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The immunopathogenesis of psoriasis, a common chronic inflammatory disease of the skin, is incompletely understood. Here we demonstrate, using a combination of single cell and spatial RNA sequencing, IL-36 dependent amplification of IL-17A and TNF inflammatory responses in the absence of neutrophil proteases, which primarily occur within the supraspinous layer of the psoriatic epidermis. We further show that a subset of SFRP2+ fibroblasts in psoriasis contribute to amplification of the immune network through transition to a pro-inflammatory state. The SFRP2+ fibroblast communication network involves production of CCL13, CCL19 and CXCL12, connected by ligand-receptor interactions to other spatially proximate cell types: CCR2+ myeloid cells, CCR7+ LAMP3+ dendritic cells, and CXCR4 expressed on both CD8+ Tc17 cells and keratinocytes, respectively. The SFRP2+ fibroblasts also express cathepsin S, further amplifying inflammatory responses by activating IL-36G in keratinocytes. These data provide an in-depth view of psoriasis pathogenesis, which expands our understanding of the critical cellular participants to include inflammatory fibroblasts and their cellular interactions.

The induction of proinflammatory T cells by dendritic cell (DC) subtypes is critical for antitumor responses and effective immune checkpoint blockade (ICB) therapy. Here, we show that human CD1c+CD5+ DCs are reduced in melanoma-affected lymph nodes, with CD5 expression on DCs correlating with patient survival. Activating CD5 on DCs enhanced T cell priming and improved survival after ICB therapy. CD5+ DC numbers increased during ICB therapy, and low interleukin-6 (IL-6) concentrations promoted their de novo differentiation. Mechanistically, CD5 expression by DCs was required to generate optimally protective CD5hi T helper and CD8+ T cells; further, deletion of CD5 from T cells dampened tumor elimination in response to ICB therapy in vivo. Thus, CD5+ DCs are an essential component of optimal ICB therapy.

Acne affects 1 in 10 people globally, often resulting in disfigurement. The disease involves excess production of lipids, particularly squalene, increased growth of Cutibacterium acnes, and a host inflammatory response with foamy macrophages. By combining single-cell and spatial RNA sequencing as well as ultrahigh-resolution Seq-Scope analyses of early acne lesions on back skin, we identified TREM2 macrophages expressing lipid metabolism and proinflammatory gene programs in proximity to hair follicle epithelium expressing squalene epoxidase. We established that the addition of squalene induced differentiation of TREM2 macrophages in vitro, which were unable to kill C. acnes. The addition of squalene to macrophages inhibited induction of oxidative enzymes and scavenged oxygen free radicals, providing an explanation for the efficacy of topical benzoyl peroxide in the clinical treatment of acne. The present work has elucidated the mechanisms by which TREM2 macrophages and unsaturated lipids, similar to their involvement in atherosclerosis, may contribute to the pathogenesis of acne.

Granulomas are complex cellular structures composed predominantly of macrophages and lymphocytes that function to contain and kill invading pathogens. Here, we investigated the single-cell phenotypes associated with antimicrobial responses in human leprosy granulomas by applying single-cell and spatial sequencing to leprosy biopsy specimens. We focused on reversal reactions (RRs), a dynamic process whereby some patients with disseminated lepromatous leprosy (L-lep) transition toward self-limiting tuberculoid leprosy (T-lep), mounting effective antimicrobial responses. We identified a set of genes encoding proteins involved in antimicrobial responses that are differentially expressed in RR versus L-lep lesions and regulated by interferon-γ and interleukin-1β. By integrating the spatial coordinates of the key cell types and antimicrobial gene expression in RR and T-lep lesions, we constructed a map revealing the organized architecture of granulomas depicting compositional and functional layers by which macrophages, T cells, keratinocytes and fibroblasts can each contribute to the antimicrobial response.

Langerhans cells (LCs) reside in the epidermis where they are poised to mount an antimicrobial response against microbial pathogens invading from the outside environment. To elucidate potential pathways by which LCs contribute to host defense, we mined published LC transcriptomes deposited in GEO and the scientific literature for genes that participate in antimicrobial responses. Overall, we identified 31 genes in LCs that encode proteins that contribute to antimicrobial activity, ten of which were cross-validated in at least two separate experiments. Seven of these ten antimicrobial genes encode chemokines, CCL1, CCL17, CCL19, CCL2, CCL22, CXCL14 and CXCL2, which mediate both antimicrobial and inflammatory responses. Of these, CCL22 was detected in seven of nine transcriptomes and by PCR in cultured LCs. Overall, the antimicrobial genes identified in LCs encode proteins with broad antibacterial activity, including against Staphylococcus aureus, which is the leading cause of skin infections. Thus, this study illustrates that LCs, consistent with their anatomical location, are programmed to mount an antimicrobial response against invading pathogens in skin.

Human CD8+ cytotoxic T lymphocytes (CTLs) contribute to antimicrobial defense against intracellular pathogens through secretion of cytotoxic granule proteins granzyme B, perforin, and granulysin. However, CTLs are heterogeneous in the expression of these proteins, and the subset(s) responsible for antimicrobial activity is unclear. Studying human leprosy, we found that the subset of CTLs coexpressing all three cytotoxic molecules is increased in the resistant form of the disease, can be expanded by interleukin-15 (IL-15), and is differentiated from naïve CD8+ T cells by Langerhans cells. RNA sequencing analysis identified that these CTLs express a gene signature that includes an array of surface receptors typically expressed by natural killer (NK) cells. We determined that CD8+ CTLs expressing granzyme B, perforin, and granulysin, as well as the activating NK receptor NKG2C, represent a population of "antimicrobial CTLs" (amCTLs) capable of T cell receptor (TCR)-dependent and TCR-independent release of cytotoxic granule proteins that mediate antimicrobial activity.

Human Langerhans cells (LCs) are highly efficient at priming cytolytic CD8+ T cells compared with dermal CD14+ dendritic cells (DCs). Here we show that dermal CD141 DCs instead prime a fraction of naïve CD8+ I cells into cells sharing the properties of type 2 cytokinesecreting CD8+ T cells (1C2). Differential expression of the CDSantagonist receptors on dermal CD14+ DCs, the Ig-like transcript (ILl) inhibitory receptors, explains the difference between the two types of DCs. Inhibition of CD8 function on LC5 inhibited cytotoxic T lymphocytes (CRs) and enhanced 1C2 generation. In addition, blocking ILT2 or ILT4 on dermal CD14+ DCs enhanced the generation of CTLs and inhibited TC2 cytokine production. Lastly, addition of soluble ILT2 and 1L14 receptors inhibited CR priming by LCs. Thus, ILT receptor expression explains the polarization of CD8+ 1-cell responses by LCs vs. dermal CD14+ DCs. [ABSTRACT FROM AUTHOR]

Summary: Little is known about the functional differences between the human skin myeloid dendritic cell (DC) subsets, epidermal CD207+ Langerhans cells (LCs) and dermal CD14+ DCs. We showed that CD14+ DCs primed CD4+ T cells into cells that induce naive B cells to switch isotype and become plasma cells. In contrast, LCs preferentially induced the differentiation of CD4+ T cells secreting T helper 2 (Th2) cell cytokines and were efficient at priming and crosspriming naive CD8+ T cells. A third DC population, CD14−CD207−CD1a+ DC, which resides in the dermis, could activate CD8+ T cells better than CD14+ DCs but less efficiently than LCs. Thus, the human skin displays three DC subsets, two of which, i.e., CD14+ DCs and LCs, display functional specializations, the preferential activation of humoral and cellular immunity, respectively. [Copyright &y& Elsevier]

We recently reported that human epidermal Langerhans cells (LCs) are more efficient than dermal CD14+ DCs at priming naive CD8+ T cells into potent CTLs. We hypothesized that distinctive dendritic cell (DC) cytokine expression profiles (ie, IL-15 produced by LCs and IL-10 expressed by dermal CD14+ DCs) might explain the observed functional difference. Blocking IL-15 during CD8+ T-cell priming reduced T-cell proliferation by ∼ 50%. These IL-15-deprived CD8+ T cells did not acquire the phenotype of effector memory cells. They secreted less IL-2 and IFN-&ggr; and expressed only low amounts of CD107a, granzymes and perforin, and reduced levels of the antiapoptotic protein Bcl-2. Confocal microscopy analysis showed that IL-15 is localized at the immunologic synapse of LCs and naive CD8+ T cells. Conversely, blocking IL-10 during cocul-tures of dermal CD14+ DCs and naive CD8+ T cells enhanced the generation of effector CTLs, whereas addition of IL-10 to cultures of LCs and naive CD8+ T cells inhibited their induction. TGF-&bgr;1 that is transcribed by dermal CD14+ DCs further enhanced the inhibitory effect of IL-10. Thus, the respective production of IL-15 and IL-10 explains the contrasting effects of LCs and dermal CD14+ DCs on CD8+ T-cell priming. [ABSTRACT FROM AUTHOR]

Genetic analysis of human inborn errors of immunity has defined the contribution of specific cell populations and molecular pathways in the host defense against infection. The STAT family of transcription factors orchestrate hematopoietic cell differentiation. Patients with de novo activating mutations of STAT3 present with multiorgan autoimmunity, lymphoproliferation, and recurrent infections. We conducted a detailed characterization of the blood monocyte and dendritic cell (DC) subsets in patients with gain-of-function (GOF) mutations across the gene. We found a selective deficiency in circulating nonclassical CD16 + and intermediate CD16 + CD14 + monocytes and a significant increase in the percentage of classical CD14 + monocytes. This suggests a role for STAT3 in the transition of classical CD14 + monocytes into the CD16 + nonclassical subset. Developmentally, ex vivo-isolated STAT3 GOF CD14 + monocytes fail to differentiate into CD1a + monocyte-derived DCs. Moreover, patients with STAT3 GOF mutations display reduced circulating CD34 + hematopoietic progenitors and frequency of myeloid DCs. Specifically, we observed a reduction in the CD141 + DC population, with no difference in the frequencies of CD1c + and plasmacytoid DCs. CD34 + hematopoietic progenitor cells from patients were found to differentiate into CD1c + DCs, but failed to differentiate into CD141 + DCs indicating an intrinsic role for STAT3 in this process. STAT3 GOF -differentiated DCs produced lower amounts of CCL22 than healthy DCs, which could further explain some of the patient pathological phenotypes. Thus, our findings provide evidence that, in humans, STAT3 serves to regulate development and differentiation of nonclassical CD16 + monocytes and a subset of myeloid DCs., (Copyright © 2021 by The American Association of Immunologists, Inc.)