Immunohistochemical studies of the acne-like inflammatory model

The acne-like inflammatory model was produced in the ears of male Sprague-Dawley rats by subcutaneous injection of 140 micrograms of heat killed Propionibacterium acnes (P. acnes). Ear thickness was measured as an index of inflammatory strength, using a micro indicator once every day for the first week, then every other day until the 35th day. Animals were sacrificed and ears were excised for histological study. The tissue was stained with Hematoxylin and Eosin to investigate the state of inflammation. At the same time, P. acnes was stained specifically by enzyme labelled antibody to study the localization of the injected bacteria body. When thickness of rat ears was measured, more than a doubling of control ear was observed with maximum swelling on the second day. The ear thickness decreased to 1.5 times control levels at 5th day, then remained with no change for 35 days. Histological study revealed remarkable inflammatory infiltration of lymphocytes and neutrophils at the swelling site. Polynucleocyte was major infiltrated cells until 24 hours, and then mononucleocyte was principal after 24 hours. In the tissue excised at 6 hours after injection, a temporary characteristic infiltration of eosinophils was observed. When the tissue at 35th day was stained by enzyme labelled antibody, it revealed that the antigen of P. acnes existed among the cells at the site of infiltration and in mononucleocytes. This inflammatory model is considered to be a valuable experimental animal model for acne vulagaris with granulomatous inflammation.