A Novel Factor Isolated fromActinobacillus actinomycetemcomitansStimulates Mouse B Cells and Human Peripheral Blood Mononuclear Cells

Abstract

A novel immunostimulating factor (ISTF) of Actinobacillus actinomycetemcomitans ATCC 29522 was isolated and characterized as inducing proliferation of mouse B cells and human peripheral blood mononuclear cells. This factor was isolated from the bacterial culture medium and purified by size exclusion chromatography, dye-ligand affinity chromatography, immunoaffinity chromatography using monoclonal antibodies, and preparative electrophoresis. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that the purified ISTF migrated as a single band corresponding to a molecular mass of 13 kDa. ISTF was a proteinaceous material distinct from lipopolysaccharide; it directly induced the proliferation of B lymphocytes but had no effect on the proliferation of T lymphocytes, even in the presence of antigen-presenting cells. A B-lymphocyte-mitogenic activity of ISTF was also shown by flow cytometric analysis of responding cell subpopulations. Immunoblot analysis revealed that ISTF was a component of the outer membranes of bacteria, could exist as a soluble form, and was released by growing and/or lysed bacteria. These results suggest that ISTF produced by A. actinomycetemcomitans may play an important role in immunopathologic changes associated with A. actinomycetemcomitans infections.Actinobacillus actinomycetemcomitans, a nonmotile, gramnegative coccobacillus, is associated with several human diseases including endocarditis, meningitis, osteomyelitis, subcutaneous abscesses, and periodontal diseases (2,8,20,24,30). Although the pathogenic mechanism of A. actinomycetemcomitans is not known, it has been proposed that the impairment of the host immune mechanism by the bacteria-producing virulence factors might contribute to the disease process. Many other studies have described several virulence factors of A. actinomycetemcomitans, which exhibited alterations in immune regulation. Immunosuppressive factor (ISF; 60 kDa) inhibited mitogen-induced T-cell proliferation and immunoglobulin (Ig) production (26,27). Suppressive factor 1 (SF1; 14 kDa) downregulated T-cell proliferation and cytokine production (13). Leukotoxin (115 kDa) inhibited the responsiveness of human peripheral blood mononuclear cells (PBMC) to mitogens and antigens by subverting monocytes (23). Lipopolysaccharide (LPS) suppressed antigen-and mitogen-induced human T-cell proliferation by inducing the release of prostaglandin E2 from activated macrophages (5). As all these factors contributed to the suppression of lymphocyte activation, it has been suggested that products of A. actinomycetemcomitans might possess a lymphocyte-activating substance like a superantigen (1,16,17,32). During studies in our laboratory focusing on an understanding of the immunomodulatory activity of the products from A. actinomycetemcomitans, we became intrigued by an indication that immunosuppressing and immunostimulating activities were present simultaneously in the bacterial preparations. A consistent pattern was observed: A. actinomycetemcomitans homogenates ...

The heat shock proteins, Hsp70 and Hsp83, of Leishmania infantum are mitogens for mouse B cells

“…Also, in the last few years, several proteins from pathogenic organisms have been described as potent mitogens of B lymphocytes. Examples of such mitogens are the 13-kDa protein fraction (called ISTF) of Actinobacillus actinomycetemcomitans (Jeong et al 2000), the exoenzyme S of Pseudomonas aeruginosa (Barclay et al 1999), and the rTc24 antigen and the proline racemase of Trypanosoma cruzi (Cordeiro da Silva et al 1998;Reina-San-Martín et al 2000b). The hypothesis that these molecules are used by the pathogens to weaken the host immune response and that these are of central importance in the pathogenesis caused by the infection has been proposed (Reina-SanMartín et al 2000a).…”

Actinobacillus actinomycetemcomitans

“…A 37-kDa secreted immunogenic glycoprotein has also been reported to stimulate murine macrophages to produce IL-1â, IL-6 and TNF-AE [78]. A. actinomycetemcomitans has also been reported to secrete mitogenic proteins [79], including a 13-kDa B-cell mitogen [80].…”

Biological Characterization of the Omp1-like Protein from Actinobacillus actinomycetemcomitans

“…The pathogenic mechanism for A. actinomycetemcomitans purportedly impairs the host immune mechanism by bacterial virulence factors that might contribute to disease processes. 3 In particular, the pathogenesis of periodontitis might be explained by immune stimulation by periodontopathic bacteria, which induce large scale T cell activation, cytokine production and polyclonal B cell activation. 4 The N-terminal amino acid sequence of outer membrane protein Omp26 (202 aa) from Nontypeable Haemophilus influenzae has a revealed homology to a Yersinia enterocolitica OmpH, as well as homologies to Skp (17 kDa), OmpH, and Hip-1 proteins in Pasteurella multocida, Yersinia pseudotuberculosis, Escherichia coli and Salmonella enterica.…”