Accumulation of plasma cells in inflamed sites: effects of antigen, nonspecific microbial activators, and chronic inflammation.

Plasma cells are common in chronically inflamed sites, including periodontal lesions. The aim of this study was to determine which factors contribute to this local accumulation of plasma cells. Specifically, we sought to evaluate the effects of specific antigen and nonspecific activators from an infectious agent associated with chronic inflammation (Fusobacterium nucleatum, an organism prominent in chronic periodontal lesions) and the effect of the chronic inflammation itself. Chronic inflammation (14 to 17 days) was induced in horseradish peroxidase (HRP)-immune rabbits by subcutaneous injection of 50 microliters of sterile alum in several sites in their backs. Controls included sites injected with saline or more acute sites examined after 3 days of alum inflammation. Sites were challenged with HRP (the antigen), sonicated F. nucleatum (the nonspecific activator), or both together to see whether F. nucleatum has an adjuvant effect. Three days after challenge, HRP-specific antibody-forming cells (AFC) were enumerated after peroxidase histochemistry. In noninflamed sites or sites with acute inflammation, virtually no HRP-specific AFC were evident. In contrast, chronic inflammation alone was sufficient to elicit a specific AFC response (congruent to 10 cells per mm2). Addition of either F. nucleatum or HRP to the chronic lesion about doubled the number of HRP-specific AFC. However, a dramatic 8- to 15-fold (80 to 150/mm2) increase was seen in chronically inflamed sites challenged with antigen and activator together. Interestingly, the activator did not have this adjuvant effect in the acute sites or in normal skin. In short, accumulation of plasma cells in inflamed sites is promoted by chronic inflammation, activators of microbial origin, and specific antigen. This milieu can be expected to develop in some periodontal lesions and could help explain why gingival crevicular fluid from some sites may contain extraordinary levels of locally produced specific antibodies for certain antigens.