A special buffered ammonium sulfate fixative (Michel's fixative) designed for use as a liquid media capable of preserving in vivo tissue fixed immunoglobulins and complement was evaluated. The preservative ability of this fixative was studied by using skin biopsies from a confirmed case of spontaneously occurring equine pemphigus foliaceus. Once obtained, 16 skin biopsies were placed in Michel's fixative. Eight samples were stored at ambient temperature (21°C) and 8 samples were stored in a conventional refrigerator at 4°C. Over an 8 month time period, direct immunofluorescence was performed on these skin biopsies looking for the abnormal presence of IgG, IgM (when done) and C3 deposition within the intercellular spaces of the epidermis. The results of this study indicated that Michel's fixative was capable of preserving in vivo tissue fixed immunoglobulin and complement for 8 months. This was demonstrated by positive direct immunofluoresence spaces of the epidermis in all of the skin biopsies examined. In addition, it was shown that refrigerated and non-refrigerated skin biopsies in Michel's fixative both yielded a diagnostic quality of direct immunofluorescence. This will allow the mailing of skin biopsies without requiring refrigeration and specimens mailed in the winter should demonstrate reliable results on fluorescent antibody testing when performed.
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