclonal antibodies. Differential library screening with cDNA probes derived from stimulated versus resting PBL led to identification of two novel sequences, termed HC11 and HC14. The predicted primary and secondary structure of HC11 deduced from the translated nucleotide sequence suggests that the gene encodes a secreted protein of 99 amino acids (aa), including a 23 aa residue leader sequence. Surprisingly, Northern blot analysis demonstrated that HC11 mRNA is induced predominantly in peripheral blood non-T cells. Subsequently, we observed that the HC11 mRNA is induced in macrophages and the monocytic line U-937 by gamma-IFN, raising the possibility that T cell-derived gamma-IFN induced upon anti-CD2 stimulation activated monocytes to express HC11 RNA. In support of this notion, neutralizing anti-gamma-IFN monoclonal antibody inhibits the induction of HC11 mRNA in PBL activated through anti-CD2 antibodies. These findings suggest that there is a molecular cascade involving T cell-produced lymphokines and monokines which serve as a means for intercellular communication. Transient expression of HC11 cDNA results in a readily detectable specific set of protein bands in SDS-PAGE analysis of supernatants from radio-labeled COS cells, consistent with HC11 encoding a secreted product(s). Protein sequence comparison reveals homology with other members of a recently described inducible cytokine family whose functions are yet to be defined.