Congenital Deficiency of Conventional Dendritic Cells Promotes the Development of Atopic Dermatitis-Like Inflammation

Abstract

Atopic dermatitis (AD) is a common pruritic inflammatory skin disease characterized by impaired epidermal barrier function and dysregulation of Thelper-2 (T_H2)-biased immune responses. While the lineage of conventional dendritic cells (cDCs) are implicated to play decisive roles in T-cell immune responses, their requirement for the development of AD remains elusive. Here, we describe the impact of the constitutive loss of cDCs on the progression of AD-like inflammation by using binary transgenic (Tg) mice that constitutively lacked CD11c^hi cDCs. Unexpectedly, the congenital deficiency of cDCs not only exacerbates the pathogenesis of AD-like inflammation but also elicits immune abnormalities with the increased composition and function of granulocytes and group 2 innate lymphoid cells (ILC2) as well as B cells possibly mediated through the breakdown of the Fms-related tyrosine kinase 3 ligand (Flt3L)-mediated homeostatic feedback loop. Furthermore, the constitutive loss of cDCs accelerates skin colonization of Staphylococcus aureus (S. aureus), that associated with disease flare. Thus, cDCs maintains immune homeostasis to prevent the occurrence of immune abnormalities to maintain the functional skin barrier for mitigating AD flare.

Keywords: atopic dermatitis; dendritic cells; homeostatic feedback loop; immune homeostasis; type 2 immune responses.

Figure 1

Constitutive loss of cDCs aggravates the development of AD-like inflammation. (A, B) WT mice and ΔCD11c^hi cDC mice (n = 14 per group) were treated topically with MC903 on the left ear skin. (A) Ear thickness was evaluated for 16 days. Data were obtained from fourteen individual samples in a single experiment. (B) Representative pictures of ear skin lesions at days 0 (None) and 16 (MC903). (C, D) Representative hematoxylin and eosin (H&E) sections (magnification; 200x) of ear skin (C), and epidermal thickness (D) was evaluated at days 0 (None) and 16 (MC903). Bars indicate 100 μm. Data were obtained from five individual samples in a single experiment. (E, F) Representative toluidine blue sections (magnification; 200x) for detecting MCs of ear skin (E), and the quantification of MCs of the skin (F) at days 0 (None) and 16 (MC903). Bars indicate 100 μm. HPF, high performance field. Data were obtained from three individual samples in a single experiment. *P < .05, **P < .01 compared with WT mice by two-sided paired student t-test. All data are representative of at least 3 independent experiments.

Figure 2

Constitutive loss of cDCs accelerates the AD-associated abnormal immune cell composition. The frequency of leukocytes in Spl (A), EDLNs (B), ear skin (C) obtained from WT mice and ΔCD11c^hi cDC mice (n = 10 per group) at 16 days after topical application with MC903. Data are obtained from ten individual samples in a single experiment. *P < .05, **P < .01 compared with WT mice by two-sided paired student t-test. All data are representative of at least 3 independent experiments.

Figure 3

Constitutive loss of cDCs enhances the AD-associated inflammation. (A) Serum production of cytokines in WT mice and ΔCD11c^hi cDC mice (n = 4 per group) at 16 days after topical application with MC903. Data are obtained from four individual samples in a single experiment. (B) Transcriptional expression of inflammation- and epithelium-related molecules in ear skin obtained from WT mice and ΔCD11c^hi cDC mice (n = 9 per group) at 16 days after topical application with MC903. Data are obtained from nine individual samples in a single experiment. *P < .05, **P < .01 compared with WT mice by two-sided paired student t-test. All data are representative of at least 3 independent experiments.

Figure 4

Constitutive loss of cDCs reciprocally controls the composition of CD4⁺ T_eff cells and ILCs during onset of AD-like inflammation. The frequency of the subsets of T cells (A) and ILCs (B) in EDLNs obtained from WT mice and ΔCD11c^hi cDC mice (n = 6 per group) at 16 days after topical application with MC903. Data are obtained from six individual samples in a single experiment. *P < .05, **P < .01 compared with WT mice by two-sided paired student t-test. All data are representative of at least 3 independent experiments.

Figure 5

Constitutive loss of cDCs affects the AD-associated B-cell responses in during onset of AD-like inflammation. (A) Serum production of IgG and IgE in WT mice and ΔCD11c^hi cDC mice (n = 8 per group) at 16 days after topical application with MC903. (B–E) The frequency of the subsets of IgM⁺ B cells, $\text{Ig}{\text{G}}_1^{+}$ B cells, and IgE⁺ B cells in whole (B, C) and GC (D, E) of Spl (B, D) and EDLNs (C, E) obtained from WT mice and ΔCD11c^hi cDC mice (n = 8 per group) at 16 days after topical application with MC903. (F) The frequency of the subsets of IgM⁺ plasma cells, $\text{Ig}{\text{G}}_1^{+}$ plasma cells, and IgE⁺ plasma cells of BM obtained from WT mice and ΔCD11c^hi cDC mice (n = 8 per group) at 16 days after topical application with MC903. Data are obtained from eight individual samples in a single experiment. *P < .05, **P < .01 compared with WT mice by two-sided paired student t-test. All data are representative of at least 3 independent experiments.

Figure 6

Constitutive loss of cDCs accelerates the colonization of S. aureus and the disruption of barrier function in eczematous skin. (A, B) Quantification of S. aureus cultured from the homogenates of ear skin of WT mice and ΔCD11c^hi cDC mice (n = 7 per group) at days 0 and 16 after topical application with MC903. (A) Representative pictures of Mannitol salt agar with egg yolk plates at days 0 (None) and 16 (MC903). (B) CFU of S. aureus at days 0 (None) and 16 (MC903) after topical application with MC903. **P <.01 compared with WT mice by two-sided paired student t-test. (C, D) WT mice (C) and ΔCD11c^hi cDC mice (D) (n = 6 per group) were treated topically with MC903 in combination with or without antibiotic ointment or petrolatum on the left ear skin. Ear thickness was evaluated for 16 days. Data are obtained from seven individual samples in a single experiment. *P < .05, **P < .01 compared with MC903-treated group or among groups. All data are representative of at least 3 independent experiments by two-way ANOVA.