IgM Pemphigoid
Description
Figure S1. Clinical pictures, skin histopathologies, and further immunopathological characteristics of patients with IgM pemphigoid. Erythema and urticarial plaques on the right leg in patient 2 (row 1, left panel) and erythematous papules on the left lower leg in patient 3 (row 2, left panel). Histology of lesional skin biopsies showed mild spongiosis and an inflammatory infiltrate of lymphocytes and eosinophils in the upper dermis (H&E staining, 200x); patient 2 (row 1, middle panel) and patient 3 (row 2, middle panel). Direct immunofluorescence (IF) microscopy showed linear deposits of IgM at the dermal-epidermal junction (400x; patients 2 and 3, row 1 and 2, right panels). Indirect IF microscopy on human salt-split skin reveals circulating IgM antibodies labelling the roof of the artificial split in all three patients (200x; patients 1-3, row 3). By immunoblotting (IB) with recombinant BP180 NC16A, serum IgM reactivity is observed in patient 2 (row 4, left panel, lane 2, arrow) but not in patients 1 and 3 (row 4, left panel, lanes 1 and 3). IB with the recombinant BP180 ectodomain shows serum IgM antibodies in all patients (row 4, middle panel, lanes 1-3). By IB with a recombinant C-terminal stretch of BP180, IgM serum reactivity is found in all 3 patients (row 4, right panel, lanes 1-3). No IgM reactivity against the three recombinant BP180 fragments was observed in three normal human sera (row 4, all panels, lanes 4-6). Figure S2. Sera of patients with IgM pemphigoid do not induce dermal-epidermal separation in an ex vivo cryosection assay Six μm cryosections of normal human skin were incubated with sera from a patient with bullous pemphigoid (positive control, row 1, left panel), patients 1-3 (row 1, middle and right panel; row 2, left panel), and a healthy blood donor (row 2, middle panel). Subsequently, cryosections were incubated with leucocytes isolated from the peripheral blood of healthy volunteers. While the bullous pemphigoid serum induced dermal-epidermal separation (row 1, left panel, arrows), no splitting was observed using sera from patient 1-3 (row 1, middle and right panel; row 2 left panel) and the healthy blood donor (row 2, middle panel). H&E, 200x. Figure S3. Sera of patients with IgM pemphigoid induce internalization in an ex vivo Col17 internalization assay. HaCat cells were incubated with sera from a patient with bullous pemphigoid (positive control, row 1, left panel), patients 1-3 with IgM pemphigoid (row 1, middle and right panel; row 3, left panel), and a healthy blood donor (row 3, middle panel). While the bullous pemphigoid serum and serum of IgM pemphigoid induced internalization (row 2, all panels; row 4, left panel; arrows), no internalization was observed in the healthy blood donor (row 3, middle panel).