Arginine vasopressin (AVP) made by hypothalamic neurons is released into the circulation to stimulate water resorption by the kidneys and restore water balance after blood loss. Patients who lack this antidiuretic hormone suffer from central diabetes insipidus. We observed that many of these patients were anemic and asked whether AVP might play a role in red blood cell (RBC) production. We found that all three AVP receptors are expressed in human and mouse hematopoietic stem and progenitor cells. The AVPR1B appears to play the most important role in regulating erythropoiesis in both human and mouse cells. AVP increases phosphorylation of signal transducer and activator of transcription 5, as erythropoietin (EPO) does. After sublethal irradiation, AVP-deficient Brattleboro rats showed delayed recovery of RBC numbers compared to control rats. In mouse models of anemia (induced by bleeding, irradiation, or increased destruction of circulating RBCs), AVP increased the number of circulating RBCs independently of EPO. In these models, AVP appears to jump-start peripheral blood cell replenishment until EPO can take over. We suggest that specific AVPR1B agonists might be used to induce fast RBC production after bleeding, drug toxicity, or chemotherapy.

Background aims: Bone marrow-derived mesenchymal stromal cells (MSCs) have been reported to suppress T-cell proliferation and used to alleviate the symptoms of graft-versus-host disease (GVHD). MSCs are a mixed cell population and at this time there are no tools to isolate the cells responsible for the T-cell suppression. We wanted to find a way to enhance the immunemodulatory actions of MSCs and tried varying the temperature at which they were cultured. Methods: We cultured human MSCs derived from healthy volunteers at different temperatures and tested their ability to switch macrophage character from pro-inflammatory to antiinflammatory (M1 type to M2 type). Using an enzyme-linked immunosorbent assay (ELISA), we showed that when MSCs are cultured at higher temperatures their ability to induce co-cultured macrophages to produce more interleukin-10, (IL-10) (an anti-inflammatory cytokine) and less tumor necrosis factor alpha, (TNFα) (a pro-inflammatory cytokine) is increased. We performed Western blots and immunocytochemistry to screen for changes that might underlie this effect. Results: We found that in hyperthermia the heat shock protein, HSF1, translocated into the nucleus of MSCs. It appears to induce the COX 2 /PGE 2 (Cyclooxygenase2/Prostaglandin E 2) pathway described earlier as a major mechanism of MSC-directed immune-suppression. Conclusion: Hyperthermia increases the efficacy of MSC-driven immune-suppression. We propose that changing the time of MSC administration to patients to mid-to-late afternoon when the body temperature is naturally highest might be beneficial. Warming the patient could also be considered.

Bone marrow derived stromal cells or mesenchymal stromal cells (BMSCs or MSCs, as we will call them in this work) are multipotent progenitor cells that can differentiate into osteoblasts, adipocytes and chondrocytes. In addition, MSCs have been shown to modulate the function of a variety of immune cells. Donor age has been shown to affect the regenerative potential, differentiation, proliferation and anti-inflammatory potency of MSCs; but the impact of donor age on their immunosuppressive activity is unknown. In this study, we evaluated the ability of MSCs derived from very young children and adults on T cell suppression and cytokine secretion by monocytes/macrophages. MSCs were obtained from extra digits of children between 10-21 months and adults between 28 and 64 years of age. We studied cell surface marker expression, doubling time, lineage differentiation potential, and immunosuppressive function of the MSCs. Young MSCs double more quickly and differentiate into bone and fat cells more efficiently than those from older donors. They also form more and dense colonies of fibroblasts (CFU-F). MSCs from both young and adult subjects suppressed T cell proliferation in a mitogen induced assay at 1:3 and 1:30 ratios. At a 1:30 ratio, however, MSCs from adults did not, but MSCs from infants did suppress T cell proliferation. In the mixed lymphocyte reaction assay, MSCs from infants produced similar levels of suppression at all three MSC/T cell ratios, but adult MSCs only inhibited T cell proliferation at a 1:3 ratio. Cytokine analyses of cocultures of MSCs and macrophages showed that both adult and young MSCs suppress TNF-α and induce IL-10 production in macrophage co-culture assay in a similar manner. Overall, this work shows that developing MSCs display a higher level of immunosuppression than mature MSCs.