Murine hybridoma/plasmacytoma growth factor: Complete amino‐acidsequence and relation to human interleukin‐6

Murine interleukin‐HP1 (HP1) was originally identified as a T‐cell derived lymphokine with growth factor activity for B‐cell hybridomas and plasmacytomas. This growth factor was recently shown to stimulate both normal B‐cell differentiation and T‐cell growth factor activity. We have determined the complete amino acid sequence of HP1 on 40 μg (approximately 2 nmol) protein using a combination of sensitive microbore column (1.0 and 2.1 mm internaldiameter) HPLC, peptide mapping and automated amino acid microsequence analysis. Ion‐pairing chromatography was employed to isolate hydrophilic peptides which were not retained on conventional reversed‐phase HPLC systems. The molecule consists of 187 amino acid residues with a calculated molecular mass of 21710 Da. Although there is virtually no similarity between the NH₂‐terminal region of HP1 and its human biological counterpart (26‐kDa protein/interferon‐β₂= B‐cell stimulatory factor‐2/interleukin‐6), these studies demonstrate extensive amino acid similarity inthe middle and COOH‐teminal regions of these molecules suggesting that HP1 is the murine homologue of human interleukin‐6.