Bullous pemphigoid is an autoimmune disease that attacks proteins in the basement membrane known variably as 230 and 180 kD (kiloDalton) proteins or Type XVII Collagen. These proteins are in the basement membrane and act as intrinsic parts of the hemidesmosome which tacks down the basal cell keratinocytes to the basement membrane. Once these proteins are attacked and lysed by the autoantibodies, they float up because they are no longer attached, and lymphatic fluid fills up the space underneath the floating sheets of keratinocytes, resulting in fluid-filled blisters.
If you look at the pic above, you see very tense blisters. The tense blisters are tense because they contain the entire epidermis on top of them. More important, you see the red, inflamed background. That red background is where the autoantibodies are attaching themselves to the hemidesmosomes and thus triggering the lytic reaction, and so THAT is the area where you want to do your biopsy for IF. What you will see on H and E is lots of eosinophils, some neutrophils, and the very beginnings of separation of the basement membrane from the basal layer.
As I have said before, it takes three hands to do an IF biopsy for this condition: One to hold the skin, one to hold the punch, and one to direct the biopsying hand away from the blisters and onto the inflamed skin.
For those of you who guessed contact, the info that he was getting worse should have steered you away from that. He should have gradually improved over the two weeks. For those of you who guessed bullous impetigo, I would have given you a better pic of the honey colored crusting. Also, the blisters would have been more flaccid.