Secretory leukocyte protease inhibitor: inhibition of human immunodeficiency virus-1 infection of monocytic THP-1 cells by a newly cloned protein

Gingival tissue as a reservoir for human immunodeficiency virus type 1: Preliminary results of a cross-sectional observational study

BACKGROUND

Despite combined antiretroviral therapy (cART), total cure of immunodeficiency virus type 1 (HIV-1) infection remains elusive. Chronic periodontitis (CP) is strongly associated with HIV-1 infection. This condition is characterized by an intense inflammatory infiltrate mainly constituted of immune cells which in turn may be a valuable source of HIV-1 reactivation. This study aimed to determine if gingival tissue could act as a reservoir for HIV-1.

METHODS

Twelve patients with HIV-1 and CP and 12 controls (no HIV-1-infection and no CP) were evaluated in a cross-sectional study. RNA viral load and interleukin (IL) levels were determined in blood plasma and saliva. Histological sections of gingival tissue were stained with fluorescent antibodies against p24 antigen and different cellular biomarkers.

RESULTS

In six of the 12 patients, HIV RNA load was detected, despite cART; in three of them, expression of viral RNA was also detected in saliva. The levels of IL-2, IL-6, and IL-12 were higher in blood and saliva of patients with HIVand CP than controls. HIV-1 p24 antigen was detected by immunostaining in gingival biopsies of 10 of the 12 patients but in no controls. Immune markers for T cells and antigen-presenting cells were also identified in most patients and some controls.

CONCLUSION

These preliminary data showing the detection of HIV-1 p24 antigen in the gingival biopsies of a significant part of patients with HIV-1 and CP under cART together with the presence of immune cells, plead for the existence of a HIV-1 reservoir in the gingival tissue of this population.

Oral Mucosal Immunity and HIV/SIV Infection

Human Immunodeficiency Virus (HIV) transmission through genital and rectal mucosa has led to intensive study of mucosal immune responses to HIV and to the development of a vaccine administered locally. However, HIV transmission through the oral mucosa is a rare event. The oral mucosa represents a physical barrier and contains immunological elements to prevent the invasion of pathogenic organisms. This particular defense differs between micro-compartments represented by the salivary glands, oral mucosa, and palatine tonsils. Secretory immunity of the salivary glands, unique features of cellular structure in the oral mucosa and palatine tonsils, the high rate of oral blood flow, and innate factors in saliva may all contribute to the resistance to HIV/Simian Immunodeficiency Virus (SIV) oral mucosal infection. In the early stage of HIV infection, humoral and cellular immunity and innate immune functions in oral mucosa are maintained. However, these particular immune responses may all be impaired as a result of chronic HIV infection. A better understanding of oral mucosal immune mechanisms should lead to improved prevention of viral and bacterial infections, particularly in immunocompromised persons with Acquired Immune Deficiency Syndrome (AIDS), and to the development of a novel strategy for a mucosal AIDS vaccine, as well as vaccines to combat other oral diseases, such as dental caries and periodontal diseases.

Innate Humoral Defense Factors

Although innate immunity came into the research spotlight in the late 1990s when its instructive role in the adaptive immune response was recognized, innate humoral defense factors have a much older history. The exocrine secretions of the body contain a plethora of distinct soluble factors (lysozyme, lactoferrin, peroxidases, proline-rich proteins, histatins, etc.) that protect the body from mucosal microbial pathogens. More recent studies have established that the humoral arm of innate immunity contains a heterogeneous group of pattern-recognition molecules (e.g., pentraxins, collectins, and ficolins), which perform diverse host-defense functions, such as agglutination and neutralization, opsonization, control of inflammation, and complement activation and regulation. These pattern-recognition molecules, which act as functional predecessors of antibodies (“ante-antibodies”), and the classic soluble innate defense factors form an integrated system with complementary specificity, action, and tissue distribution, and they are the subject of this chapter.

Secreted mucosal antimicrobials in the female reproductive tract that are important to consider for HIV prevention

The mucosal microenvironment of the female reproductive tract (FRT) is rich in secreted endogenous antimicrobials that provide the first line of defense against pathogens. This review focuses on the spectrum of secreted antimicrobials found in the FRT that have anti-HIV functions and are regulated by the natural hormonal changes in women's life cycle. Understanding the complex nature of FRT, mucosal microenvironment will enable us to better design therapeutic interventions for women against sexually transmitted pathogens.

Secretory leukocyte protease inhibitor modulates urethane-induced lung carcinogenesis

Secretory leukocyte protease inhibitor (SLPI), 11.7 kDa serine protease inhibitor, is produced primarily in the respiratory tract, but it is often elevated in lung, head/neck and ovarian cancers. SLPI expression in relation to cancer progression, metastasis and invasion has been studied extensively in non-small cell lung cancer. However, the role of SLPI during the early stages of carcinogenesis remains unknown. We hypothesized that SLPI is required from the initiation and promotion to the progression of lung carcinogenesis. A skin allograft model using SLPI-knockout (SLPI-KO) mice and short hairpin RNA-treated cells was used to demonstrate that SLPI expression in tumor cells is crucial for tumor formation. Moreover, lung tumorigenesis induced by urethane, a chemical lung carcinogen, was significantly suppressed in SLPI-KO mice in association with decreased nuclear factor-kappaB (NF-κB) activity. SLPI deficiency also resulted in decreased cell numbers and decreased production of inflammatory cytokines in bronchoalveolar lavage fluids. The suppression of NF-κB activation in SLPI-KO mice was associated with lower expression of NF-κB-related survival genes and DNA repair genes. Our findings demonstrate that SLPI plays an important role from the initial stages of lung carcinogenesis to the progression of lung cancer in an NF-κB-dependent manner.

Structure basis 1/2SLPI and porcine pancreas trypsin interaction

SLPI (secretory leukocyte protease inhibitor) is a 107-residue protease inhibitor which inhibits various serine proteases, including elastase, cathepsin G, chymotrypsin and trypsin. SLPI is obtained as a multiple inhibitor in lung defense and in chronic airway infection. X-ray crystal structures have so far reported that they are full-length SLPIs with bovine α-chymotrypsin and 1/2SLPI (recombinant C-terminal domain of SLPI; Arg58-Ala107) with HNE (human neutrophil elastase). To understand the role of this multiple inhibitory mechanism, the crystal structure of 1/2SLPI with porcine pancreas trypsin was solved and the binding modes of two other complexes compared. The Leu residue surprisingly interacts with the S1 site of trypsin, as with chymotrypsin and elastase. The inhibitory mechanism of 1/2SLPI using the wide primary binding site contacts (from P2' to P5) with various serine proteases is discussed. These inhibitory mechanisms have been acquired in the evolution of the protection system for acute inflammatory diseases.

Genital tract viral load in HIV Type 1-positive women correlates with specific cytokine levels in cervical-vaginal secretions but is not a determinant of infectious virus or anti-HIV activity

As the AIDS epidemic continues with women being disproportionately affected, it is crucial to understand factors that predict the risk of heterosexual HIV-1 transmission. We investigated whether genital tract viral load (GTVL) in cervical-vaginal lavages (CVL) from HIV-1-positive women with moderately low CD4 T cell counts correlates with cytokine levels, antimicrobial concentrations, and intrinsic anti-HIV activity. CVL were collected from 19 HIV-1-positive women with moderately low CD4 T cell counts [mean 381 cells/mm(3) (227-536 cells/mm(3))]. None of the women was on antiretroviral therapy. The women were categorized into those with detectable GTVL or those with undetectable GTVL (detectable GTVL RNA levels > 400 copies/ml). Women were also categorized according to bacterial vaginosis (BV) status irrespective of GTVL. The TZM-bl assay was used to determine the presence of infectious virus and anti-HIV activity. Significantly higher levels of RANTES, Eotaxin, Fractalkine, IL-1α, IL-6, MCP-1, MIP1β, MIP1α, TNF-α, and GM-CSF were observed in women with detectable GTVL compared to women with undetectable GTVL. No significant differences were observed in the following cytokines and chemokines: G-CSF, IL-1RA, IL-8, and IP-10. GTVL did not correlate either with antimicrobials known to have anti-HIV activity or with the presence of infectious virus. BV status did not have a significant effect on anti-HIV activity. These findings further our understanding of the role of GTVL in determining the cytokine and chemokine milieu in the female reproductive tract.

New approaches to making the microenvironment of the female reproductive tract hostile to HIV

The studies presented in this review explore three distinct areas with potential for inhibiting HIV infection in women. Based on emerging information from the physiology, endocrinology and immunology of the female reproductive tract (FRT), we propose unique 'works in progress' for protecting women from HIV. Various aspects of FRT immunity are suppressed by estradiol during the menstrual cycle, making women more susceptible to HIV infection. By engineering commensal Lactobacillus to secrete the anti-HIV molecule Elafin as estradiol levels increase, women could be protected from HIV infection. Selective estrogen response modifiers enhance barrier integrity and enhance secretion of protective anti-HIV molecules. Finally, understanding the interactions and regulation of FRT endogenous antimicrobials, proteases, antiproteases, etc., all of which are under hormonal control, will open new avenues to therapeutic manipulation of the FRT mucosal microenvironment. By seeking new alternatives to preventing HIV infection in women, we may finally disrupt the HIV pandemic.

Expression and characterization of recombinant human secretory leukocyte protease inhibitor (SLPI) protein from Pichia pastoris

The human secretory leukocyte protease inhibitor (SLPI) has been shown to possess anti-protease, anti-inflammatory and antimicrobial properties. Its presence in saliva is believed to be a major deterrent to oral transmission of human immunodeficiency virus-1. The 11.7kDa peptide is a secreted, nonglycosylated protein rich in disulfide bonds. Currently, recombinant SLPI is only available as an expensive bacterial expression product. We have investigated the utility of the methylotrophic yeast Pichia pastoris to produce and secrete SLPI with C-terminal c-myc and polyhistidine tags. The post-transformational vector amplification protocol was used to isolate strains with increased copy number, and culturing parameters were varied to optimize SLPI expression. Modification of the purification procedure allowed the secreted, recombinant protein to be isolated from the cell-free fermentation medium with cobalt affinity chromatography. This yeast-derived SLPI was shown to have an anti-protease activity comparable to the commercially available bacterial product. Thus, P. pastoris provides an efficient, cost-effective system for producing SLPI for structure function analysis studies as well as a wide array of potential therapeutic applications.

The phospholipid scramblases 1 and 4 are cellular receptors for the secretory leukocyte protease inhibitor and interact with CD4 at the plasma membrane

Secretory leukocyte protease inhibitor (SLPI) is secreted by epithelial cells in all the mucosal fluids such as saliva, cervical mucus, as well in the seminal liquid. At the physiological concentrations found in saliva, SLPI has a specific antiviral activity against HIV-1 that is related to the perturbation of the virus entry process at a stage posterior to the interaction of the viral surface glycoprotein with the CD4 receptor. Here, we confirm that recombinant SLPI is able to inhibit HIV-1 infection of primary T lymphocytes, and show that SLPI can also inhibit the transfer of HIV-1 virions from primary monocyte-derived dendritic cells to autologous T lymphocytes. At the molecular level, we show that SLPI is a ligand for the phospholipid scramblase 1 (PLSCR1) and PLSCR4, membrane proteins that are involved in the regulation of the movements of phospholipids between the inner and outer leaflets of the plasma membrane. Interestingly, we reveal that PLSCR1 and PLSCR4 also interact directly with the CD4 receptor at the cell surface of T lymphocytes. We find that the same region of the cytoplasmic domain of PLSCR1 is involved in the binding to CD4 and SLPI. Since SLPI was able to disrupt the association between PLSCR1 and CD4, our data suggest that SLPI inhibits HIV-1 infection by modulating the interaction of the CD4 receptor with PLSCRs. These interactions may constitute new targets for antiviral intervention.

Cervicovaginal levels of lactoferrin, secretory leukocyte protease inhibitor, and RANTES and the effects of coexisting vaginoses in human immunodeficiency virus (HIV)-seronegative women with a high risk of heterosexual acquisition of HIV infection

Innate immune factors in mucosal secretions may influence human immunodeficiency virus type 1 (HIV-1) transmission. This study examined the levels of three such factors, genital tract lactoferrin [Lf], secretory leukocyte protease inhibitor [SLPI], and RANTES, in women at risk for acquiring HIV infection, as well as cofactors that may be associated with their presence. Women at high risk for HIV infection meeting established criteria (n = 62) and low-risk controls (n = 33) underwent cervicovaginal lavage (CVL), and the CVL fluid samples were assayed for Lf and SLPI. Subsets of 26 and 10 samples, respectively, were assayed for RANTES. Coexisting sexually transmitted infections and vaginoses were also assessed, and detailed behavioral information was collected. Lf levels were higher in high-risk (mean, 204 ng/ml) versus low-risk (mean, 160 ng/ml, P = 0.007) women, but SLPI levels did not differ, and RANTES levels were higher in only the highest-risk subset. Lf was positively associated only with the presence of leukocytes in the CVL fluid (P < 0.0001). SLPI levels were lower in women with bacterial vaginosis [BV] than in those without BV (P = 0.04). Treatment of BV reduced RANTES levels (P = 0.05). The influence, if any, of these three cofactors on HIV transmission in women cannot be determined from this study. The higher Lf concentrations observed in high-risk women were strongly associated with the presence of leukocytes, suggesting a leukocyte source and consistent with greater genital tract inflammation in the high-risk group. Reduced SLPI levels during BV infection are consistent with an increased risk of HIV infection, which has been associated with BV. However, the increased RANTES levels in a higher-risk subset of high-risk women were reduced after BV treatment.

Proinflammatory and type 1 cytokine expression in cervical mucosa during HIV-1 and human papillomavirus infection

Suppression of immune activation and increased inflammation are prevalent during viral infection. To investigate the role of inflammation in HIV transmission, we studied the infectious and inflammatory milieu in cervical mucosa from HIV-1- and human papillomavirus (HPV)-coinfected and HPV-monoinfected women. The numbers of cytokine-, chemokine-, and p24-expressing cells were determined using in situ imaging analysis and intracellular staining of p24 antigen. Significantly higher expression of the proinflammatory cytokines, interleukin (IL)-1alpha/beta, was seen in cervical tissue from HIV/HPV-coinfected as compared with HPV-monoinfected tissues, whereas IL-2- and interferon (IFN)-gamma-expressing cells were higher in HPV-monoinfected tissues. IL-10 was low in both groups, whereas IL-4 was significantly higher in HPV-monoinfected and HIV/HPV-coinfected tissues than in HIV/HPV-negative controls. RANTES and macrophage inflammatory protein (MIP)-1beta but not MIP-1alpha were significantly higher in the genital tract of HIV/HPV-coinfected as compared with HPV-monoinfected individuals and controls. HIV/HPV-coinfected tissues had a higher level of human leukocyte antigen D-related (HLA-DR)-expressing dendritic cells (DCs). There was a positive correlation between the number of CD4(+) and CD8(+) T cells as well as CD1a, IL-1alpha, and RANTES expression and p24 antigen-expressing cells in the HIV/HPV-coinfected tissues. These findings suggest the persistence of immune activation and inflammation in the genital tract of women with HPV monoinfection and in HIV-infected women coinfected with HPV.

Mucosal innate immune factors in secretions from high-risk individuals immunized with a bivalent gp120 vaccine

This study examined the effect of an HIV vaccine on mucosal innate factor expression. Serum, gingival fluid, and genital mucosal secretions were collected from high-risk women and men enrolled in an HIV-1 efficacy vaccine trial and from low-risk women and men. Samples were tested by standard ELISA for lactoferrin, myeloid-related protein-8/14, and secretory leukocyte protease inhibitor. No consistent significant changes in innate factor levels were found in serum or secretions from vaccinees compared to placebo recipients or from high-risk compared to low-risk individuals. Because of the importance of innate immunity in host defense, evaluation of the mucosal innate immune system should be included in future HIV prevention trials.

Comparison of human immunodeficiency virus type 1-specific inhibitory activities in saliva and other human mucosal fluids

Several human mucosal fluids are known to possess an innate ability to inhibit human immunodeficiency virus type 1 (HIV-1) infection and replication in vitro. This study compared the HIV-1 inhibitory activities of several mucosal fluids, whole, submandibular/sublingual (sm/sl), and parotid saliva, breast milk, colostrum, seminal plasma, and cervicovaginal secretions, from HIV-1-seronegative donors by using a 3-day microtiter infection assay. A wide range of HIV-1 inhibitory activity was exhibited in all mucosal fluids tested, with some donors exhibiting high levels of activity while others showed significantly lower levels. Colostrum, whole milk, and whole saliva possessed the highest levels of anti-HIV-1 activity, seminal fluid, cervicovaginal secretions, and sm/sl exhibited moderate levels, and parotid saliva consistently demonstrated the lowest levels of HIV-1 inhibition. Fast protein liquid chromatography gel filtration studies revealed the presence of at least three distinct peaks of inhibitory activity against HIV-1 in saliva and breast milk. Incubation of unfractionated and fractionated whole saliva with antibodies raised against human lactoferrin (hLf), secretory leukocyte protease inhibitor (SLPI), and, to a lesser extent, MG2 (high-molecular-weight mucinous glycoprotein) reduced the HIV-1 inhibitory activity significantly. The results suggest that hLf and SLPI are two key components responsible for HIV-1 inhibitory activity in different mucosal secretions. The variation in HIV inhibitory activity between the fluids and between individuals suggests that there may be major differences in susceptibility to HIV infection depending both on the individual and on the mucosal fluid involved.

Altered expression of CLC, DSG3, EMP3, S100A2, and SLPI in corneal epithelium from keratoconus patients

PURPOSE

This investigation was designed to determine whether the five genes, CLC, DSG3, EMP3, S100A2 and SLPI, are differentially expressed in keratoconus, as indicated from another study.

METHODS

Gene expression was monitored using quantitative real-time PCR on 14 keratoconus samples and 16 controls, and normalized to GAPDH and B2M. The DSG3, S100A2, and SLPI proteins were quantified by Western blotting, and the cellular localization was determined by immunohistochemistry. One of the genes, CLC, was reduced in gene expression and its four exons were sequenced.

RESULTS

The five genes were all differentially expressed in keratoconus (P < 0.04) and so were at least three of the encoded proteins (P = 0.009). DSG3 was expressed in association with the cell membrane of the basal and suprabasal epithelial cells, and S100A2 was expressed in the nucleus and cytoplasm, often as intracellular granules. Two SNPs (rs374185 and rs384138) were observed in the CLC gene, each with an allele frequency of 68%. No other mutations were detected.

CONCLUSIONS

The five genes, and three of the encoded proteins, were shown differentially expressed between a group of keratoconus patients and a reference group using different techniques. These alterations, in combination with earlier findings, strongly demonstrate the genes to be involved in the corneal disease. We suggest the unambiguously expressed DSG3 protein to be used as a marker for keratoconus.

Human immunodeficiency virus type 1 stimulates the expression and production of secretory leukocyte protease inhibitor (SLPI) in oral epithelial cells: a role for SLPI in innate mucosal immunity

The innate immune response is a key barrier against pathogenic microorganisms such as human immunodeficiency virus type 1 (HIV-1). Because HIV-1 is rarely transmitted orally, we hypothesized that oral epithelial cells participate in the innate immune defense against this virus. We further hypothesized that secretory leukocyte protease inhibitor (SLPI), a 12-kDa mucosal antiviral protein, is a component of the host immune response to this virus. Here we demonstrated constitutive expression and production of SLPI in immortalized human oral keratinocytes. Brief exposure of cells to HIV-1 BaL and HXB2 significantly increased SLPI mRNA and protein production compared to that in mock-exposed cells (P < 0.01), as evaluated by real-time quantitative reverse transcription-PCR and enzyme-linked immunosorbent assay. HIV-1-mediated stimulation of SLPI occurred at the transcriptional level, was dose and time dependent, was elicited by heat-inactivated and infectious viruses, and did not depend on cellular infection. Experiments with purified retroviral proteins showed that the stimulatory effect was induced specifically by external envelope glycoproteins from HIV-1 and simian immunodeficiency virus. SLPI responsiveness to HIV-1 was also observed in an unrelated oral epithelial cell line and in normal (nonimmortalized) human oral epithelial cells isolated from healthy uninfected gingival tissues. In this first report of SLPI regulation by HIV-1, we show that the expression and production of the antimicrobial and anti-inflammatory protein can be stimulated in oral epithelial cells by the virus through interactions with gp120 in the absence of direct infection. These findings indicate that SLPI is a component of the oral mucosal response to HIV-1.

Salivary secretory leukocyte protease inhibitor and oral candidiasis in human immunodeficiency virus type 1-infected persons

Oropharyngeal candidiasis, typically caused by Candida albicans, is the most common oral disease associated with human immunodeficiency virus type 1 (HIV-1) infection. Secretory leukocyte protease inhibitor (SLPI), a 12-kDa antiprotease, suppresses the growth of C. albicans in vitro. To determine whether the mucosal protein plays a role in protecting oral tissues against fungal infection, we conducted a cross-sectional study investigating the oral and systemic health and salivary SLPI levels in 91 dentate HIV-1-infected adults receiving medical care in the southeastern United States. Participants with a self-reported history of clinical oropharyngeal candidiasis during the previous 2 years constituted the test group (n = 52), while the comparison group (n = 39) had no oropharyngeal candidiasis during that period. Data collected from medical records, oral examination, and SLPI enzyme-linked immunosorbent assay quantitation of whole saliva were analyzed by t test, analysis of variance, linear regression, and unconditional logistic regression. The test group had a significantly higher mean salivary SLPI level than the comparison group (1.9 microg/ml versus 1.1 microg/ml, P < 0.05). Linear regression modeling identified CD4 cell count and history of oropharyngeal candidiasis as key predictors of salivary SLPI and revealed a significant interaction (P < 0.05) between immunosuppression (CD4 cell count below 200 cells/ microl) and positive history of oropharyngeal candidiasis in predicting salivary SLPI level. By logistic regression modeling, a salivary SLPI level exceeding 2.1 microg/ml, low CD4 count, antiretroviral monotherapy, and smoking were key predictors of oropharyngeal candidiasis. These data support a key role for SLPI in the oral mucosal defense against C. albicans. The antimicrobial mucosal protein may serve as an indicator of previous oropharyngeal candidiasis infection among immunosuppressed persons.