Response in the hindfoot pad and popliteal lymph node of C57BL mice to infection with Mycobacterium marinum.

C57BL mice inoculated in the hindfoot pads with 5 X 10(3) viable Mycobacterium marinum developed a localized disease process, characterized by swelling of the foot and increases in the number of acid-fast bacilli and colony forming units recovered. These changes became maximal 10 to 14 days after inoculation and then decreased in intensity. An acute inflammatory response appeared in the hindfoot pad during the first 24 h and increased in intensity during the next few days. By seven days after inoculation, the polymorphonuclear leukocytes had been largely replaced by lymphocytes and macrophages which led, during the next two weeks, to the extensive formation of granulomas. Epithelioid granulomas developed after at least 90% of the organisms had been killed. Simultaneously the popliteal lymph node increased greatly in size due to hyperplasia of the paracortical area, which contained a large number of pyroninophilic cells, and packing of sinusoids with small lymphocytes. Well-formed epithelioid granulomas containing acid-fast bacilli developed in the popliteal node. A small number of viable bacilli were found in both the hindfoot pad and the popliteal node 18 months after inoculation; this was accompanied by solid resistance to secondary challenge.