IRF4 expression by lung dendritic cells drives acute but not Trm cell-dependent memory Th2 responses

IRF4-regulated transcriptional and functional heterogeneity of lung-resident CD11b+ cDC2 subsets during influenza virus infection

Lung-resident conventional dendritic cells (cDCs) coordinate immune responses to respiratory viruses in the respiratory tract or after migration to mediastinal lymph nodes (mLN). Migratory DCs include cDC1s (CD103+XCR1+CD24hi) expressing IRF8 or cDC2s (CD11b+SIRPα+CD24+) expressing IRF4. IRF4+ cDC2s are divided into a CD24hi subset that requires IRF4 for differentiation and a CD24int subset that is present in the absence of IRF4. During influenza A virus (IAV) infection of mice, we characterized the kinetics of cDC2 subset accumulation in the lung and mLN and their differences in IRF4-dependent gene expression and function. We found that the 2 IRF4-expressing cDC2 subsets upregulated CD86 to high levels, produced IL-12p40 and the chemokines CCL17 and CCL22, and were capable of acquiring antigen in vivo and activating antigen-specific CD8+ T cells. Notably, the CD11b+CD24int cDC2 subset expressed canonical cDC markers and transcription factors and expanded to high numbers in the lung and mLN by d 6 postinfection. Transcriptome analyses on d 5 postinfection revealed that the CD11b+CD24int cDC2 subset expressed both IRF4 and IRF8 and harbored an elevated IFN response signature compared to the CD11b+CD24hi subset. Analyses of mice lacking Irf4 in CD11c+ cells showed that IRF4 promoted the function of CD11b+CD24int cDC2s, including the capacity to migrate to mLN and to produce CCL17 and CCL22, consistent with their altered gene expression profile in the absence of IRF4. In sum, our data show that the 2 lung-resident CD11b+ cDC2 subsets present in naïve mice elaborated distinct and common functional responses regulated by IRF4 during IAV infection.

Lung-resident memory CD4+ T cells are dependent on Batf3

Tissue-resident memory cells contribute to allergen-induced inflammation and airway hyperresponsiveness, but relatively little is known of the cellular and molecular mechanisms underlying the accumulation of these cells in the lung. Here, we show that allergen-specific CD4+ resident memory T cells are virtually absent in lungs of mice lacking Batf3, a transcription factor required for the development of type 1 lung dendritic cells (cDC1). These animals become sensitized to inhaled allergens and display normal responses in a short-term house dust mite-dependent model of asthma. However, they have strongly reduced airway inflammation and weak airway hyperresponsiveness in a similar, but long-term model of asthma. Single-cell RNA sequencing revealed that Batf3-deficient mice lack a subset of lung-resident CD4+ T cells characterized by expression of the chemokine receptor-encoding gene, Cxcr6. Together, these data show that Batf3 promotes the development of CD4+ resident memory T cells and thus allergic responses to inhaled allergens.

How type-2 dendritic cells induce Th2 differentiation: Instruction, repression, or fostering T cell-T cell communication?

Allergic disease is caused by the activation of allergen-specific CD4+ type-2 T follicular helper cells (Tfh2) and T helper 2 (Th2) effector cells that secrete the cytokines IL-4, IL-5, IL-9, and IL-13 upon allergen encounter, thereby inducing IgE production by B cells and tissue inflammation. While it is accepted that the priming and differentiation of naïve CD4+ T cells into Th2 requires allergen presentation by type 2 dendritic cells (DC2s), the underlying signals remain unidentified. In this review we focus on the interaction between allergen-presenting DC2s and naïve CD4+ T cells in lymph node (LN), and the potential mechanisms by which DC2s might instruct Th2 differentiation. We outline recent advances in characterizing DC2 development and heterogeneity. We review mechanisms of allergen sensing and current proposed mechanisms of Th2 differentiation, with specific consideration of the role of DC2s and how they might contribute to each mechanism. Finally, we assess recent publications reporting a detailed analysis of DC-T cell interactions in LNs and how they support Th2 differentiation. Together, these studies are starting to shape our understanding of this key initial step of the allergic immune response.

Emerging roles of MITF as a crucial regulator of immunity

Microphthalmia-associated transcription factor (MITF), a basic helix-loop-helix leucine zipper transcription factor (bHLH-Zip), has been identified as a melanocyte-specific transcription factor and plays a critical role in melanocyte survival, differentiation, function, proliferation and pigmentation. Although numerous studies have explained the roles of MITF in melanocytes and in melanoma development, the function of MITF in the hematopoietic or immune system-beyond its function in melanin-producing cells-is not yet fully understood. However, there is convincing and increasing evidence suggesting that MITF may play multiple important roles in immune-related cells. Therefore, this review is focused on recent advances in elucidating novel functions of MITF in cancer progression and immune responses to cancer. In particular, we highlight the role of MITF as a central modulator in the regulation of immune responses, as elucidated in recent studies.

Catching Our Breath: Updates on the Role of Dendritic Cell Subsets in Asthma

Dendritic cells (DCs), as potent antigen presenting cells, are known to play a central role in the pathophysiology of asthma. The understanding of DC biology has evolved over the years to include multiple subsets of DCs with distinct functions in the initiation and maintenance of asthma. Furthermore, asthma is increasingly recognized as a heterogeneous disease with potentially diverse underlying mechanisms. The goal of this review is to summarize the role of DCs and the various subsets therein in the pathophysiology of asthma and highlight some of the crucial animal models shaping the field today. Potential future avenues of investigation to address existing gaps in knowledge are discussed.