Interleukin-4/interleukin-13 Interleukin-4 (IL-4) is a cytokine that plays a central role in the control and regulation of the immune and inflammatory system [<cite idref="PUB00002013"/>, <cite idref="PUB00000107"/>]. IL-4 is a participant in several B-cell activation processes. It also stimulates othercell types such as T cells or mast cells. IL-4 is a glycoprotein that contains three disulphide bonds [<cite idref="PUB00000339"/>].<p>Interleukin-13 (IL-13) is a pleiotropic cytokine which may be important in the regulation of the inflammatory and immune responses [<cite idref="PUB00004143"/>].</p><p>The sequences of IL-4 and IL-13 are distantly related.</p>