Immunoglobulin A¡]IgA¡^, the principal antibody class in secretions that bathe mucosal surfaces, acts as an important first line of defense. However, some pathogenic bacteria such as Haemophilus influenzae can produce IgA1 proteases to impair IgA1, especially in human mucosal immune system. IgA1 proteases are characterized by a polypeptide precursor containing four domains, the signal peptide, protease, linking region and the £]-domain. The function of the protease and the £]-domain (£] core) had been studied extensively, but the linking region is less defined, let alone its function. To complete the project, the DNA fragment for linking region was amplified by PCR from iga gene (Gene Bank DQ683353) spanning from NT3130 to NT4686, and then transferred to pGEX-2T for expression. Recombinant linking region-protein was purified using glutathione-Sepharose column. The proliferation assay showed that purified recombinant protein did not enhance cell growth significantly at the concentration of 1 £gg/ml compared to either the negative control or GST control; but when the concentration of the recombinant protein was increased to 5 £gg/ml or 10 £gg/ml, the cell proliferation was significantly stimulated. These results suggest that recombinant linking region-protein contains special element that stimulates the jurkat cell.