Stressors increase leptin receptor-expressing thymic epithelial cells in the infant/child thymus.

The thymus, the organ that is the most sensitive to stress, presents acute involution as a result of exposure to strong stress in childhood. Thymic involution is thus often considered evidence of child abuse/neglect in forensic autopsies. A portion of the thymic epithelial cells express leptin receptor, and leptin showed a thymo-protective function against stress-induced thymic involution in an animal model. Leptin receptor-expressing thymic epithelial cells (LR-TECs) may play a key role in the thymic remodeling provoked by a stressful environment. Here, we sought to clarify the changes of histopathological findings and human LR-TECs in stressful environment. We examined human thymus specimens obtained from 40 forensic autopsy cases (26 male, 14 female; age 21 to 3221 days). We divided the cases into stressor-positive (SP, n = 29) and stressor-negative (SN, n = 11) groups. Cases were classified according to the histological classification of thymic involution and investigated by leptin receptor immunostaining. The results revealed that (1) the SP group showed obvious histological thymic involution (p < 0.01) and (2) the LR-TECs/TECs ratio in the cortex was markedly and significantly increased in the SP group compared to the SN group (p < 0.01). The increase in the cortical LR-TECs/TECs ratio in the SP group may be part of the stress response mechanism in the human thymus. We thus speculate that the quantification of LR-TECs in the thymic cortex is a valuable stress marker for forensic autopsy cases.