The Effect of Delivery Systems on the Induction of T Helper 1 Cell Response to an ESAT6-Like Protein Rv3619c and Identification of Its Immunodominant Peptides

Abstract

<b><i>Objective:</i></b> This study determined the effects of chemical adjuvants, incomplete Freund’s adjuvant (IFA) and aluminum hydroxide (Alum), mycobacteria, and a DNA plasmid as delivery systems on the induction of protective Th1 (interferon-gamma (IFN-γ)) and nonprotective Th2 (IL-5) and Treg (IL-10) cytokine responses to Rv3619c and its peptides. Rv3619c is an immunodominant <i>Mycobacterium tuberculosis</i>-specific antigen and belongs to the early-secreted antigenic target of 6 kDa-family of proteins. Delivery systems are needed to deliver such antigens in animal models and induce protective immune responses. <b><i>Methods:</i></b> The <i>rv3619c</i> gene was amplified from the genomic DNA of <i>M. tuberculosis</i> and cloned into appropriate vectors for expression in <i>Escherichia coli</i>, <i>Mycobacterium smegmatis</i>, and eukaryotic cells. Spleen cells from mice immunized with <i>rv3619c</i> using different delivery systems were stimulated in vitro with synthetic peptides (P1 to P6) of Rv3619c, and secreted cytokines were estimated by ELISA. <b><i>Results:</i></b> The recombinant <i>M. smegmatis</i> and DNA plasmid induced the secretion of the protective cytokine IFN-γ in response to peptide-pool of Rv3619c and all the individual peptides, whereas rv3619c/IFA induced the secretion of IFN-γ in response to the peptide pool, and the peptides P5 and P6. However, the secretions of the nonprotective cytokines IL-5 and IL-10 were induced to none of the peptides with the delivery systems used. <b><i>Conclusion:</i></b> Rv3619c is a major antigen of <i>M. tuberculosis</i> with multiple immunogenic epitopes; however, immune responses to individual epitopes can vary based on delivery systems used.