Localization of antibody-forming cells in draining lymphoid organs during long-term maintenance of the antibody response.

Previous studies on the "spontaneous antibody response" have included in vitro steps and it is possible that the response is an in vitro artifact. The objective of the present study was to induce a spontaneous antibody response entirely in vivo and determine if the response is localized and if the magnitude of the response is related to the location of persisting antigen. Antigen was injected into the right hind footpads of mice, and lymph nodes on the right side were draining and lymph nodes on the left side were controls. Antibody-forming cells (AFCs) were enumerated in both draining and nondraining nodes 2 weeks, 2 months, and 1 year after secondary immunization. Four days prior to determining AFC number, the mice were severely bled to stimulate AFC production. Thousands of AFCs were found in the draining lymph nodes and the numbers were dramatic in nodes closest to the injection site that retain the most antigen. In contrast, the vast majority of nondraining nodes lacked any AFCs. One year after immunization, the response was almost exclusively in the popliteal node, draining the foot where antigen was administered a year earlier. These results are consistent with previous data on the spontaneous response and support the hypothesis that antigen retained on FDCs is essential in the maintenance of serum antibody levels.