Inhibitory function of secretory leukocyte proteinase inhibitor (SLPI) in human saliva is HIV-1 specific and varies with virus tropism

OBJECTIVE: Secretory leukocyte proteinase inhibitor (SLPI) is an endogenous mucosa associated protein that has been proposed to possess anti-human immunodeficiency virus type 1 (HIV-1) activity. The aim of this study was to investigate the biological function of SLPI in salivary mediated inhibition of HIV infection and in addition the inhibitory effect of SLPI using isolates of varied virus tropism. MATERIAL AND METHODS: The inhibitory effect of HIV-1 infection in vitro, mediated by 60 different saliva samples was analyzed with respect to levels of SLPI. Salivary samples depleted from IgA and SLPI, respectively, were further analyzed for anti-HIV activity. The antiviral effect of recombinant SLPI was investigated within an in vitro system of HIV-1 infection of target cells using a panel of viral isolates with distinct coreceptor usage. Furthermore we tested a panel of overlapping synthetic peptides, representing the amino acids in SLPI, for their capacity to inhibit HIV-1 infection of human peripheral blood mononuclear cells (PBMCs). RESULTS AND CONCLUSIONS: These experiments show that elevated levels of salivary SLPI can be associated with an increased inhibitory effect of the whole saliva sample, and that this inhibitory effect is decreased with broad coreceptor usage of the virus.     

Arginine-specific gingipains from Porphyromonas gingivalis deprive protective functions of secretory leucocyte protease inhibitor in periodontal tissue

Chronic periodontitis is correlated with Porphyromonas gingivalis infection. In this study, we found that the expression of secretory leucocyte protease inhibitor (SLPI), an endogenous inhibitor for neutrophil-derived proteases, was reduced in gingival tissues with chronic periodontitis associated with P. gingivalis infection. The addition of vesicles of P. gingivalis decreased the amount of SLPI in the media of primary human gingival keratinocytes compared to untreated cultures. We therefore investigated how arginine-specific gingipains (Rgps) affect the functions of SLPI, because Rgps are the major virulence factors in the vesicles and cleave a wide range of in-host proteins. We found that Rgps digest SLPI in vitro, suppressing the release of SLPI. Rgps proteolysis of SLPI disrupted SLPI functions, which normally suppresses neutrophil elastase and neutralizes pro-inflammatory effects of bacterial cell wall compounds in cultured human gingival fibroblasts. The protease inhibitory action of SLPI was not exerted towards Rgps. These results suggest that Rgps reduce the protective effects of SLPI on neutrophil proteases and bacterial proinflammatory compounds, by which disease in gingival tissue may be accelerated at the sites with P. gingivalis infection.     

The role of the antileukoprotease SLPI in smoking‐induced human papillomavirus‐independent head and neck squamous cell carcinomas

Recently, we showed that increased SLPI levels prevent human papillomavirus (HPV) infections and metastasis in smoking‐induced, non‐HPV‐driven head and neck squamous cell carcinoma (HNSCC). Here, we focus on the role of SLPI in non‐HPV‐driven HNSCC, investigating tumor tissue and non‐neoplastic mucosa from the same patients and from non‐HNSCC patients. Gene and protein expression of SLPI and gene expression of annexin 2 (a SLPI receptor), nicotine receptor (α7AChR) and arylhydrocarbon receptor (AhR) were analyzed in HNSCC patients (20 smokers; 16 nonsmokers). SLPI‐results were correlated with the patients' HPV status. Non‐neoplastic mucosa of HNSCC patients and normal mucosa from non‐HNSCC individuals (18 smokers; 20 nonsmokers) was analyzed for the same parameters. Tissue of the inferior turbinate (n = 10) was incubated with nicotine for analysis of the same genes. SLPI gene expression in tumor tissue was 109.26 ± 23.08 times higher in smokers versus nonsmokers. Non‐neoplastic mucosa of smokers showed also higher SLPI gene expression (10.49 ± 1.89‐fold non‐HNSCC; 18.02 ± 3.93‐fold HNSCC patients). Annexin 2 gene expression was also increased in smokers. SLPI data were corroborated by immunohistochemistry. A nicotine dependent correlation between SLPI and annexin 2 gene expression (r² = 0.15, p < 0.001) was shown ex vivo. Nicotine and smoking increased α7AChR and AhR gene expression. Five patients, showing no/low SLPI expression, were HPV16‐positive. A significant correlation between smoking and SLPI expression in tumors and to our knowledge for the first time in mucosa of HNSCC and non‐HNSCC patients was established. Together with the finding that all patients with HPV infection showed no/low SLPI expression, these data support our intriguing hypothesis that smoking induced upregulated SLPI prevents HPV infections.     

The effect of immediate‐hypersensitivity reactions on the level of SLPI, granulocyte elastase, α1‐antitrypsin, and albumin in nasal secretions, by the method of unilateral antigen challenge

BACKGROUND: The aim of this paper was to investigate the role of SLPI in patients with allergic rhinitis. From this point of view, we also examined leukocyte elastase, alpha1-antitrypsin, and albumin. SLPI is an inhibitor of serine proteases such as leukocyte elastase, cathepsin G, and mast-cell chymase. Since chymase is considered to participate in mast-cell degranulation and histamine release, SLPI might act as a regulator of allergic reactions. Recent interest has been focused on leukocytes and allergy. Since SLPI is a strong inhibitor of leukocyte elastase, we also focused on the function of elastase in allergic rhinitis. METHODS: We used the method of nasal lavage after unilateral nasal antigen challenge in atopic and healthy subjects. The ELISA quantified SLPI and elastase. Albumin and alpha1-antitrypsin were quantified by electroimmunoassay. Gel filtration was used to separate native SLPI from its complex with elastase. RESULTS: There was a higher level of SLPI in lavage fluid from healthy subjects than from atopic patients. SLPI was increased on the contralateral side in atopic subjects after allergen challenge. The absence of increase in SLPI on the challenged side may be attributed to the increase in elastase and its binding to SLPI, which might have an effect on the immunoreactivity and interfere with the ELISA. It may then be assumed that there is an augmentation of SLPI on the challenged side as well. No increase was seen in healthy subjects. There was a higher concentration of elastase, alpha1-antitrypsin, and albumin before antigen challenge in atopic patients outside the pollen season than in healthy subjects. As expected, an increase was also seen in the challenged side exclusively in atopic subjects. CONCLUSIONS: The lower concentration of SLPI in nasal lavage fluid among the atopic patients than the healthy subjects indicates damaged mucosa. Neural reflexes are involved in SLPI release since there was an increase even in the contralateral nostril. A higher level of elastase and albumin before allergen challenge suggests chronic inflammation in nasal mucosa outside the pollen season. Leukocyte recruitment takes place in response to IgE-mediated reactions, which are reflected in an increase in elastase in response to allergen challenge.