The following cytokines can be grouped into a single family on the basis of sequence similarities.

• Interleukin-6 (IL-6) [1] (also known as B-cell stimulatory factor 2 (BSF-2) or interferon β-2) is a cytokine that has a wide variety of biological functions. It plays an essential role in the final differentiation of B- cells into IG-secreting cells, as well as inducing myeloma/plasmacytoma growth, nerve cell differentiation and, in hepatocytes, acute phase reactants.
• Granulocyte colony-stimulating factor (G-CSF) [2] belongs to the cytokine family whose members regulate hematopoietic cell proliferation and differentiation. G-CSF exclusively stimulates the colony formation of granulocytes.
• Myelomonocytic growth factor (MGF) [3] is an avian hematopoeitic growth factor that stimulates the proliferation and colony formation of normal and transformed avian cells of the myeloid lineage.

These cytokines are glycoproteins of about 170 to 180 amino acid residues that contains four conserved cysteine residues involved in two disulfide bonds [4], as shown in the following schematic representation.

                       +--+     +---+
                       |  |     |   |
            xxxxxxxxxxxCxxCxxxxxCxxxCxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
                                **********

'C': conserved cysteine involved in a disulfide bond.
'*': position of the pattern.

The pattern developed for this family of proteins includes the last two cysteines as well as other conserved residues.