Expression of fusion protein pIL6-IL2 in E. coli and bio-activity assay

Interleukin-2 and Interleukin-6 can stimulate T-lymphocytes proliferation and B-lymphocytes secreting immunoglobulins respectively, further enhance animal's cellular and humoral immune responses. Moreover, IL2 and IL6 can co-adjust biological activities between them. Hence, two cDNAs of the mature porcine IL6 (pIL6) and that of pIL2 were linked by a sequence with translating GGGGSEFGSGG and cloned into E.coli expression plasmid pET-28a. The fusion protein pIL6-IL2 was expressed in BL21 (DE3) with 40kDa of molecular weight by SDS-PAGE. The expression level reached to 66.26% and enhanced to 85.66% by purification. Analysis by cell proliferations of IL6-dependent cell B9 and IL2-dependent cell CTLL, the bio-activity units of the fusion protein IL6-IL2 can reach 0.8×10~(3)U/mg and 6.4×10~(3) U/mg respectively.