Neisseria gonorrhoeae-induced human defensins 5 and 6 increase HIV infectivity: role in enhanced transmission.

Sexually transmitted infections (STIs) increase the likelihood of HIV transmission. Defensins are part of the innate mucosal immune response to STIs and therefore we investigated their role in HIV infection. We found that human defensins 5 and 6 (HD5 and HD6) promoted HIV infection, and this effect was primarily during viral entry. Enhancement was seen with primary viral isolates in primary CD4(+) T cells and the effect was more pronounced with R5 virus compared with X4 virus. HD5 and HD6 promoted HIV reporter viruses pseudotyped with vesicular stomatitis virus and murine leukemia virus envelopes, indicating that defensin-mediated enhancement was not dependent on CD4 and coreceptors. Enhancement of HIV by HD5 and HD6 was influenced by the structure of the peptides, as loss of the intramolecular cysteine bonds was associated with loss of the HIV-enhancing effect. Pro-HD5, the precursor and intracellular form of HD5, also exhibited HIV-enhancing effect. Using a cervicovaginal tissue culture system, we found that expression of HD5 and HD6 was induced in response to Neisseria gonorrhoeae (GC, for gonococcus) infection and that conditioned medium from GC-exposed cervicovaginal epithelial cells with elevated levels of HD5 also enhanced HIV infection. Introduction of small interfering RNAs for HD5 or HD6 abolished the HIV-enhancing effect mediated by GC. Thus, the induction of these defensins in the mucosa in the setting of GC infection could facilitate HIV infection. Furthermore, this study demonstrates the complexity of defensins as innate immune mediators in HIV transmission and warrants further investigation of the mechanism by which defensins modulate HIV infection.

The antifungal activity of RsAFP2, a plant defensin from raphanus sativus, involves the induction of reactive oxygen species in Candida albicans.

RsAFP2 (Raphanus sativus antifungal peptide 2), an antifungal plant defensin isolated from seed of R. sativus, interacts with glucosylceramides (GlcCer) in membranes of susceptible yeast and fungi and induces membrane permeabilization and fungal cell death. However, using carboxyfluorescein-containing small unilamellar vesicles containing purified GlcCer, we could not observe permeabilization as a consequence of insertion of RsAFP2 in such vesicles. Therefore, we focused on a putative RsAFP2-induced signaling cascade downstream of RsAFP2-binding to GlcCer in fungal membranes. We show that RsAFP2 induces reactive oxygen species (ROS) in Candida albicans wild type in a dose-dependent manner, but not at all in an RsAFP2-resistant DeltagcsC. albicans mutant that lacks the RsAFP2-binding site in its membranes. These findings indicate that upstream binding of RsAFP2 to GlcCer is needed for ROS production leading to yeast cell death. Moreover, the antioxidant ascorbic acid blocks RsAFP2-induced ROS generation, as well as RsAFP2 antifungal activity. These data point to the presence of an intracellular plant defensin-induced signaling cascade, which involves ROS generation and leads to fungal cell growth arrest.

Yersinia's stratagem: targeting innate and adaptive immune defense.

In contrast to Salmonella and Shigella, enteropathogenic Yersinia species are extracellular multiplying Gram-negative bacteria. This life style requires a sophisticated anti-host strategy, which is implemented by the Yersinia virulence plasmid. This plasmid encodes the type 3 secretion system (injectisome), at least six microinjected anti-host effector proteins, a trimeric coiled coil outer membrane protein (Yersinia adhesin) with cell adhesin and protective functions against complement and defensins, and the released V antigen, which has Toll-like receptor 2 agonist activity.

Assessment of the cellular response to the induced expression of defensin sense and antisense cDNA in acute promyelocytic leukemia cell lines.

Defensins are 20-30 amino acid-long, cystine- and arginine-rich peptides that constitute more than 5% of the total cellular proteins in mature granulocytes and at least 30% of proteins in primary granules. Human defensins were reported to have antimicrobial, antifungal, antiviral and tumor lysis activities. Defensin mRNA was isolated using the differential display technique from the well-characterized all-trans retinoic acid (ATRA)-responsive acute promyelocytic leukemia cell line, NB4. The differential display analysis showed an up-regulation of defensin mRNA in NB4 cells after treatment with 10(-7) M ATRA for 24 h. This expression was not seen in an NB4:R2 cell line, an ATRA-resistant subclone of NB4 cells. In order to investigate further the effects of this gene on our cellular model, we virally infected our cells with full-length defensin cDNA in the sense and antisense directions. Sense defensin induced cell growth arrest and cell death in both cell lines. While NB4 cells died within 48-73 h, NB4:R2 cells survived for 96 h before dying in culture. Phenotypic analysis showed high expression of Annexin V in sense-infected cells compared with antisense and uninfected cells in both cell lines. There was not a significant increase in CD11b expression in any of the 2 cell lines used. No cellular response was encountered in antisense-infected cells. Our data suggest that defensin is not only a reliable marker for granulocytic differentiation, but can also be considered a candidate target for molecular therapy in acute promyelocytic leukemia.