Structural Changes of Cutaneous Immune Cells in Patients With Type 1 Diabetes and Their Relationship With Diabetic Polyneuropathy

Abstract

Background and objectives: Diabetic polyneuropathy (DPN) is a complication of diabetes characterized by pain or lack of peripheral sensation, but the underlying mechanisms are not yet fully understood. Recent evidence showed increased cutaneous macrophage infiltration in patients with type 2 diabetes and painful DPN, and this study aimed to understand whether the same applies to type 1 diabetes.

Methods: The study included 104 participants: 26 healthy controls and 78 participants with type 1 diabetes (participants without DPN [n = 24], participants with painless DPN [n = 29], and participants with painful DPN [n = 25]). Two immune cells, dermal IBA1⁺ macrophages and epidermal Langerhans cells (LCs, CD207⁺), were visualized and quantified using immunohistological labeling and stereological counting methods on skin biopsies from the participants. The IBA1⁺ macrophage infiltration, LC number density, LC soma cross-sectional area, and LC processes were measured in this study.

Results: Significant difference in IBA1⁺ macrophage expression was seen between the groups (p = 0.003), with lower expression of IBA1 in participants with DPN. No differences in LC morphologies (LC number density, soma cross-sectional area, and process level) were found between the groups (all p > 0.05). In addition, IBA1⁺ macrophages, but not LCs, correlated with intraepidermal nerve fiber density, Michigan neuropathy symptom inventory, (questionnaire and total score), severity of neuropathy as assessed by the Toronto clinical neuropathy score, and vibration detection threshold in the whole study cohort.

Discussion: This study showed expressional differences of cutaneous IBA1⁺ macrophages but not LC in participants with type 1 diabetes-induced DPN compared with those in controls. The study suggests that a reduction in macrophages may play a role in the development and progression of autoimmune-induced diabetic neuropathy.

Figure 1. Immunofluorescent Labeling and Quantification of IBA1⁺ Macrophages in Human Skin Sections

(A) Representative images of different expression levels of IBA1⁺ macrophages in skin sections. (B) The quantification of IBA1 area fraction in dermis. Enclosed area by yellow dotted line: the region of interest (dermis that was 300 μm below epidermis-dermis border); T1D = type 1 diabetes without diabetic polyneuropathy; T1DPN = type 1 diabetes with painless diabetic polyneuropathy; P-T1DPN = type 1 diabetes with painful diabetic polyneuropathy.

Figure 2. Quantification of Cutaneous Langerhans Cell Morphologies

(A) Representative image of Langerhans cells in healthy human epidermis. (B) Representative structures of 4 Langerhans cell process levels. (C) Representative images of Langerhans cell soma cross-sectional area estimation. (D) The quantification of Langerhans cell number density in epidermis. (E) The quantification of Langerhans cell soma cross-sectional area in epidermis. (F) The quantification of Langerhans cell process levels in epidermis. LC = Langerhans cell; T1D = type 1 diabetes without diabetic polyneuropathy; T1DPN = type 1 diabetes with painless diabetic polyneuropathy; P-T1DPN = type 1 diabetes with painful diabetic polyneuropathy.

Figure 3. Correlations of Immune Cell Quantifications in all Participants

(A–C) Correlations between IBA1 area fraction and LC number density (A), LC soma cross-sectional area (B), and LC process level (C). (D–E) Correlations between 3 LC quantifications: (D) correlation between LC number density and LC process level (E) correlation between LC number density and LC soma cross-sectional area; and (F) correlation between LC process level and LC soma cross-sectional area. LC_density = LC number density; LC_soma = Langerhans cell soma cross-sectional area; LC_process = Langerhans cell process level.

Figure 4. Correlations Between IBA1 Area Fraction and Neuropathy Measurements

(A) Correlation between IBA1 area fraction and intraepidermal nerve fiber density (IENFD). (B) Correlation between IBA1 area fraction and Michigan Neuropathy Screening Instrument Questionnaire (MNSI-Q). (C) Correlation between IBA1 area fraction and Michigan Neuropathy Screening Instrument total score (MNSI total score). (D) Correlation between IBA1 area fraction and Toronto Clinical Neuropathy score (TCNS score). (E) Correlation between IBA1 area fraction and vibration test (Biothesiometer). (F) Correlation between IBA1 area fraction and HbA1c.