Identification of blue staining vaccine-derived material in inflammatory lesions using cultured canine macrophages

Vaccine reactions are described in cytology textbooks as having eosinophilic to magenta colored globules within and admixed with inflammatory cells. Recently, we have seen increased numbers of inflammatory lesions containing blue to blue-gray globular material, with historical information suggesting an association with rabies vaccination.

The purpose of the study was to confirm the blue-gray and the eosinophilic material observed microscopically in some inflammatory lesions as being vaccine-derived.

Three different vaccines were cytocentrifuged and Wright stained. Vaccine aliquots were also added to the culture media of canine-derived macrophages for 24 hours and the cells subsequently harvested, cytocentrifuged, and Wright stained. The globular material present in both preparations was compared to that observed in vaccine-induced inflammatory lesions. Morin staining was used to identify metal within vaccine material in both in vitro- and in vivo-derived cytology samples.

Vaccine-derived material has a characteristic color and appearance. Appearance of the material was consistent in cytologic samples, in cells incubated with the vaccine, and in cytocentrifuged preparations of the vaccine vial contents. The blue-gray globules stained positively for Morin stain, while the eosinophilic material did not stain.

Vaccine-induced inflammatory lesions may contain blue to blue-gray or magenta stained globular material. Blue-gray material was associated with administration of rabies vaccine Imrab 3 TF and the observed material may be metal-containing adjuvant. Magenta material was associated with other vaccines and negative for Morin stain, suggesting a metal-free adjuvant.