Enhanced phagocytosis of Aggregatibacter actinomycetemcomitans cells by macrophages activated by a probiotic Lactobacillus strain

The activation of phagocytosis is one important approach to clearing pathogenic cells in a host. This study evaluated the ability of probiotic lactobacilli to induce phagocytic activity as well as the clearance of a periodontal pathogen, Aggregatibacter actinomycetemcomitans. First, the activation of phagocytosis was found by using lyophilized dead cells. Probiotic Lactobacillus strains significantly enhanced the phagocytic activity of macrophage cells, indicating that the probiotic lactobacilli have a remarkable ability to stimulate the macrophages. Essentially, 3 Lactobacillus strains tested did not have any critical toxic effect on the murine macrophage, and Lactobacillus johnsonii NBRC 13952 showed the least cytotoxic effect on the RAW264.7 macrophages. The expression of classically activated macrophage markers, IL-1β, and cluster of differentiation 80 increased by L. johnsonii NBRC 13952; however, there was no significant difference for IL-18. The highest phagocytic activity by macrophages was found in a condition in which the macrophage activated by L. johnsonii NBRC 13952 functions to kill the cells of A. actinomycetemcomitans. Correlating with the result, a high amount of hypodiploid DNA (SubG1) was detected from the macrophage cells stimulated by L. johnsonii NBRC 13952. Taken together, the results suggest that macrophages activated by the Lactobacillus strain can facilitate the phagocytosis of A. actinomycetemcomitans cells by linking with enhanced apoptotic activities. In conclusion, L. johnsonii NBRC 13952 has a certain role in activating the RAW264.7 macrophages, thereby counteracting the infection of A. actinomycetemcomitans.