Hyaluronan is an anionic polysaccharide and a major component of extracellular matrices. The major physiological roll of hyaluronan (hyaluronic acid, HA) is thought to be a space filling material and HA is an attractive biomaterial due to its biocompatibility and biodegradability. We chemically modified ovalbumin (OVA), a well defined protein antigen, with HA to reduce its immunogenicity. HA was enzymatically fragmented by a hyaluronidase and different sizes of fragments (Mn=3000 and 9000) were obtained. The enzyme-digested HA fragments have a reducing end, which was used for coupling with OVA through reductive amination reaction. Colorimetric assay for free amino groups in OVA indicated that the conjugated number of HA fragments was maximally 10 and 6 per OVA, for the smaller (Mn=3000) and larger (Mn=9000) HA fragments, respectively. The HA contents of the conjugates were calculated as 40 and 55 wt%, respectively. We also obtained HA conjugates that have different length but almost the same number of HA fragments on OVA. The mice injected with the HA-conjugated OVA showed considerably lower OVA-specific IgE production than those with native OVA, implying reduced immunogenicity of OVA by the HA-modification. The data suggest that HA is a useful biomaterial for modification of immunological information in antigenic proteins.
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