Dengue virus-induced helper cytokine has two polypeptide chains which bear different determinants.

Dengue type 2 virus (DV) induces generation of a T cell helper cytokine (HF) in mouse spleen which enhances the antigen-specific antibody plaque forming cell count in syngeneic mice. The present study was undertaken to investigate the molecular structure of HF. It was observed that the activity of HF was abrogated by treatment with reducing agents such as glutathione, ouabain or dithiothreitol (DTT) which cleave disulphide bonds, separating the polypeptide chains. The two polypeptide chains could be purified by high performance liquid chromatography of DTT treated HF. The individual chains had no helper activity, but it could be restored by mixing the two. One chain of the HF bonded to the DV-antigen coupled immunosorbent column and the other to the anti-I-Ak antibody coupled column. Thus, DV-induced HF is a disulphide bonded double chain structure, one chain having antigen and the other having I-A determinants; the presence of both chains is essential for helper activity.