cruzi infected mice, and IL-12 + IL-18-treated
mice. Data using specific inhibitors of MCP-1 and CCR2 further confirm this hypothesis. Interestingly, our data support the fact that IL-12 and IL-18 are the cytokines responsible for MCP-1 upregulation in the thymus, since we observed that in vitro recombinant IL-12 and IL-18 are able to significantly increase MCP-1 only in thymocytes from IL-12 + IL-18-cDNA treated mice, indicating that cells present in the thymi of mice exposed to systemic IL-12 + IL-18 but not in normal mice contain cells with the ability to produce this chemokine. Accordingly, further analysis demonstrates that thymic B cells and T cells CD44lo are the main producers of this chemokine in the thymus under these inflammatory conditions. Based on the data presented in this work, we propose a novel concept of peripheral lymphocyte Selleck INCB018424 recirculation during nonphysiological conditions. We demonstrate that in any potential situation where large amounts of IL-12
and IL-18 are produced buy LY2157299 as a consequence of an infectious/inflammatory process, the thymus cell number is reduced favoring the creation of new niches in this organ that facilitate peripheral B and T cells entrance to the thymus. Interestingly, this phenomenon occurs in the absence of any antigenic stimulation and seems to be part of bystander activation of certain peripheral mature B and T cells. The fact that systemic IL-12 and IL-18 expression is observed in numerous situations opens the possibility that this migratory events described here are also possible in a numerous type of pathological processes. At the present moment, why we are evaluating if the entrance of B and T cells is due to a mere opportunism of cells during a moment of large expansion of leukocytes or if it is a coordinated process that plays a role in thymus physiology. Moreover, evaluation of peripheral cell localization in the thymus could provide important information not only about the source of required factors peripheral B and T cells use to survive in the thymus but also about the role they
might have in different thymic processes such as negative and positive selection and differentiation of immature cells in this organ. Female or male C57BL/6 (B6) and OT-I mice (Jackson Laboratory) used in this study were 6–10 week old and were maintained under specific pathogen-free conditions. The experimental protocols were approved by the Institutional Animal Care and Use Committee (IACUC). Our animal facility obtained NIH animal welfare assurance (assurance number A5802-01, OLAW, NIH, USA). B6 mice were injected i.p. with LPS (055-B5, Sigma) in a sublethal concentration of 20 μg per mouse in 200 μL PBS once a day for 3 consecutive days. Trypanosoma cruzi trypomastigotes were maintained by serial passages in B6 mice. B6 mice were i.p. infected with 5 × 105 trypomastigotes from T. cruzi diluted in PBS.