CD21 Ligands Provide Better Antibody Specific Response Than The Polyclonal Stimulation in mBCs Activation

Objective: In this study, we evaluated if the CD21 activation through its free ligands can improve the in vitro assessment of antigen specific antibody response of mBCs. Methods: Amongst five healthy voluenteer, a volunteer with the highest level of anti-tetanus toxoid IgG (anti TT-IgG) antibody was detected by Enzyme-Linked Immunosorbent Assay (ELISA). The volunteer’s peripheral blood mononuclear cells (PBMNCs) obtained by ficoll method were treated following conditions in vitro; in the group 1) the polyclonal stimulation and CD21 soluble ligands were applied, in the group 2) antigen-specific stimulation by tetanus toxoid (TT) and CD21 soluble ligands were applied, in the group 3) the CD21 soluble ligands C3d, iC3b and IFNα in addition to the polyclonal stimulation and antigen-specific stimulation by TT were applied. Anti-TT-IgG and total IgG antibody quantities were determined in culture supernatants at the end of the day-12 by ELISA. Results: We found that total IgG antibody levels were higher in the 3th group where the soluble CD21 ligands added to the polyclonal stimulation and TT antigen. CD21 free ligand C3d was observed to increase specific antibody response together with TT antigen-specific stimulation. In addition, antigen-specific antibody responses were different depending on the CD21 free ligands. Conclusion: Antigen specific stimulation in combination with C3d provided stronger specific antibody responses than polyclonal stimulation. Our data indicate that CD21 free ligands may have a potential in determining specific antibody responses.