Systemic inflammatory response syndrome triggered by blood-borne pathogens induces prolonged dendritic cell paralysis and immunosuppression.

Blood-borne pathogens can cause systemic inflammatory response syndrome (SIRS) followed by protracted, potentially lethal immunosuppression. The mechanisms responsible for impaired immunity post-SIRS remain unclear. We show that SIRS triggered by pathogen mimics or malaria infection leads to functional paralysis of conventional dendritic cells (cDCs). Paralysis affects several generations of cDCs and impairs immunity for 3-4 weeks. Paralyzed cDCs display distinct transcriptomic and phenotypic signatures and show impaired capacity to capture and present antigens in vivo. They also display altered cytokine production patterns upon stimulation. The paralysis program is not initiated in the bone marrow but during final cDC differentiation in peripheral tissues under the influence of local secondary signals that persist after resolution of SIRS. Vaccination with monoclonal antibodies that target cDC receptors or blockade of transforming growth factor ß partially overcomes paralysis and immunosuppression. This work provides insights into the mechanisms of paralysis and describes strategies to restore immunocompetence post-SIRS.

Leukemia inhibitory factor (LIF) modulates the development of dendritic cells in a dual manner.

Objective: Dendritic cells (DCs) are professional antigen presenting cells majorly modulated by various environmental factors. Leukemia inhibitory factor (LIF) is a pleiotropic cytokine from interleukin-6 family. Previous studies demonstrate that LIF is associated with several tolerogenic events; yet the exact effect of this cytokine on the generation and function of DCs was not explicitly identified. Materials and methods: To clarify the role of LIF in DCs development, immature DCs were differentiated from mouse bone marrow (BM) in a GM-CSF and IL-4 containing medium with or without LIF. Afterwards, in maturation process, the differentiated DCs were exposed to TNF-α in the presence or absence of LIF. Results: Immature DCs differentiated in the presence of LIF, proved a significant enhancement in the expression of MHCII, CD40, or CD86 molecules and in the antigen uptake function. LIF treatment of normal DCs while stimulating for maturation, caused a significant decrement in the expression of phenotypic markers as well as an increment in the antigen uptake function in comparison with TNF-α-only stimulated cells; however, the reduced ability for induction of allogenic T-cell proliferation proved no statistical significance. Conclusions: Our results can reflect a role for LIF in the generation and particularly maturation of DCs. It can be assumed that LIF rather modulates the maturation level, leading to the development of semi-mature and tolerogenic DCs. According to the high levels of LIF in immune-privileged sites like brain and uterine, it seems that the cytokine may account for the formation of local DCs that help the establishment of immunosuppressive environments.