This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Blistering disorders, Subject name: Dental
Direct immunofluorescence is positive in? 
Select and explain. 
A. Atopic dermatitis, B. Psoriasis vulgaris, C. Pemphigus vulgaris, D. Secondary syphilis
C: Pemphigus vulgaris
Answer: C: Pemphigus vulgaris 
Explanation: Direct immunofluorescence is positive in Pemphigus group of diorders. The diagnosis of pemphigus is confirmed by direct IF which shows IgG and often C3 deposited on the surface of keratinocytes throughout the epidermis in perilesional skin Direct immunofluorescence is also done for pemphigoid and dermatitis herpetiformis.