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Neutrophils are produced in the BM in a process called granulopoiesis, in which progenitor cells sequentially develop into mature neutrophils. During the developmental process, which is finely regulated by distinct transcription factors, neutrophils acquire the ability to exit the BM, properly distribute throughout the body, and migrate to infection sites. Previous studies have demonstrated that CD40 ligand (CD40L) influences hematopoiesis and granulopoiesis. Here, we investigate the effect of CD40L on neutrophil development and trafficking by performing functional and transcriptome analyses. We found that CD40L signaling plays an essential role in the early stages of neutrophil generation and development in the BM. Moreover, CD40L modulates transcriptional signatures, indicating that this molecule enables neutrophils to traffic throughout the body and to migrate in response to inflammatory signals. Thus, our study provides insights into the complex relationships between CD40L signaling and granulopoiesis, and it suggests a potentially novel and nonredundant role of CD40L signaling in neutrophil development and function.

Introduction: CD40 ligand (CD40L) deficiency or X-linked Hyper-IgM syndrome is a severe primary immunodeficiency caused by mutations in the CD40L gene. Despite currently available treatments, CD40L-deficient patients remain susceptible to life-threatening infections and have poor long term survival. Areas covered: Here, we discuss clinical and immunological characteristics of CD40L deficiency as well as current therapeutic strategies used for patient management. This review highlights that beyond B cell defects, patients' susceptibility to opportunistic pathogens might be due to impaired T cell and innate immune responses. In this context, we discuss how better knowledge of CD40L function and regulation may result in the development of new treatments. Expert opinion: Despite the introduction of hematopoietic stem-cell transplantation, immunoglobulin replacement, granulocyte colony-stimulating factor (G-CSF) administration, and prophylactic antibiotic therapies, life-threatening infections still cause high morbidity and mortality among CD40L-deficient patients. The reasons for this inadequate response to current therapies remains poorly understood, but recent reports suggest the involvement of CD40L-CD40 interaction in early stages of the innate immune system ontogeny. The development of novel gene therapeutic approaches and the use of redirected immunotherapies represent alternative treatment methods that could offer reduced morbidity and mortality rates for patients with CD40L deficiency.

Background: Patients with X-linked hyper-IgM syndrome caused by CD40 ligand (CD40L) deficiency often present with episodic, cyclic, or chronic neutropenia, suggesting abnormal neutrophil development in the absence of CD40L-CD40 interaction. However, even when not neutropenic and despite immunoglobulin replacement therapy, CD40L-deficient patients are susceptible to life-threatening infections caused by opportunistic pathogens, suggesting impaired phagocyte function and the need for novel therapeutic approaches., Objectives: We sought to analyze whether peripheral neutrophils from CD40L-deficient patients display functional defects and to explore the in vitro effects of recombinant human IFN-γ (rhIFN-γ) on neutrophil function., Methods: We investigated the microbicidal activity, respiratory burst, and transcriptome profile of neutrophils from CD40L-deficient patients. In addition, we evaluated whether the lack of CD40L in mice also affects neutrophil function., Results: Neutrophils from CD40L-deficient patients exhibited defective respiratory burst and microbicidal activity, which were improved in vitro by rhIFN-γ but not soluble CD40L. Moreover, neutrophils from patients showed reduced CD16 protein expression and a dysregulated transcriptome suggestive of impaired differentiation. Similar to CD40L-deficient patients, CD40L knockout mice were found to have impaired neutrophil responses. In parallel, we demonstrated that soluble CD40L induces the promyelocytic cell line HL-60 to proliferate and mature by regulating the expression of genes of the same Gene Ontology categories (eg, cell differentiation) when compared with those dysregulated in peripheral blood neutrophils from CD40L-deficient patients., Conclusion: Our data suggest a nonredundant role of CD40L-CD40 interaction in neutrophil development and function that could be improved in vitro by rhIFN-γ, indicating a potential novel therapeutic application for this cytokine., (Copyright © 2018 American Academy of Allergy, Asthma & Immunology. Published by Elsevier Inc. All rights reserved.)

Previously, we demonstrated that cell-cell communications via the CD40-CD154 pathway play a critical role in the induction of type 1 cytokine responses, including IL-12 and IFN-γ, which in turn greatly influence the response to Salmonella infections. Mice genetically deficient in the expression of CD154 exhibited markedly increased susceptibility to infection by an attenuated, double auxotrophic (aroA-aroD-) strain, designated BRD509, of Salmonella enterica Serovar Typhimurium. In the present study, we used a strain of Salmonella engineered to express murine IFN-γ, designated GIDIFN, in order to assess its potential to enhance the host's immune response in CD154-deficient animals. We demonstrate that infection of animals with GIDIFN results in markedly enhanced anti-bacterial response, as evidenced by the significant reduction in bacterial loads in target organs and decreased animal mortality. This was associated with a more robust proinflammatory cytokine response, including IL-6, IL-12, TNF-α and IFN-γ. In protection studies, GIDIFN strain was demonstrably superior than the BRD509 strain in affording protection against virulent Salmonella challenge in naïve CD154-/- mice. Interestingly, however, infection with GIDIFN failed to correct the isotype switching defect in CD154-/- mice, suggesting that the enhanced immunity triggered by GIDIFN strain occurs independently of humoral immune responses. These findings demonstrate that GIDIFN has immunopotentiating effects on the host's immune response and provide direct evidence for the utility of IFN-γ-expressing attenuated Salmonella in enhancement of immune responsiveness in immunodeficient hosts., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

CD40-CD154 interactions are of central importance in the induction of humoral and cellular immune responses. In the present study, CD154-deficient (CD154-/-) mice were used to assess the role of CD40-CD154 interactions in regulating the immune response to a systemic Salmonella infection. Compared with C57BL/6 (CD154+/+) controls, CD154-/- mice were hypersusceptible to infection by an attenuated strain of Salmonella enterica serovar Typhimurium (S. typhimurium), as evidenced by decreased survival rate and mean time to death, which correlated with increased bacterial burden and persistence in target organs. CD154-/- mice exhibited a defect both in the production of IL-12, IFN-gamma, and NO during the acute phase of the disease and in the generation of Salmonella-specific Ab responses and Ig isotype switching. Furthermore, when CD154-/- animals were administered a sublethal dose of attenuated S. typhimurium and subsequently challenged with a virulent homologous strain, all mice succumbed to an overwhelming infection. Similar treatment of CD154+/+ mice consistently resulted in > or =90% protection. The lack of protective immunity in CD154-/- mice correlated with a decreased T cell recall response to Salmonella Ags. Significant protection against virulent challenge was conferred to presensitized CD154-/- mice by transfer of serum or T cells from immunized CD154+/+ mice. For best protection, however, a combination of immune serum and T cells was required. We conclude that intercellular communications via the CD40-CD154 pathway play a critical role in the induction of type 1 cytokine responses, memory T cell generation, Ab formation, and protection against primary as well as secondary Salmonella infections.

Salmonella species include facultative intracellular pathogens which reside preferentially within cells of the host's reticulo-endothelial system. Resistance to Salmonella involves a collaboration between cells of the innate and adaptive immune systems, and protective immunity requires cell-mediated and humoral-immune responses. CD40-CD154 interactions are of central importance in the induction of cellular immune responses. In the present study, CD154-deficient (CD154(-/-)) mice were used to assess the role of CD40-CD154 interactions in immunity to Salmonella infection. Compared to C57BL/6 (CD154(+/+)) controls, CD154(-/-) mice were hypersusceptible to infection by an attenuated strain of Salmonella enterica serovar Typhimurium (S. typhimurium), as evidenced by a significantly decreased survival rate. CD154(-/-) mice exhibited a defect in the production of IFN-gamma and NO in the acute phase of the disease, which resulted in a failure to control bacterial replication. We conclude that intercellular communications via the CD40-CD154 pathway play a critical role in the induction type-1 cytokine responses and protection against primary infections with attenuated Salmonella.