Tannic Acid, as a Structural Moiety Coupled to a Protein Antigen, Exhibiting a Molecular-structure Adjuvant Activity for Antibody Specificity Enhancement

Abstract

Background: An antigen is a small foreign substance, such a microorganism structural-protein, that may trigger an immune response once inside the body. Antigens are preferentially used rather than a complete attenuated microorganism to develop safe vaccines. Unfortunately, not all antigens are able of inducing an immune response. Thus, new adjuvants seeking to enhance the antigen’s ability to stimulate immunity must be developed. Therefore,the objective of this work was to evaluate the molecular-structure adjuvant activity of tannic acid (TA) coupled to a protein antigen in Balb/c mice. Method: Bovine serum albumin (BSA) was used as an antigen. The coupling of BSA and TA was mediated by carbodiimide crosslinking, and verified by SDS-PAGE. Forty-two Balb/c mice were divided into seven groups including two controls without antigen, an antigen control, an adjuvant control, and two treatment groups. An additional group was used for macrophages isolation. A 30-day scheme was used to immunize the mice. The analysis of humoral immunity included immunoglobulin quantification, isotyping and antigen-antibody precipitation. The analysis of cell-mediated immunity included the quantification of nitric oxide from peritoneal macrophages and splenocytes’ proliferation assay, after treatment stimulation. Results: No differences were found in the antibodies’ concentration or isotypes induced with the conjugate or the pure BSA. However, an immunogenicity improvement (p<0.05) was observed through the specific anti-BSA antibody titles in mice immunized with the conjugate. Besides, macrophage activation (p<0.05) was detected when stimulated with the treatments containing TA. Conclusion: Tannic acid exhibited macrophages’ activation properties. Moreover, when TA is incorporated into the structure of a protein antigen such as BSA, an antibody specificity enhancement is observed. This as a consequence of antigen processing by activated antigen-presenting cells. These results showed the use of tannic acid as a novel candidate for vaccine molecular-structure adjuvant.