Interaction of gram-negative periodontal pathogens with retinoic acid-induced and dimethyl sulfoxide-induced HL-60 cells

Opsonophagocytic effect of antibody against recombinant conserved 40-kDa outer membrane protein of Porphyromonas gingivalis

BACKGROUND

Porphyromonas gingivalis is associated with the initiation and progression of adult periodontitis. The outer membrane proteins of the bacteria are potentially important targets for interaction with host defense systems. A 40-kDa outer membrane protein (40-kDa OMP) is conserved among many strains of P. gingivalis. We have cloned the gene for 40-kDa OMP from P. gingivalis 381 and produced a recombinant protein. For the development of recombinant 40-kDa OMP as a component of a vaccine for passive immunization, the elucidation of the roles of the anti-recombinant 40-kDa OMP antibody in the host defense against P. gingivalis is essential. The objective of this study was to determine the opsonic capacity of the antibody for phagocytosis by neutrophils which play a key role in the immune response to microbial infections.

METHODS

To test the opsonic activity of a rabbit polyclonal antibody against r40-kDa OMP (r40-kDa OMP Ab) on human neutrophils to phagocytize P. gingivalis, we constructed a reproducible in vitro model of P. gingivalis-neutrophil interaction using the human promyelocytic cell line HL-60.

RESULTS

We demonstrated that r40-kDa OMP Ab in the presence of human complement successfully opsonized [3H]-thymidine-labeled P. gingivalis as a target for phagocytosis by HL-60 cells differentiated with dimethyl sulfoxide. The phagocytized bacteria were then intracellularly killed and lysed, and the radioactive degradation debris egested into the culture medium.

CONCLUSIONS

We conclude that antibody against r40-kDa OMP has opsonic activity on human neutrophil function for phagocytosis of P. gingivalis. Subgingival bacteria are coated in vivo with immunoglobulin and complement. When the antibody is specific for crevicular bacteria, immunological interactions can be expected in the crevice. Our observations suggest that the anti-recombinant 40-kDa OMP antibody in concert with the crevicular complement may prevent P. gingivalis colonization r40-kDa OMP may contribute to the development of a local immunotherapy when applied to the crevice of a patient with P. gingivalis-related periodontitis which relates to susceptibility for certain systemic diseases such as diabetes mellitus, cardiovascular disease, and preterm labor.

Campylobacter rectus in human periodontitis

Campylobacter rectus (formerly Wolinella recta) in periodontitis lesions was studied relative to age and sex distribution, relationship to disease-active periodontitis, response to periodontal debridement and in vitro antimicrobial susceptibility. Subgingival C. rectus was collected with paper points, transported in VMGA III and plated onto nonselective enriched brucella blood agar and Hammond's selective medium for C. rectus, both incubated anaerobically. C. rectus was recovered from 80% of 1654 periodontitis patients. Although the organism showed similar age and sex occurrence, its proportional recovery in culture-positive adults was inversely related to increasing age (r = 0.999, P < 0.001). The organism was positively associated (summary odds ratio = 2.95) with disease activity in a 24-month longitudinal study of 93 adult periodontitis patients on maintenance therapy. C. rectus decreased from 8.2% to 0.7% following local periodontal debridement of 20 culture-positive adult periodontitis patients. The organism exhibited high in vitro susceptibility to therapeutic levels of tetracycline hydrochloride, metronidazole, penicillin G and ciprofloxacin. These findings further delineate the epidemiology and potential pathogenic role of C. rectus in human periodontitis.

Virulence of Wolinella recta in a murine abscess model

The virulence of Wolinella recta isolates was studied in an experimental animal model by using monoinfection of BALB/c mice. Infection with clinical isolates of W. recta 576 and W. recta 234 induced dry, flat, depressed gangrenous necrotic skin lesions, whereas W. recta ATCC 33238 failed to induce a similar lesion. Histological examination of the skin lesion 72 h postinfection revealed coagulation necrosis of the epidermis, subcutis and cutaneous truncus muscle, with marked exudation of serum proteins and neutrophils. Virulence-modulating agents such as dexamethasone, galactosamine, hydrazine sulfate, and dextran microcarrier beads were used in conjunction with W. recta infection. Dexamethasone, hydrazine sulfate, and dextran beads enhanced the infectivity and pathogenicity of W. recta for lesion formation and tissue destruction compared with what was found in untreated control mice. Galactosamine sensitization enhanced the virulence potential of W. recta to such an extent that a lethal outcome was observed. Laboratory passage of clinical isolates demonstrated a decreased virulence in high-passage strains, which correlated with the minimal virulence observed in the extensively passaged W. recta ATCC 33238. Serum immunoglobulin G (IgG) and IgM responses were detected in the serum of infected animals, and cross-reacting antibody indicated variation in the antigenic makeup of various W. recta strains. Enhanced IgG antibody responses were observed following the secondary challenge. Mice with acquired antibody response to initial infection remained susceptible to lesion formation with subsequent challenge, but the size of the lesion was significantly reduced, indicating partial protection. Serum IgG and IgM antibody levels were significantly increased by active immunization when compared with levels in mice which had recovered from infection. The immunization significantly decreased the lesion size; however, even these high levels of antibody failed to abrogate the lesion induction.

Phagocytosis of virulent Porphyromonas gingivalis by human polymorphonuclear leukocytes requires specific immunoglobulin G

No studies to date clearly define the interactions between Porphyromonas gingivalis and human peripheral blood polymorphonuclear leukocytes (PMN), nor has a protective role for antibody to P. gingivalis been defined. Using a fluorochrome phagocytosis microassay, we investigated PMN phagocytosis and killing of P. gingivalis as a function of P. gingivalis-specific antibody. Sera from a nonimmune rabbit and a healthy human subject were not opsonic for virulent P. gingivalis A7436, W83, and HG405; phagocytosis of these strains (but not 33277) required opsonization with hyperimmune antiserum (RaPg). Diluting RaPg with a constant complement source decreased proportionally the number of P. gingivalis A7436 cells phagocytosed per phagocytic PMN. Enriching for the immunoglobulin G fraction of RAPg A7436 enriched for opsonic activity toward A7436. An opsonic evaluation of 18 serum samples from adult periodontitis patients revealed that only 3 adult periodontitis sera of 17 with elevated immunoglobulin G to P. gingivalis A7436 were opsonic for A7436 and, moreover, that the serum sample with the highest enzyme-linked immunosorbent assay titer was most opsonic (patient 1). However, the opsonic activity of serum from patient 1 was qualitatively and not just quantitatively different from that of the nonopsonic human sera (but was less effective opsonin than RaPg). Strain variability was observed in resistance of P. gingivalis to phagocytosis, and opsonization was strain specific for some, but not all, strains tested. An evaluation of killing of A7436 revealed that serum killing and extracellular killing of P. gingivalis were less effective alone when compared with intracellular PMN killing alone.