I hope you found yesterday’s post on the direct immunofluorescence (DIF) test on skin biopsies helpful. Today, we will cover the indirect immunofluorescence (IIF) test. This IIF test is a way to find whether a patient’s blood contains antibodies. In the case of autoimmune blistering disorders such as pemphigus vulgaris, bullous pemphigoid or paraneoplastic pemphigoid, we are looking for autoimmune antibodies (autoantibodies) to one’s own skin.
Normal skin biopsies get sent for hematoxylin and eosin staining (or what we call H&E staining). However, for certain skin conditions, we do a special test. We take a skin or oral biopsy for direct immunofluorescence (DIF) examination. These conditions that we are looking for may include blistering diseases such as pemphigus vulgaris, pemphigus foliaceus or bullous foliaceus, or non-blistering diseases such as lupus or Henoch-Schonlein purpura where one is looking for a specific vasculitis (inflammation around blood vessels).
So how is the direct immunofluorescence (DIF) exam done? First, a biopsy of skin or the oral mucosa is taken. Next, it is sent to the pathology lab where the skin is cut into small slivers and mounted onto a glass slide. Antibodies which have fluorescent tags on them are then thrown into the mix with this tissue. These antibodies that the pathology lab adds to the tissue may recognize other antibodies (e.g. IgA, IgM, IgG) or other products such as C3 or fibrinogen. Because the pathology lab’s antibodies have fluorescent tags, the pathologist can then see whether the fluorescence forms a specific pattern. For instance, the fluorescence may be brightest around the vessels (e.g. as in Henoch-Schonlein purpura), between the epidermis and dermis at the basement membrane (e.g. as in bullous pemphigoid), or between the cells of the epidermis (e.g. as in pemphigus vulgaris). Even a test which is negative may be helpful, since the negative test sways us away from certain diagnoses such as the ones we had listed above. For instance, we’d expect a disease such as a genetic epidermolysis bullosa (EB) to have a negative DIF.
Hope that helps you interpret your pathology biopsy report. Stay tuned to future posts to learn how indirect immunofluorescence (IIF) differs from direct immunofluorescence!