A cytologic spin on vax adjuvant
Adjuvant often appears like this globby magenta material on cytology, but interestingly, sometimes vaccine adjuvant can be blue!
There was a study in Vet Clin Path that looked at this and found that Imrab 3 (rabies vax) adjuvant will stain this way with routine staining (link to that study here).
Here is a case I had of a vaccine hypersensitivity reaction to a rabies vaccine, and you can see the macrophages contain a bunch of blue material, consistent with adjuvant. Heads up though, other material can look like this (e.g. phagocytized cystic material, for example), so history needs to fit.