Predominant Infiltration of M2a Macrophages in Genital Verruciform Xanthoma

Academic Background

Verruciform xanthoma (VX) is a rare benign verrucous tumor first reported by Sachs in 1903 and formally named by Shafer in 1971. This lesion primarily occurs in the genital area and oral mucosa of elderly individuals. Histopathologically, it is characterized by papillomatous hyperplasia of the epidermis and foam cell infiltration in the dermis. Despite years of research, the etiology of VX remains incompletely understood. Given the unique location of the lesions (genital area) and their verrucous appearance, some scholars have speculated an association with human papillomavirus (HPV) infection, but multiple studies have failed to confirm this hypothesis. As a result, researchers have begun exploring other potential causative factors, including local irritation, microbial infections, and the involvement of immune cells.

Macrophages are a crucial component of the immune system and can be classified into M1 and M2 types based on their function and phenotype. M1 macrophages are typically induced by pro-inflammatory cytokines (such as IL-1, IL-12, IL-17, and TNF-α) and participate in inflammatory responses, while M2 macrophages are induced by IL-4 and IL-13 and exhibit anti-inflammatory and tissue-repairing functions. M2 macrophages are further divided into three subgroups: M2a (involved in tissue remodeling), M2b (involved in immune regulation and tumor progression), and M2c (involved in apoptotic cell clearance). In recent years, the role of macrophages in skin diseases has gradually gained attention, but their specific behavior in VX remains unclear. To address this, the research team in this study used immunohistochemistry and immunofluorescence techniques to investigate the infiltration of M2a macrophages in VX lesions, providing new insights into the etiology of VX.

Source of the Paper

This paper was co-authored by Akira Miyazaki, Tomoki Taki, Shoichiro Mori, Motohito Yamada, and Masashi Akiyama from the Department of Dermatology at Nagoya University Graduate School of Medicine and Toyohashi Municipal Hospital in Japan. The paper was accepted on January 21, 2025, and published in the Journal of Dermatology. The study received funding from the Ministry of Health, Labour and Welfare of Japan, the Japan Society for the Promotion of Science (JSPS), and the Japan Science and Technology Agency (JST).

Research Process and Results

Subjects and Experimental Design

The study included three Japanese male patients aged 71, 89, and 73 years, all with genital verruciform xanthoma. The first patient had a 1.5 × 1 cm lesion on the scrotum with a 10-year history; the second patient also had a scrotal lesion measuring 7 mm; and the third patient had a 2 cm scrotal lesion with a 10-month history. Additionally, a female patient with xanthelasma palpebrarum of the eyelid was included as a control group.

The researchers conducted histopathological analysis and immunohistochemical staining on the lesion tissues to detect markers of different macrophage types. Specifically, they used the following markers: CD68 (pan-macrophage marker), CD80 (M1 macrophage marker), CD86 (M1/M2b macrophage marker), CD163 (M2a/M2c macrophage marker), DC-SIGN (M2a macrophage marker), and CCR2 (M2c macrophage marker). Furthermore, immunofluorescence double staining was used to verify the co-expression of DC-SIGN and CD163.

Experimental Results

1. Histopathological Analysis
   The lesion tissues of all three patients exhibited typical VX features, including papillomatous hyperplasia of the epidermis and significant foam cell infiltration in the dermis, as confirmed by hematoxylin and eosin (H&E) staining.

2. Immunohistochemical Staining

   • CD68 was strongly positive in all cases, indicating a large presence of macrophages in the lesions.
     
   • CD80 (M1 macrophage marker) was weakly positive in cases 1 and 2 but strongly positive in case 3.
     
   • CD86 was weakly positive in all cases.
     
   • CD163 (M2a/M2c macrophage marker) was strongly positive in all cases.
     
   • DC-SIGN (M2a macrophage marker) was strongly positive in cases 1 and 2 but weakly positive in case 3.
     
   • CCR2 was negative in all cases.

3. Immunofluorescence Double Staining
   Immunofluorescence double staining revealed significant overlap between DC-SIGN-positive and CD163-positive cells, suggesting that these cells were primarily M2a macrophages. Additionally, CD80 and CD163-positive cells existed independently in the lesions, with no co-expression observed.

4. Molecular Expression Analysis
   The researchers also detected the expression of IL-⁴⁄₁₃ and TSLP (thymic stromal lymphopoietin) in the lesion tissues, which may be related to M2 macrophage polarization. Furthermore, the expression of periostin (a protein associated with tissue remodeling) was significantly higher in the lesion tissues compared to healthy controls.

Analysis and Conclusion

The main finding of this study is that M2a macrophages predominate in genital verruciform xanthoma lesions, accompanied by a small number of M1 macrophages. This aligns with previous studies, suggesting that M2a macrophages may play a significant role in the pathogenesis of VX. In particular, the co-expression of DC-SIGN and CD163 further supports this view.

The researchers hypothesized that microbial or physical stimulation at the lesion site might activate pattern recognition receptors (PRRs), inducing the infiltration of M2a macrophages. Additionally, the scrotum, as a site prone to friction, may promote foam cell formation through the action of CD163 (a hemoglobin scavenger receptor). These findings provide new explanations for the etiology of VX and may offer clues for future therapeutic strategies.

Research Significance and Highlights

The scientific value of this study is reflected in the following aspects:
1. It is the first systematic revelation of the predominant infiltration of M2a macrophages in genital verruciform xanthoma, providing crucial insights into the immunopathological mechanisms of VX.
2. Through immunohistochemistry and immunofluorescence techniques, the distribution of different macrophage types in the lesions was clarified, laying the groundwork for future immunotherapy research.
3. The study proposed the potential roles of microbial and physical stimulation in the pathogenesis of VX, offering new research directions for exploring its etiology.

Other Valuable Information

This study was also funded by the Ministry of Health, Labour and Welfare of Japan, the Japan Society for the Promotion of Science, and the Japan Science and Technology Agency. The research team specifically acknowledged the support of the Engineering Department and Technical Center at Nagoya University Graduate School of Medicine. Furthermore, the study strictly adhered to the Declaration of Helsinki and received approval from the ethics committees of Nagoya University Hospital and Toyohashi Municipal Hospital.

Through this in-depth analysis, future research can further explore the role of macrophage polarization in skin diseases and provide new perspectives for the diagnosis and treatment of VX.