Blisters on the skin (part of the dermatitis herpetiformis version of celiac disease) are an inflammatory result due to a deposition of anti-tTG antibodies in the skin. In fact, recent studies have demonstrated that IgA antibodies against epidermal transglutaminase 3 play an important role in the pathogenesis of dermatitis herpetiformis.
See Nakajima K. Recent advances in dermatitis herpetiformis. Clin Dev Immunol. 2012;2012:914162. doi: 10.1155/2012/914162. Epub 2012 Jul 2: http://www.ncbi.nlm.nih.gov/pubmed/22811741 June, 2013