Evaluation of the antiviral, adjuvant and immunomodulatory effects of a [beta]-(1,4)-linked polymannose (Acemannan)

Abstract

This study examined the antiviral, adjuvant and immunomodulatory effects of acemannan (ACE-M), a long-chain polydispersed β-(1,4)-linked mannose polymer. Antiviral effects were determined in vitro. Newcastle disease virus (NDV) infected secondary chicken embryonic fibroblast (CEF) monolayers were cultured in the presence of ACE-M and molecular and biological procedures were used to evaluate effects. Adjuvant and immunomodulatory effects of in vivo administration of ACE-M were evaluated using enzyme-linked immunosorbent assay (ELISA) procedures. The same procedures were used to evaluate the effects of in ovo presentation of ACE-M. An ACE-M concentration of 50 μg ml⁻¹ completely inhibited virus replication and following further evaluation using slide hemagglutination and hemadsorption tests, it was postulated that ACE-M alters the functional properties of the NDV glycoproteins, HN and F. To assess ACE-M's effects on viral glycoproteins, NDV-infected CEFs were treated with either 50 or 100 μg ml⁻¹ ACE-M and labeled with (³⁵S) -methionine or (³H) -glucosamine at selected intervals. Both HN and F glycoproteins were then radioimmunoprecipitated and analyzed by electrophoresis on a sodium dodecyl sulfate polyacrylamide gel (SDS-PAGE). Reduction in electrophoretic mobility of both HN and F was observed. Changes were dependent on time of treatment and concentration. It was hypothesized that changes in electrophoretic mobility were due to inhibition of the processing of HN and F glycoprotein oligosaccharides. To test this hypothesis, viral glycoproteins from NDV-infected cultures treated with ACE-M, deoxynojirimycin and deoxymannojirimycin and labeled with (³⁵S) -methionine were immunoprecipitated and analyzed by SDS-PAGE. HN and F glycoproteins immunoprecipitated from ACE-M- and deoxynojirimycin-treated cultures exhibited similar electrophoretic mobilities suggesting ACE-M or a metabolite thereof may block glucosidase I and thereby inhibit the processing of oligosaccharides and the post-translational processing of the glycoproteins, resulting in the production of non- or partially-functional glycoproteins. With respect to the adjuvant and immunomodulatory effects, ACE-M was shown to function primarily as an adjuvant. ACE-M added to either a monovalent or trivalent vaccine and presented in vivo significantly enhanced the immune response to both glycosylated and non-glycosylated antigens. Immunomodulatory effects of ACE-M were most pronounced when ACE-M was inoculated in ovo and antigen was presented on day one of hatch. This method caused a significant increase in antibody titers compared to other methods and may be expected to alter vaccination technology.