The 2022 mpox virus outbreak was sustained by efficient human-to-human transmission and spread predominantly through sexual networks of men who have sex with men (MSM). It is currently unclear what combination of factors resulted in the enhanced transmission. To investigate this, we established the peridomestic African rodent Mastomys natalensis as a new rodent model susceptible to infection after intraperitoneal, rectal, vaginal, and transdermal inoculation with an early 2022 human outbreak isolate (Clade IIb). Route-dependent shedding and tissue replication occurred in the presence of self-resolving localized skin, reproductive tract, or rectal lesions. Mucosal inoculation via both the rectal and vaginal route led to increased shedding compared to skin inoculation, and increased replication and a proinflammatory T-cell profile. Contact transmission was higher in rectally inoculated animals. This suggests that the spread in MSM communities may have been enhanced by increased susceptibility of the anal and genital mucosae for infection and subsequent virus release.

Stem cell engraftment is currently a promising approach for type 1 diabetes mellitus (T1DM) treatment. In our previous study, engraftment of a combination of human amniotic epithelial cells (hAECs) and hyaluronic acid (HA) showed potent anti-diabetic effect in streptozotocin (STZ)-induced T1DM mice via tail vein injection. Here, we adopted a different route of stem cell delivery, that is via pancreatic subcapsular transplantation. This combined local engraftment of hAECs and HA in STZ-induced T1DM rats showed potent anti-diabetic activity, leading to stronger hypoglycaemia, more intact islet structure and increased number of insulin-positive cells compared with those with hAECs or insulin treatments. Engraftment of hAECs alone increased the proportion of Th1 and T-reg cells and decreased the proportion of Th2 and Th17 cells to protect islet β cells in STZ-induced T1DM rats, whereas the combined engraftment of hAECs and HA showed more potent regulatory capacity, considerably decreased the level of TNF-α and IL-17 and increased the level of TGF-β1 compared with those by other treatments. The potent synergistic effect of HA contributed to the recovery of immune balance in the diabetic rat model, thereby suggesting a new strategy for effective treatment of T1DM.
© 2023 The Scandinavian Foundation for Immunology.

The multimammate mouse (Mastomys natalensis; M. natalensis) has been identified as a major reservoir for multiple human pathogens including Lassa virus (LASV), Leishmania spp., Yersinia spp., and Borrelia spp. Although M. natalensis are related to well-characterized mouse and rat species commonly used in laboratory models, there is an absence of established assays and reagents to study the host immune responses of M. natalensis. As a result, there are major limitations to our understanding of immunopathology and mechanisms of immunological pathogen control in this increasingly important rodent species. In the current study, a large panel of commercially available rodent reagents were screened to identify their cross-reactivity with M. natalensis. Using these reagents, ex vivo assays were established and optimized to evaluate lymphocyte proliferation and cytokine production by M. natalensis lymphocytes. In contrast to C57BL/6J mice, lymphocytes from M. natalensis were relatively non-responsive to common stimuli such as phytohaemagglutinin P and lipopolysaccharide. However, they readily responded to concanavalin A stimulation as indicated by proliferation and cytokine production. In summary, we describe lymphoproliferative and cytokine assays demonstrating that the cellular immune responses in M. natalensis to commonly used mitogens differ from a laboratory-bred mouse strain.

Bacterial translocation (BT) is thought to play an important role in the development of liver cirrhosis, but the mechanisms have not been fully explored. This study aims to investigate the distribution of Treg (CD3+CD4+CD25+Foxp3+), Th17 (CD3+CD4+IL-17+), and Th1 (CD3+CD4+IFN-γ+) cells in the intestinal lamina propria, liver and blood and to explore their relationships with BT. Cirrhotic rats with ascites were induced by CCl4. We found that there were lower levels of total protein and albumin, lower albumin/globulin ratio, lower body weight and higher spleen weight and ascites volume in cirrhotic rats with than without BT. We found that BT may cause increase of Treg cells in the proximal small intestine and decrease of Th17 cells in the whole intestine and blood in cirrhotic rats. It may also aggravate the CCl4-induced decrease in Th1 cells in the whole intestine, liver, caecum, and blood and the CCl4-induced increase in Th17 cells in the liver and Tregs in the distal small intestine, colon, and liver. Our data suggest that BT may aggravate liver injury and decrease liver function via an interaction with CD4+ T Cells. The results of this study may be helpful for the development of new treatments for liver cirrhosis.

Delayed-type hypersensitivity (DTH) is a T-cell-mediated immune response that may be used for immunotoxicity testing in non-clinical species. However, in some cases DTH assays using T-dependent antigens may be confounded by the production of antibodies to the antigen. The authors have previously modified a DTH assay, initially validated in the mouse, for use in juvenile rats to assess the effect of immunosuppressive drugs on the developing rat immune system. The assay measures footpad swelling induced by subcutaneous footpad injection of Candida albicans (C. albicans) derived-chitosan in rats previously sensitized with C. albicans. Antibodies to chitosan are not produced in this model. However, considerable inter-animal variability inherent in the footpad swelling assay can make it difficult to precisely quantify the magnitude of the immune response and inhibition by immunosuppressants, particularly if complete suppression is not observed. This report describes the development of an ex vivo assay to assess DTH in rats using interferon (IFN)-γ production by splenocytes, obtained from rats sensitized with C. albicans, as the quantifiable measure of the DTH response. Adult and neonatal rats administered dexamethasone (DEX), a known immunosuppressant, exhibited immunosuppression as evidenced by a reduction in ex vivo IFNγ production from splenocytes challenged with C. albicans-derived chitosan. Current data indicate that the ex vivo based DTH assay is more sensitive than the conventional footpad swelling assay due to a lower background response and the ability to detect a response as early as post-natal day (PND) 12. The ex vivo based rat DTH assay offers a highly sensitive and quantitative alternative to the footpad swelling assay for the assessment of the immunotoxic potential of drugs. The increased sensitivity of the ex vivo DTH assay may be useful for identifying smaller changes in response to immunotoxic drugs, as well as detecting responses earlier in animal development.