Role of the popliteal lymph node in infection with Mycobacterium marinum of the hind footpad of the mouse, and source of the cells that characterize the process.

We examined the possibility that the popliteal lymph node serves as the source of the lymphocytes that, together with macrophages, characterize the lesion produced by infection with Mycobacterium marinum in the hind footpad of the mouse. Naïve mice were partially protected against challenge with M. marinum in the hind footpad by intravenous infusion of lymphocytes harvested from the popliteal nodes of donor mice infected with M. marinum 7 days earlier. Lymphocytes harvested from the popliteal nodes of infected donors, labelled in vitro with 3H-uridine, and infused intravenously into naïve mice that were immediately challenged in the hind footpads with M. marinum, localized in the popliteal nodes of the recipient mice but not in the footpad lesions. Lymphocytes harvested from the spleens of naïve donors and labelled in vitro appeared to home to the popliteal node draining the M. marinum-infected footpad. Thus, the primary role of the popliteal lymph node appeared to be passive trapping of the lymphocytes brought to it by the circulation or afferent lymphatics. We then tried to locate the sources of both lymphocytes and macrophages that characterize the lesion. Temporary occlusion of the abdominal aorta prevented labelling by intravenously infused 3H-thymidine (3H-TdR) of the mononuclear cells of both footpad lesion and popliteal node. Temporary occlusion of the left common iliac artery during 3H-TdR infusion prevented immediate labelling on the ipsilateral side. After 24 and 48 h, however, small numbers of labelled lymphocytes were found in the left hind footpad lesion. Amputation of the right leg at the hip joint, but not right popliteal lymphadenectomy, performed immediately after re-establishment of patency of the left common iliac artery, prevented the late influx of labelled lymphocytes into the lesion of the left hind footpad. Thus, the chief source of both the lymphocytes and the macrophages of the footpad lesion appeared to be the lesion itself.