TL1A and IL-18 synergy promotes GM-CSF-dependent thymic granulopoiesis in mice

Acute systemic inflammation critically alters the function of the immune system,often promoting myelopoiesis at the expense of lymphopoiesis.In the thymus,systemic inflammation results in acute thymic atrophy and,consequently,impaired T-lymphopoiesis.The mechanism by which systemic inflammation impacts the thymus beyond suppressing T-cell development is still unclear.Here,we describe how the synergism between TL1A and IL-18 suppresses T-lymphopoiesis to promote thymic myelopoiesis.The protein levels of these two cytokines were elevated in the thymus during viral-induced thymus atrophy infection with murine cytomegalovirus(MCMV)or pneumonia virus of mice(PVM).In vivo administration of TL1A and IL-18 induced acute thymic atrophy,while thymic neutrophils expanded.Fate mapping with Ms4a3-Cre mice demonstrated that thymic neutrophils emerge from thymic granulocyte-monocyte progenitors(GMPs),while Rag1-Cre fate mapping revealed a common developmental path with lymphocytes.These effects could be modeled ex vivo using neonatal thymic organ cultures(NTOCs),where TL1A and IL-18 synergistically enhanced neutrophil production and egress.NOTCH blockade by the LY411575 inhibitor increased the number of neutrophils in the culture,indicating that NOTCH restricted steady-state thymic granulopoiesis.To promote myelopoiesis,TL1A,and IL-18 synergistically increased GM-CSF levels in the NTOC,which was mainly produced by thymic ILC1s.In support,TL1A-and IL-18-induced granulopoiesis was completely prevented in NTOCs derived from Csf2rb-/-mice and by GM-CSFR antibody blockade,revealing that GM-CSF is the essential factor driving thymic granulopoiesis.Taken together,our findings reveal that TL1A and IL-18 synergism induce acute thymus atrophy while promoting extramedullary thymic granulopoiesis in a NOTCH and GM-CSF-controlled manner.

Priming with FLO8-deficient Candida albicans induces Th1-biased protective immunity against lethal polymicrobial sepsis

The morphological switch between yeast and hyphae of Candida albicans is essential for its interaction with the host defense system.However,the lack of understanding of host-pathogen interactions during C.albicans infection greatly hampers the development of effective immunotherapies.Here,we found that priming with the C.albicans FLO8-deficient(flo8)mutant,locked in yeast form,protected mice from subsequent lethal C.albicans infection.Deficiency of Dectin-2,a fungus-derivedα-mannan recognition receptor,completely blocked flo8 mutant-induced protection.Mechanistically,the flo8 mutant-induced Dectin-2/CARD9-mediated IL-10 production in DCs and macrophages to block thymus atrophy by inhibiting the C.albicans-induced apoptosis of thymic T cells,which facilitated the continuous output of naive T cells from the thymus to the spleen.Continuous recruitment of naive T cells to the spleen enhanced Th1-biased antifungal immune responses.Consequently,depletion of CD4^(+)T cells or blockade of IL-10 receptor function using specific antibodies in mice completely blocked the protective effects of flo8 mutant priming against C.albicans infection.Moreover,mannans exposed on the surface of the flo8 mutant were responsible for eliciting protective immunity by inhibiting the C.albicans-induced apoptosis of thymic T cells to sustain the number of naive T cells in the spleen.Importantly,priming with the flo8 mutant extensively protected mice from polymicrobial infection caused by cecal ligation and puncture(CLP)by enhancing Th1-biased immune responses.Together,our findings imply that targeting FLO8 in C.albicans elicits protective immune responses against polymicrobial infections and that mannans extracted from the flo8 mutant are potential immunotherapeutic candidate(s)for controlling infectious diseases.