Interleukin-4/interleukin-13, conserved site <p>Interleukin-4 (IL-4) [<cite idref="PUB00000107"/>] is a cytokine that plays a central role in the control and regulation of the immune and inflammatory system. IL-4 is a participant in several B-cell activation processes. It also stimulates other cell types such as T cells or mast cells. IL-4 is a glycoprotein of 110 to 131 residues. It contains three disulphide bonds. The position of these disulphide bonds is not highly conserved since the topology of two of them differs in Human and mouse IL-4 [<cite idref="PUB00000339"/>]. </p><p>Interleukin-13 [<cite idref="PUB00004143"/>] (IL-13) is a recently discovered pleiotropic cytokine, which may be important in the regulation of the inflammatory and immune responses. IL-13 is a glycoprotein of 110 residues. </p><p>The sequence of IL-4 and IL-13 are distantly related. The N-terminal part of these proteins contains a cysteine, which in IL-4, is involved in the sole disulphide bond conserved between human and mouse IL-4. </p>