Expression of biologically active monomeric form of human M-CSF in baculovirus infected silkworm, Bombyx mori

The human macrophage colony stimulating factor (hM-CSF) in its monomeric form has been over-produced in BmN cells and in silkworm larvae infected with the recombinant baculovirus Bm284M-CSF. The recombinant monomeric M-CSF (rhM-CSF) exhibited the activity of 8-14 x 10(4) units/ml of cell culture medium. When the insect larvae were infected with the recombinant virus, the maximum rhM-CSF was expressed 4-5 days post infection with an activity of 3 x 10(6) units/ml hemolymph. The monomeric rhM-CSF was purified to homogeneity through three steps of purification. A pilot purification yielded 1 mg of homogeneous monomeric rhM-CSF from 10 larvae. The purified rhM-CSF monomers gradually dimerized in vitro. In contrast, the crude or the semi-purified monomers did not dimerize in vitro, indicating that the presence of an unknown moiety in the rhM-CSF preparations obtained from hemolymph interfered with dimerization.