Anti-BP180-type mucous membrane pemphigoid immunoglobulin G shows heterogeneity of internalization of BP180/collagen XVII into keratinocyte cytoplasm

The Role of Serology in the Diagnosis of Ocular Predominant Mucous Membrane Pemphigoid and the Search for an Ocular-Specific Autoantigen

Ocular predominant mucous membrane pemphigoid (oMMP) is a severe subtype of MMP that can lead to scarring and blindness. While conjunctival biopsy for direct immunofluorescence (DIF) is considered the gold standard for diagnosis, limited sensitivity results in a false-negative rate upwards of 40%. Likewise, it remains unclear to what extent a negative biopsy, whether false-negative or true-negative, results in a different prognosis, with patients previously termed "pseudopemphigoid" demonstrating comparable disease progression. Serologic testing allows for a less invasive means to demonstrate circulating autoantibodies against known autoantigens in pemphigoid diseases. Patients with MMP, particularly oMMP, however, typically demonstrate low titers of circulating autoantibodies, limiting the diagnostic utility of these tests. The autoantigen integrin β4 has been previously reported to be a specific marker of pure ocular MMP, while in the majority of patients with oMMP, the identified target antigens are BP180 (type XVII collagen) and laminin 332. Recent studies have, however, demonstrated inconsistent reactivity and specificity for integrin β4 as an ocular-specific marker in MMP. Herein, we review the role of serologic testing in the diagnosis and prognosis of oMMP, as well as the current understanding of autoantigens in oMMP.Abbreviations: BMZ - basement membrane zone, DIF - direct immunofluorescence, IIF - indirect immunofluorescence, MMP - mucous membrane pemphigoid, oMMP - ocular predominant mucous membrane pemphigoid.

Bullous Pemphigoid IgG Induces Cell Dysfunction and Enhances the Motility of Epidermal Keratinocytes via Rac1/Proteasome Activation

Bullous pemphigoid (BP) is an autoimmune disease characterized by the formation of blisters, in which autoantibodies mainly target type XVII collagen (ColXVII) expressed in basal keratinocytes. BP IgG is known to induce the internalization of ColXVII from the plasma membrane of keratinocytes through macropinocytosis. However, the cellular dynamics following ColXVII internalization have not been completely elucidated. BP IgG exerts a precise effect on cultured keratinocytes, and the morphological/functional changes in BP IgG-stimulated cells lead to the subepidermal blistering associated with BP pathogenesis. Based on the electron microscopy examination, BP IgG-stimulated cells exhibit alterations in the cell membrane structure and the accumulation of intracellular vesicles. These morphological changes in the BP IgG-stimulated cells are accompanied by dysfunctional mitochondria, increased production of reactive oxygen species, increased motility, and detachment. BP IgG triggers the cascade leading to metabolic impairments and stimulates cell migration in the treated keratinocytes. These cellular alterations are reversed by pharmacological inhibitors of Rac1 or the proteasome pathway, suggesting that Rac1 and proteasome activation are involved in the effects of BP IgG on cultured keratinocytes. Our study highlights the role of keratinocyte kinetics in the direct functions of IgG in patients with BP.

The Diagnosis and Blistering Mechanisms of Mucous Membrane Pemphigoid

Mucous membrane pemphigoid (MMP) is a mucous membrane-dominated autoimmune subepithelial blistering disease that is caused by autoantibodies against various autoantigens in basement membrane zone (BMZ) proteins, including collagen XVII (COL17). Clinicians face diagnostic problems in detecting circulating antibodies and targeted antigens in MMP. The diagnostic difficulties are mainly attributed to the low titers of MMP autoantibodies in sera and to heterogeneous autoantigens. Additionally, no unanimous diagnostic criteria have been drawn for MMP, which can result in delayed diagnoses or misdiagnoses. This review aims to integrate and present currently available data to clarify diagnostic strategies and to present diagnostic criteria for MMP. The ultimate blistering mechanism in MMP has not been elucidated, and such mechanism is especially obscure in COL17-type MMP. In bullous pemphigoid (BP), which is the most common autoimmune subepidermal blistering disease, some patients show oral lesion as well as predominant skin lesions. However, there is no fundamental explanation for the onset of oral lesions in BP. This article summarizes innovative research perspectives on the pathogenesis of oral lesions in pemphigoid. Finally, we propose a potential pathogenesis for COL17-type MMP.