Correlation between Histology, Immunology and Microbiology in Human Periapical lesions

Objective: Histologically, human periapical lesions are inflammatory lesions that vary from inflamed granulation tissue and fibrous connective tissue to epithelial lined cysts. Immune cells, including CD4 and CD8 T lymphocytes, macrophages, natural killer cells, plasma cells, and eosinophils have been identified within tissues taken from periapical lesions. Recently, we have also identified gdT lymphocytes in a large majority of periapical lesions. We have noted that the immune cell content differs markedly among the different types of inflammatory periapical lesions. The purpose of this study was to correlate the histologic and immunologic findings with the presence of bacteria in human periapical lesions. Methods: We obtained tissue from periapical lesions obtained by apical surgery. Periapical tissues were formalin fixed and embedded in paraffin. Sections were cut and stained with hematoxylin and eosin, a variety of antibodies to identify T lymphocyte subpopulations, macrophages and NK cells and Gram’s stain to identify bacteria. Results: Histologically, the tissue obtained from the lesions in our clinic was either granulation tissue with a dense lymphocytic and plasmacytic infiltrate or fibrous connective tissue with few inflammatory cells. Tissues with large numbers of bacteria had macrophages, natural killer cells and plasma cells as the predominant immune cells. In contrast, tissues with few or no detectable bacteria predominantly contained T lymphocytes and occasional macrophages. Conclusions: The presence of bacteria in periapical lesions correlates with the immune cell content and histologic features of periapical lesions.