Modified aluminum (Al)-hematoxylin stain for detection of Al in sheep and cat tissues: an animal model for the study of Al-associated conditions.

Aluminum (Al) has been an effective adjuvant in vaccines for nearly a century in animals and humans. Al can induce persistent granulomatous inflammatory responses characterized by macrophages with large granular, blue-gray cytoplasm sometimes with intracytoplasmic structures known as crystalloid bodies. These granulomas have been linked to proliferative and neoplastic conditions at injection sites in animal and humans. The detection of Al in tissue is crucial but current methods are time-intensive and require specialized training. This study highlights the efficacy of the modified Al-hematoxylin (MAH) technique in animals. Tissues from Al-induced lesions in sheep and cats were examined, along with non-aluminum granulomas as controls and MAH results were confirmed with lumogallion staining. In sheep, MAH positively stained granuloma macrophages, crystalloid bodies, necrotic regions and nearby connective tissue macrophages, while lymphoid aggregates present in granulomas were consistently negative. Macrophages loaded with Al and crystalloid bodies in lymph nodes were also MAH-positive, as were macrophages in contaminated injection sites following application of commercial Al-based vaccines. In cats with Feline Injection Site Sarcoma (FISS), MAH detected macrophage clusters around the tumor periphery and within the sarcoma. This cost-effective, rapid, and specific technique provides valuable insights for diagnosing Al-related conditions and could serve as an animal model for other species, including humans.