The correct answer is B. Type XVII collagen (BP180). 

Bullous pemphigoid (BP) is an IgG mediated autoimmune subepidermal blistering disorder. The autoantibodies are directed against the hemidesmosome, which helps to anchor basal keratinocytes to the basement membrane. In BP, the primary antigens are BP180 (type XVII collagen) and BP230. Blisters are formed due to the release of proteolytic enzymes that occur as a result of complement activation due to autoantibody binding to these components. C3 deposition along the basement membrane in particular leads to the recruitment of inflammatory immune cells. The use of salt-split skin testing provides additional evidence as the level of involvement within the basement membrane. The basement membrane is separated within the lamina lucida and divides the tissue into a roof (epidermis) and a floor (dermis). In BP, the hemidesmosomal antigens (BP180 and BP230) are involved and therefore the epidermal “roof” side will show linear IgG and C3 deposition.

Collagen VII is located beneath the lamina densa and would demonstrate floor pattern binding, consistent with epidermolysis bullosa acquisita rather than bullous pemphigoid. Laminin 332 is located on the dermal side (floor side) of the lamina lucida and is targeted in anti-laminin 332 mucous membrane pemphigoid.  Desmoglein 1 is a desmosomal cadherin involved in cell-cell adhesion within the epidermis and is implicated within intra-epidermal blistering disorders that would demonstrate a flaccid bullae. Integrin α6β4 is a hemidesmosomal integrin located closer to the dermal side, more characteristic of junctional epidermolysis bullosa rather than bullous pemphigoid.

References: Alikhan, A., & Hocker, T. L. (2023). Review of Dermatology E-Book. Elsevier Health Sciences.