Conjugation of protein antigen to microparticulate β-glucan from Saccharomyces cerevisiae: A new adjuvant for intradermal and oral immunizations

Department of Microbiology and Immunology, University of Nevada School of Medicine, Reno, NV 89557, USA.
Applied Microbiology and Biotechnology (Impact Factor: 3.34). 09/2008; 80(6):1053-61. DOI: 10.1007/s00253-008-1618-8
Source: PubMed


Immunostimulatory glucose polymers known as beta-glucans have been studied for many years. Our laboratory has prepared and characterized a novel microparticulate beta-glucan (MG) from the budding yeast Saccharomyces cerevisiae. Because MG particles are rapidly phagocytized by murine peritoneal macrophages and induce the expression of B7 costimulatory molecules, we hypothesized that MG could serve as a vaccine adjuvant to enhance specific immune responses. Here, we describe a procedure for conjugating the test vaccine antigen bovine serum albumin (BSA) to MG via water-soluble carbodiimide linkage. Conjugates with up to 0.4 mg of BSA/mg MG were prepared. MG/BSA conjugates were still actively phagocytized by mouse peritoneal macrophages. When used to immunize mice by the intradermal route, these conjugates enhanced the primary IgG antibody response to BSA in a manner comparable to the prototypic complete Freund's adjuvant. Although primary oral immunization with MG/BSA caused no increase in serum anti-BSA antibody titers, booster immunization elicited a significant anti-BSA antibody response. These results suggest that protein antigens can be conjugated to MG via a carbodiimide linkage and that these conjugates provide an adjuvant effect for stimulating the antibody response to the protein antigens.

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    • "An overview of all required steps to synthesize these antibody functionalized GPs is given in Figure 1. First, protein G was conjugated to the particles via carbodiimide crosslinker chemistry [18] [32] [33]. Briefly, BSA-FITC GPs (500 µg/ml) were centrifuged (500 g, 5 min) and resuspended in 1 ml 2-(N-morpholino)ethanesulfonic acid (MES) buffer (0.1 M MES; pH 6.0). "
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    • "This was surprising because a number of studies have used β-glucan supplementation as a method of improving immune responses. Many studies demonstrating positive effects of β-glucans on immunity have used Balb/c mice (Berner et al., 2008; Harnack et al., 2009; Torello et al., 2010; Zhou et al., 2009), thus we are confident that this mouse model is appropriate for studies such as the one described here. "
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