The myeloid blood cell differentiation-inducing protein MGI-2A is interleukin-6.

The mouse myeloid blood cell differentiation-inducing protein, macrophage and granulocyte inducer, type 2A (MGI-2A), was purified, and the amino acid sequence of a CNBr cleavage peptide (22 residues) was determined. This amino acid sequence is identical to the sequence found in positions 73 to 94 of mouse interleukin-6 (IL-6). Recombinant mouse IL-6 protein induces differentiation of mouse myeloid leukemic cells that are induced to differentiation by MGI-2, and monoclonal antimouse-MGI-2 antibody, which neutralizes MGI-2, also completely neutralizes this IL-6-induced differentiation. These results show that the major type of mouse myeloid differentiation-inducing protein (MGI-2A) and IL-6 are very similar and most likely identical proteins. Recombinant human IL-6 (also called interferon-beta 2 or B-cell differentiation factor), which shows only a 41% similarity to mouse IL-6, has 11 identical amino acid residues out of the 22 in the mouse MGI-2A peptide and also induces differentiation of the same myeloid leukemic cells.