Conventional DCs are a heterogeneous population that bridge the innate and adaptive immune systems. The lung DC population comprises CD103+XCR1+ DC1s and CD11b+ DC2s; their various combined functions cover the whole spectrum of immune responses needed to maintain homeostasis. Here, we report that in vivo exposure to LPS leads to profound alterations in the proportions of CD103+XCR1+ DCs in the lung. Using ex vivo LPS and TNF stimulations of murine lung and spleen‐isolated DCs, we show that this is partly due to a direct downregulation of the GM‐CSF‐induced DC CD103 expression. Furthermore, we demonstrate that LPS‐induced systemic inflammation alters the transcriptional signature of DC precursors toward a lower capacity to differentiate into XCR1+ DCs. Also, we report that TNF prevents the capacity of pre‐DCs to express CD103 upon maturation. Overall, our results indicate that exposure to LPS directly impacts the capacity of pre‐DCs to differentiate into XCR1+ DCs, in addition to lowering their capacity to express CD103. This leads to decreased proportions of CD103+XCR1+ DCs in the lung, favoring CD11b+ DCs, which likely plays a role in the break in homeostasis following LPS exposure, and in determining the nature of the immune response to LPS.
Airway hyperresponsiveness (AHR), a major hallmark of asthma, results from alterations of contractile and noncontractile elements of airway reactivity. CD34 is a sialomucin that is expressed on various cells involved in asthma, such as eosinophils and airway smooth muscle precursors, highlighting its potential influence in AHR. To study the role of CD34 in regulating the contractile and noncontractile elements of AHR, AHR was induced by chronic exposure to house dust mite (HDM) antigen. To assess the role of CD34 on the contractile elements of AHR, airway reactivity and airway smooth muscle contractility in response to methacholine were measured. To assess CD34's role in regulating the noncontractile elements of AHR, a chimeric mouse model was used to determine the impact of CD34 expression on inflammatory versus microenvironmental cells in AHR development. Extracellular matrix production, mucus production, and mast cell degranulation were also measured. Whereas wild-type mice developed AHR in response to HDM, a loss of airway reactivity was observed in Cd34 mice 24 hours after the last exposure to HDM compared with naive controls. This was reversed when airway reactivity was measured 1 week after the last HDM exposure. Additionally, mast cell degranulation and mucus production were altered in the absence of CD34 expression. Importantly, simultaneous expression of CD34 on cells originating from the hematopoietic compartment and the microenvironment was needed for expression of this phenotype. These results provide evidence that CD34 is required for AHR and airway reactivity maintenance in the early days after an inflammatory episode in asthma.
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