Tannerella forsythia is a poorly studied pathogen despite being one of the main causes of periodontitis, which is an inflammatory disease of the supporting structures of the teeth. We found that despite being recognized by all complement pathways, T. forsythia is resistant to killing by human complement, which is present at up to 70% of serum concentration in gingival crevicular fluid. Incubation of human serum with karilysin, a metalloproteinase of T. forsythia, resulted in a decrease in bactericidal activity of the serum. T. forsythia strains expressing karilysin at higher levels were more resistant than low-expressing strains. Furthermore, the low-expressing strain was significantly more opsonized with activated complement factor 3 and membrane attack complex from serum compared with the other strains. The high-expressing strain was more resistant to killing in human blood. The protective effect of karilysin against serum bactericidal activity was attributable to its ability to inhibit complement at several stages. The classical and lectin complement pathways were inhibited because of the efficient degradation of mannose-binding lectin, ficolin-2, ficolin-3, and C4 by karilysin, whereas inhibition of the terminal pathway was caused by degradation of C5. Interestingly, karilysin was able to release biologically active C5a peptide in human plasma and induce migration of neutrophils. Importantly, we detected the karilysin gene in >90% of gingival crevicular fluid samples containing T. forsythia obtained from patients with periodontitis. Taken together, the newly characterized karilysin appears to be an important virulence factor of T. forsythia and might have several important implications for immune evasion.

Proteases ofTannerella forsythia, a pathogen associated with periodontal disease, are implicated as virulence factors. Here, we characterized a matrix metalloprotease (MMP)-like enzyme ofT. forsythiareferred to as karilysin. Full-length (without a signal peptide) recombinant karilysin (49.9 kDa) processed itself into the mature 18-kDa enzyme through sequential autoproteolytic cleavage at both N- and C-terminal profragments. The first cleavage at the Asn14-Tyr15 peptide bond generated the fully active enzyme (47.9 kDa) and subsequent truncations at the C-terminus did not affect proteolytic activity. Mutation of Tyr15 to Ala generated a prokarilysin variant that processed itself into the final 18-kDa form with greatly reduced kinetics. Inactive prokarilysin with the mutated catalytic Glu residue (E136A) was processed by active karilysin at the same sites as the active enzymes. Karilysin proteolytic activity and autoprocessing were inhibited by 1,10-phenanthroline and EDTA. Calcium ions were found to be important for both the activity and thermal stability of karilysin. Using CLiPS technology, the specificity of karilysin was found to be similar to that of MMPs with preference for Leu/Tyr/Met at P1′ and Pro/Ala at P3. This specificity and the ability to degrade elastin, fibrinogen and fibronectin may contribute to the pathogenicity of periodontitis.

The emergence of the novel coronavirus and then pandemic outbreak was coined 2019- nCoV or COVID-19 (or SARS-CoV-2 disease 2019). This disease has a mortality rate of about 3·7 percent, and successful therapy is desperately needed to combat it. The exact cellular mechanisms of COVID-19 need to be illustrated in detail. This study aimed to evaluate serum cytokines in COVID-19 patients. In this study, serum was collected from volunteer individuals, moderate COVID-19 patients, severe cases of COVID-19 patients, and patients who recovered from COVID-19 (n = 122). The serum concentrations of interleukins such as IL-1, IL-4, IL-6, IL-8, IL-10, and tumor necrosis factor-alpha (TNF-α), were measured by enzyme-linked immunosorbent assays (ELISA). The concentrations of IL-1 and TNF-α were did not differ significantly among groups. However, the concentration of IL-6 was significantly higher in moderate COVID-19 and severe cases of COVID-19 groups compared to control and recovered groups indicating it to be an independent predictor in the coronavirus disease. The levels of IFN-γ and IL-4 were significantly lower in the recovery group than the severe case of the COVID-19 group. In contrast, the level of IL-10 in recovered COVID-19 patients was significantly higher in compare to severe cases, COVID-19 patients. Varying levels of cytokines were detected in COVID-19 group than control group suggesting distinct immunoregulatory mechanisms involved in COVID-19 pathogenesis. However, additional investigations are needed to be to be performed to understand the exact cellular mechanism of this disease.

Proteases of Staphylococcus aureus have long been considered to function as important virulence factors, although direct evidence of the role of part