Soluble antigens from the neurotropic pathogen Angiostrongylus cantonensis directly induce thymus atrophy in a mouse model

Thymic atrophy induced by Plasmodium berghei ANKA and Plasmodium yoelii 17XL infection

The thymus is the anatomical site where T cells undergo a complex process of differentiation, proliferation, selection, and elimination of autorreactive cells which involves molecular signals in different intrathymic environment. However, the immunological functions of the thymus can be compromised upon exposure to different infections, affecting thymocyte populations. In this work, we investigated the impact of malaria parasites on the thymus by using C57BL/6 mice infected with Plasmodium berghei ANKA and Plasmodium yoelii 17XL; these lethal infection models represent the most severe complications, cerebral malaria, and anemia respectively. Data showed a reduction in the thymic weight and cellularity involving different T cell maturation stages, mainly CD4-CD8- and CD4+CD8+ thymocytes, as well as an increased presence of apoptotic cells, leading to significant thymic cortex reduction. Thymus atrophy showed no association with elevated serum cytokines levels, although increased glucocorticoid levels did. The severity of thymic damage in both models reached the same extend although it occurs at different stages of infection, showing that thymic atrophy does not depend on parasitemia level but on the specific host-parasite interaction.

A restored humoral environment ameliorates acute brain injury after Angiostrongylus cantonensis infection

Circulating factors in the circulatory system support important functions of living tissues and the body. Parabiosis is a condition in which two living animals are connected using surgical methods and share a single circulatory system. Angiostrongylus cantonensis is the major cause of infectious eosinophilic meningitis, which causes severe damage to the central nervous system (CNS) and immune system. However, the mechanism of immunopathology remains largely unknown. We hypothesize that a restored humoral environment can help relieve damage to the CNS and immune system. In the present study, we found that administration of normal serum significantly reduced mortality, alleviated thymic atrophy and reduced inflammation in the brains of mice infected with A. cantonensis. We further generated parabiotic pairs between two healthy mice, one of which was then orally infected with A. cantonensis. The results showed that compared with singleton mice, mice connected with a healthy parabiotic partner were protected against CNS and immune system damage, as revealed by significantly reduced inflammation in the brain, alleviated thymic atrophy, and decreased expression of proinflammatory cytokines. These findings revealed that a healthy systemic environment can relieve damage to the CNS and immune system in infected mice, suggesting novel therapeutic approaches for diseases involving severe brain and immune system damage.

Infection-Associated Thymic Atrophy

The thymus is a vital organ of the immune system that plays an essential role in thymocyte development and maturation. Thymic atrophy occurs with age (physiological thymic atrophy) or as a result of viral, bacterial, parasitic or fungal infection (pathological thymic atrophy). Thymic atrophy directly results in loss of thymocytes and/or destruction of the thymic architecture, and indirectly leads to a decrease in naïve T cells and limited T cell receptor diversity. Thus, it is important to recognize the causes and mechanisms that induce thymic atrophy. In this review, we highlight current progress in infection-associated pathogenic thymic atrophy and discuss its possible mechanisms. In addition, we discuss whether extracellular vesicles/exosomes could be potential carriers of pathogenic substances to the thymus, and potential drugs for the treatment of thymic atrophy. Having acknowledged that most current research is limited to serological aspects, we look forward to the possibility of extending future work regarding the impact of neural modulation on thymic atrophy.