Sequential Intramolecular Epitope Spreading of Humoral Responses to Human BPAG2 in a Transgenic Model

Abstract

Bullous pemphigoid (BP) is a subepidermal autoimmune disease characterized by a humoral response to an epidermal basement membrane (BM) component, BP antigen 2 (BPAG2). BP patients have IgG autoantibodies against an immunodominant BPAG2 extracellular domain termed NC16A as well as additional epitopes located both in the intracellular and extracellular domains (ICD and ECD, respectively) of this autoantigen. To study the evolution of humoral responses to BPAG2, sequential serum samples obtained from C57BL/6Ncr mice grafted with otherwise syngeneic skin from transgenic mice expressing human BPAG2 (hBPAG2) in epidermal BM were studied for IgG reactivity to seven ECD and ICD hBPAG2 epitopes. All grafted mice developed specific IgG against hBPAG2 ECD and ICD epitopes. In seven of eight mice, anti-hBPAG2 IgG was initially directed against ECD epitopes; in six mice, humoral responses subsequently targeted additional ECD and ICD BPAG2 epitopes. In contrast to IgG specific for ECD epitopes, IgG against ICD epitopes was present at lower levels, detectable for shorter periods, and non-complement fixing. Interestingly, the appearance of IgG directed against ICD epitopes correlated with the development of graft loss in this experimental model. These studies provide a comprehensive and prospective characterization of the evolution of humoral immune responses to hBPAG2 in vivo.

Demonstration of Epitope-Spreading Phenomena in Bullous Pemphigoid: Results of a Prospective Multicenter Study

“…IgG spreading from BP180 to BP230 might be attributed to the physical interaction between the NH2-terminal portions of BP230 and BP180 . These findings are in line with a previous study aimed at investigating the dynamics of the IgG response against human BP180 in a mouse model, in which transgenic mouse skin expressing human BP180 was grafted on wild-type animals (Di Zenzo et al, 2010). These mice developed first IgG against extracellular BP180 epitopes and thereafter IgG binding to intracellular epitopes.…”

“…In this model, IgG reactivity with extracellular epitopes preceded IgG recognition of intracellular domain. Appearance of IgG autoantibodies directed against intracellular epitopes correlated with the development of graft loss (Di Zenzo et al, 2010). A recent study that utilized a vast array of BP230 and BP180 peptides strongly suggested that BP patients have a specific IgG autoantibody profile, including IgG recognition of intracellular epitopes, which is detectable already at an early stage of the disease (Di Zenzo et al, 2008).…”

Pathogenicity of IgG subclass autoantibodies to type VII collagen: Induction of dermal–epidermal separation

“…It is highly likely that autoantibodies targeting both pathogenically relevant epitopes, resulting from intramolecular epitope spreading, could have additive pathogenic effects. Indeed, in mouse models of bullous pemphigoid, intramolecular epitope spreading is found to be highly correlated with clinical symptoms [47].…”

Antibodies to Pathogenic Epitopes on Type XVII Collagen Cause Skin Fragility in a Complement-Dependent and -Independent Manner

“…The importance of those autoantibodies has not been elucidated, although intramolecular epitope spreading has been advocated to explain the development of these autoantibodies (20)(21)(22).…”