Influence of Surface Charge of PLGA Particles of Recombinant Hepatitis B Surface Antigen in Enhancing Systemic and Mucosal Immune Responses

This study investigates the efficacy of surface-modified microspheres of hepatitis B surface antigen (HBsAg) in eliciting systemic and mucosal immune responses. Positively charged poly(D,L-lactic-co-glycolic acid) microspheres were prepared by a double-emulsion solvent-evaporation method with cationic agents--stearylamine and polyethylenimine--in the external aqueous phase. Formulations were characterized for morphology, size, density, aerodynamic diameter, entrapment efficiency and in vitro drug-release profile. Immunization was performed after pulmonary administration of the formulations to female Sprague-Dawley rats and the immune response was monitored by measuring IgG levels in serum and secretory (sIgA) levels in salivary, vaginal and bronchoalveolar lavage fluids. The cell-mediated immune response was studied by measuring cytokine levels in spleen homogenates, and a cytotoxicity study was performed with Calu-3 cell line. The aerodynamic diameter of the particles was within the respirable range, with the exception of stearylamine-modified particles. Zeta potential values moved from negative (-6.76 mV) for unmodified formulations to positive (+0.515 mV) for polyethylenimine-modified particles. Compared to unmodified formulations, polyethylenimine-based formulations showed continuous release of antigen over a period of 28-42 days and increased levels of IgG in serum and sIgA in salivary, vaginal and bronchoalveolar lavage. Further, cytokine levels-interferon gamma and interleukin-2-were increased in spleen homogenates. The viability of Calu-3 cells was not adversely affected by the microparticles. In summation, this study establishes that positive surface charges on poly(D,L-lactic-co-glycolic acid) particles containing HBsAg enhances both the systemic and mucosal immune response upon immunization via the respiratory route.