GROUPED CAGING PREDISPOSES MALE-MICE TO ANKYLOSING ENTHESOPATHY

Objective-To evaluate the number of males per cage as a possible risk factor for murine ankylosing enthesopathy (ANKENT)-a spontaneous joint disease with parallels to human seronegative spondylarthropathies-sin ce ANKENT shows incomplete penetrance of genetic susceptibility factor s among individuals living in a stable environment. Methods-Frequency of ANKENT compared among males housed females, with other males, or al one. Results-in three independent cohorts, a trend was observed that m ales housed with females rarely develop the disease, in contrast to ma les housed with other males (P < 0.25, P < 0.05, and P < 0.01). Furthe rmore, no males caged alone developed ANKENT, whereas disease did occu r in males grouped together (P < 0.01). When healthy males (retired br eeders) were recaged either alone or with other males, ANKENT develope d among the grouped males only (P < 0.005). Conclusions-Caging males t ogether is a relative risk factor for ANKENT. Grouped caging may pertu rb the immune system through endocrine pathways or modify microbiologi cal load through behaviour (for example, infection due to biting).