Circulating Foamy Macrophages and other features of Bacillus Calmette-Guérin challenge in Golden Syrian Hamsters

Authors: Putz, Ellie; ANDREASEN, CLAIRE - Iowa State University; Stasko, Judith; HAMOND, CAMILLA - Animal And Plant Health Inspection Service (APHIS); Olsen, Steven; Nally, Jarlath; Palmer, Mitchell

Submitted to: Vaccine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: While laboratory mice and rats are heavily utilized for clinical and veterinary animal models, they are not appropriate for the study of some diseases such as leptospirosis as they do not present with acute symptoms. The Golden Syrian hamster however, develops severe clinical signs in response to leptospirosis infection. Previously while characterizing the immune response to Leptospira challenge, our group determined that hamsters develop circulating foamy macrophages. These rare cells are most famously associated with tuberculosis granulomas, and not typically found in blood. This study addresses if hamsters will produce foamy macrophages in response to other bacteria besides Leptospira. Since foamy macrophages are already associated with Mycobacterium, hamsters were challenged with Bacille Calmette–Guérin (BCG), an attenuated human tuberculosis vaccine. Hamsters formed granulomas and generated foamy macrophages in response to vaccination. Further characterization of the role of these cells in hamster disease pathogenesis is of interest. Collectively, this supports that the formation of foamy macrophages is a hamster specific response to numerous bacteria and suggests hamsters may be a unique model for these cell types in the context of tuberculosis.

Technical Abstract: Golden Syrian Hamsters are utilized as rodent research models for various bacterial diseases. They are highly susceptible to Leptospirosis, making hamsters the most common model for testing and maintaining virulence of laboratory Leptospira strains as well as for bacterin vaccine efficiency testing. Hamsters are also used for modeling features of Bacillus Calmette–Guérin (BCG) and tuberculosis, as they consistently develop granulomas, differing from other BCG animal models. Circulating foamy macrophages have recently been identified in the blood of the hamsters following Leptospira challenge but not in controls. It has been unknown whether this phenomenon is specific to Leptospira/hamster interactions, or whether hamsters will produce circulating foamy macrophages in response to other bacterial infections. In this study, we established that hamsters develop circulating foamy macrophages when challenged intraperitoneally with BCG or Leptospira. In addition to circulating foamy macrophages, hamsters infected with BCG had widespread granuloma formation in major organs and injection sites also contained resident foamy macrophages, as well as mineralized bodies, sometimes containing acid fast bacteria.