Neutrophils are classically defined as terminally differentiated, short-lived cells; however, neutrophils can be long-lived with phenotypic plasticity. During inflammation, a subset of neutrophils transdifferentiate into a population called neutrophil-DC hybrids (PMN-DCs) having properties of both neutrophils and dendritic cells. While these cells ubiquitously appear during inflammation, the role of PMN-DCs in disease remains poorly understood. We observed the differentiation of PMN-DCs in pre-clinical murine models of fungal infection: blastomycosis, aspergillosis and candidiasis. Using reporter strains of fungal viability, we found that PMN-DCs associate with fungal cells and kill them more efficiently than undifferentiated canonical neutrophils. During pulmonary blastomycosis, PMN-DCs comprised less than 1% of leukocytes yet contributed up to 15% of the fungal killing. PMN-DCs displayed higher expression of pattern recognition receptors, greater phagocytosis, and heightened production of reactive oxygen species compared to canonical neutrophils. PMN-DCs also displayed prominent NETosis. To further study PMN-DC function, we exploited a granulocyte/macrophage progenitor (GMP) cell line, generated PMN-DCs to over 90% purity, and used them for adoptive transfer and antigen presentation studies. Adoptively transferred PMN-DCs from the GMP line enhanced protection against systemic infection in vivo. PMN-DCs pulsed with antigen activated fungal calnexin-specific transgenic T cells in vitro and in vivo, promoting the production of interferon-γ and interleukin-17 in these CD4+ T cells. Through direct fungal killing and induction of adaptive immunity, PMN-DCs are potent effectors of antifungal immunity and thereby represent innovative cell therapeutic targets in treating life-threatening fungal infections.

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When functioning properly, the immune system protects the body from foreign invaders with the help of T‐cells. An error in the formation of T‐cells in the thymus can lead to autoimmune diseases in which the T‐cells attack normal body tissues. When a T‐cell binds to an antigen, a signal transduction pathway is activated, forming a multimeric signaling complex known as the TCR signalosome. LCK, part of the signalosome, is a lymphocyte‐specific protein tyrosine kinase that phosphorylates a variety of proteins in order to activate the T‐cell receptor pathway. TCR stimulation also leads to the activation of LYP, a lymphoid tyrosine phosphatase that down regulates TCR signaling by removing phosphates from the signaling intermediates of the TCR signalosome. LYP also dephosphorylates Y394 of LCK, thus inactivating the kinase and inhibiting TCR signaling. The LYP R620W mutation prevents LYP from binding to the signalosome, resulting in a gain‐of‐function, leading to increased inhibition of TCR signaling. The LYP R620W mutation has been linked to a wide spectrum of human diseases, including a decreased risk in Crohn’s disease and increased risk to rheumatoid arthritis, and possible links to non‐autoimmune disorders such as cardiovascular disease. The Marshfield SMART (Students Modeling A Research Topic) Team modeled the mutated protein LYP R620W using 3D technology. Grant Funding Source: Supported by grants from NIH‐CTSA and NIH‐SEPA.

Allergic contact dermatitis (ACD) is an important diagnosis to consider in patients with dermatitis following specific exposures. Classically, ACD from persulfates is associated with hair‐bleaching products and spa water/swimming pool exposure and is most commonly reported in adult men. We report a case of ACD to potassium peroxymonopersulfate (PPMS), a common pool “shocking” chemical, in a 7‐year‐old boy presenting with recurrent and diffuse dermatitis triggered by swimming pool exposure.

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Neutrophils are typically considered short-lived and terminally differentiated. However, recent studies have identified a poorly understood neutrophil subset that can differentiate into dendritic cells and become long-lasting “hybrids” of neutrophils and dendritic cells. These neutrophil-dendritic cells (PMN-DCs) maintain the functions of canonical neutrophils while gaining antigen-presenting properties of dendritic cells, enabling them to contribute to both innate and adaptive immunity. Although PMN-DCs have been characterized in various inflammatory conditions, the cues that drive their development are not fully understood. Granulocyte macrophage colony-stimulating factor (GM-CSF) has previously been implicated as an important signal for PMN-DC development in studies of murine and human neutrophils. In vivo neutralization suggests that GM-CSF is sufficient but not necessary to drive PMN-DC differentiation. To determine the requirement of GM-CSF we have deleted GM-CSF receptor using CRISPR editing of a murine neutrophil progenitor cell line. We have tested other implicated cytokines in vitro, including IL-3, IL-4, TNF-α and IFN-γ, however these signals alone do not induce differentiation of PMN-DCs but can augment or blunt PMN-DC differentiation. Previous work shows that PMN-DCs are potent effectors of antifungal immunity through both direct killing and antigen presentation; understanding of the developmental signals that drive PMN-DC differentiation is essential for any future therapies targeting PMN-DCs.