Primary immune effects of eukaryotic expression plasmids encoding two hyperactive mutants of human soluble B lymphocyte stimulator.

B lymphocyte stimulator (BLyS), a ligand belonging to the tumor necrosis factor (TNF) family, plays a critical role in regulating survival and activation of peripheral B cell populations during humeral immune responses. Among the TNF family members, BLyS is unique in that it contains an unpaired Cys residue (Cys146) at the corresponding position where some other members have about 37.5% (6/16) Ala or 37.5% (6/16) Val. Here, with eukaryotic expression vector pcDNA3.1(-), we mutated Cys146 to Ala or Val and constructed two mutant eukaryotic expression plasmids of the human soluble BLyS, pcDNA3.1BY-A and pcDNA3.1BY-V. Following repetitive subcutaneous injection of these expression plasmids in BALb/C mice, the wild-type and mutant BLyS proteins were detectable in the blood of treated animals over several weeks. In addition, the expression of these proteins induced specific IgG but not IgM responses. The implications of the results are discussed.