Local Skin Response due to Subcutaneous Injection of Monosodium Urate (MSU) Crystals in Mice

Abstract

We have reported that monosodium urate (MSU) crystals show the distinct advantages of a protein carrier binding with positively charged proteins and delivering antigenic protein into dendritic cells (DC), as well as an adjuvant promoting DC maturation and inducing cytotoxic T lymphocytes in vitro. However, the biological reaction due to subcutaneous injection of the MSU crystals remains unclear.
Therefore, here, we investigated the morphological changes after the administration of MSU crystals or uric acid powders in mice. In addition, the skin reaction at the injection site was observed. The slide sections indicated that treatment with the MSU crystals caused acute inflammatory responses with the migration of activated monocytes which engulfed the fragmentary MSU crystals. On the other hand, the implantation of uric acid powders barely induced any inflammatory cells except for small number of mononuclear cells. In comparison with the morphological differences, neither MSU crystals nor uric acid powders resulted in local skin abnormalities, including rash, swelling, and fever.
These findings suggest that the subcutaneous injection of MSU crystals was relatively safe, and that the crystals are available as a promising protein carrier of cancer vaccine peptides in vivo.