Characterization of a murine lymphokine distinct from interleukin 2 and interleukin 3 (IL-3) possessing a T-cell growth factor activity and a mast-cell growth factor activity that synergizes with IL-3.

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Murine mast-cell and T-cell growth factor activities, distinct from interleukins 3 and 2 (IL-3 and IL-2), have been identified and partially purified from the supernatant of the activated helper T-cell line Cl.Ly1+2-/9. This mast-cell growth factor (MCGF) activity supports only low levels of proliferation of several IL-3-dependent mast-cell lines and synergistically enhances the growth of mast cells in the presence of IL-3. The T-cell growth factor (TCGF) stimulates the proliferation of several T-cell lines, but to a lesser extent than recombinant IL-2. The MCGF and TCGF activities were not separable despite multiple biochemical fractionations, suggesting that both activities reside in the same protein. The MCGF/TCGF was separated from endogenous IL-3 by cation-exchange chromatography at neutral pH and could be distinguished from IL-2 by unique elution conditions from reverse-phase columns. Two bands of MCGF/TCGF activity were eluted from gels after sodium dodecyl sulfate/PAGE; under nonreducing conditions, the activities corresponded to molecular masses of 20 and 15 kDa, while after reduction, the molecular masses were 21 and 16 kDa. Thus, both activities may correspond to single polypeptide chains. The majority of the MCGF/TCGF activity appears to reside in the 20-kDa species, which displays a pI of 6.2 on chromatofocusing.

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