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Objective-To evaluate the number of males per cage as a possible risk factor for murine ankylosing enthesopathy (Ammwr)-a spontaneous joint disease with parallels to human seronegative spondylarthropathies-since ANUr shows incomplete penetrance of genetic susceptibility factors among individuals living in a stable environment. Methods-Frequency of ANKENT was compared among males housed with females, with other males, or alone. Results-In three independent cohorts, a trend was observed that males housed with females rarely develop the disease, in contrast to males housed with other males (P < 0.25, P < 0.05, and P < 0.01). Furthermore, no males caged alone developed ANxENT, whereas disease did occur in males grouped together (P < 0.01). When healthy males (retired breeders) were recaged either alone or with other males, ANKENT developed among the grouped males only (P < 0.005). Conclusions-Caging males together is a relative risk factor for AKENT. Grouped caging may perturb the immune system through endocrine pathways or modify microbiological load through behaviour (for example, infection due to biting).

The role of MHC class I heterodimer expression in mouse ankylosing enthesopathy Weinreich, S.S.; Hoebe-Hewryk, B.; van der Horst, A.R.; Boog, C.J.P.; Ivanyi, P.

Murine ankylosing enthesopathy (ANKENT) is a spontaneous joint disease with numerous parallels to the human seronegative spondylarthropathies at the level of disease distribution, genetics and pathology. Although several genetic susceptibility factors have been identified previously, there is variation in disease susceptibility among genetically identical individuals, living in a stable environment. Preliminary observations indicate that males housed together with females rarely develop the disease, in contrast to males housed with other males (p < 0.25, p < 0.05, and p < 0.01). Furthermore, males caged under solitary conditions developed no ANKENT, whereas the disease did develop among individuals housed in groups of 4 (p < 0.01). The mechanism through which grouped caging induces a risk for ANKENT requires further study.

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