Penetration, clearance and retention of antigen en route from the gingival sulcus to the draining lymph node of rats

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Abstract
We investigated the penetration and clearance of antigen in the rat gingiva and the antigen‐specific antibody response in the draining lymph nodes. Rats were primarily immunized into the alveolar submucosa with horseradish peroxidase (HRP) in complete Freund's adjuvant. Ultrastructural demonstration of antigen and specific antibody was performed by incubation of cryosections in an HRP solution, followed by peroxidase cytochemistry. Anti‐HRP antibody‐containing cells were observed in the draining lymph nodes from 2 to 9 weeks after immunization. The bulk of these cells were located in the medullary cords. The extracellular antibody and antibody‐containing cells were also found in germinal centers (GCs) from 3 to 9 wk, and 3 wk, respectively, after immunization. The results suggest that the specific antibody response was most enhanced 3 wk after primary immunization. Therefore, at this time we further challenged rats with the topical application of HRP to the gingival sulcus. The results showed that antigen penetrated through the junctional epithelium into the underlying connective tissue and from here was cleared by macrophages or via the lymphatics. In the draining lymph nodes, antigen first appeared in the subcapsular sinus and eventually became retained within GCs. Between 3 and 5 days, the GCs of challenged rats contained more mature‐type anti‐HRP antibody‐containing cells than those of non‐challenged rats. The sequence of events observed suggests that antigen challenge applied topically to the gingival sulcus can induce the active GC reaction in the draining lymph nodes of immunized rats.