Roscoe, Donna

Abstract Introduction The immune environment of the brain plays a major role in neurodegenerative conditions such as Alzheimer’s disease. The abnormally clean facilities in which laboratory mice are kept limit immune experience and cause major concerns regarding the translatability of research to humans. These facilities, although not germ-free, lack the normal exposures to diverse commensal and environmental microorganisms experienced by mice in the wild or diverse environments such as a pet store. By breeding inbred lab mice that have previously experienced exposure to the dirty bedding of pet store mice, we can generate “bred dirty” mice with immune systems that mirror those of adult humans more closely. It is unclear whether these immune changes extend to the brain and whether this plays a role in neurodegenerative disease. Methods We used the P301s transgenic mouse model of Alzheimer’s disease that accumulates age-dependent tau pathology. We exposed these mice to dirty bedding obtained from pet store mice, and bred them to establish a line of “bred dirty” tau-P301S mice and appropriate controls. At endpoint, we collected brain and spleen for flow cytometry, immunofluorescence, and bulk RNAseq. Results The proportions of CD3+ T cells, monocytes, and macrophages were significantly increased in the brains of the dirty tau-P301S mice compared to their clean tau-P301S counterparts. The brains of the dirty tau-P301S mice also showed an increase in the proportion of CD8+ T cells, specifically effector differentiated (CD62L-CD44+) CD8+ T cells. The proportion of activated (CD11c+) microglia was increased in tau-P301S mice but unaffected by dirty status. Conclusion Disease-associated infiltration of adaptive immune cells into the brain is amplified by dirty status without grossly affecting microglial activation. Given the increasingly recognized role of T cells in Alzheimer’s disease pathogenesis, our results suggest that more immune educated models might better represent the role of T cells in neurodegenerative disease. Funding Source Mayo Clinic and The Translational Genomics Research Institute Topic Categories Neuroimmunology (NEUR)

Abstract Description Rationale Mice are used for models of human diseases. The immune cell composition of specific-pathogen-free (SPF) mice closely resembles that of newborn humans. Adult humans have been exposed to a multitude of pathogens throughout their lives. In this project, we sought to create a mouse model resembling humans by co-housing SPF mice to pet store mice. Methods Male and Female SPF B6 mice were co-housed with pet store mice. Multiplexed PCR was used to assess pathogen transmission. After 2 months, lungs, small intestines, and colons were analyzed by high-dimensional mass cytometry and multiplexed cytokine assay. Results Co-housed male mice frequently succumbed to infection. After two months, co-housed males still exhibited signs of active infection across all organs examined including profound myeloid and T effector cell infiltration. In female mice, infection was less fatal and active sickness resolved by two months. Across tissues, T cells exhibited both memory and effector phenotypes. Increases in monocytes and granulocytes were observed in lungs and colons while CD8+ T cells increased in the small intestine. Importantly, innate lymphoid cells were not displaced but underwent phenotypic changes. Conclusion Asynchronous systemic exposure to multiple pathogens in mice results in dramatic alterations to the immune landscape in a sex- and tissue-dependent manner. When used in disease models, these mice may provide new insight beyond those obtained previously with SPF mice. Funding Sources •NIAID R37 AL71106 Topic Categories Mucosal and Regional Immunology (MUC)

Abstract Description Rationale Lab mice, although not germ-free, lack normal exposures to diverse commensal and environmental microorganisms. Dirty mice, as those found in the wild or in pet stores are referred to, have diverse microbiomes and history of infection with multiple pathogens; their immune systems mirror those of adult humans. It is possible to turn lab mice dirty by co-housing C57BL/6, or other genetically inbred mouse strains, with pet store mice or their dirty bedding. Due to concerns regarding aggression, dirty mouse studies typically only include female mice; if they do include male mice, they are co-housed with dirty bedding only. Methods We used divided rat cages to co-house C57BL/6J mice of both sexes for 8 weeks with either pet store mice or their dirty bedding before assessing pathogen transfer and immune profiles of brain and spleen. Results Live co-housing resulted in increased pathogen transfer and sex-dependent immune changes in brain and spleen compared to clean mice or dirty bedding alone. Co-housed males became ill later and more severely than females, showing active infection after 8 weeks while the illnesses of females had resolved. Conclusions These findings suggest that co-housing method is important in determining the changes that occur as lab mice get dirty. The sex-dependent nature of these changes suggests female-only dirty mouse studies are insufficient in representing the altered immunology of these immune-appropriate mouse models. Funding Sources Supported by Mayo Clinic Graduate School of Biomedical Sciences Topic Categories Mucosal and Regional Immunology (MUC)