Detection of cross-reactive immunoglobulin A against the severe acute respiratory syndrome-coronavirus-2 spike 1 subunit in saliva.

Abundant secretory immunoglobulin A (SIgA) in the mucus, breast milk, and saliva provides immunity against infection of mucosal surfaces. Pre-pandemic breast milk samples containing SIgA have been reported to cross-react with SARS-CoV-2; however, it remains unknown whether SIgA showing the cross-reaction with SARS-CoV-2 exists in saliva. We aimed to clarify whether SIgA in saliva cross-reacts with SARS-CoV-2 spike 1 subunit in individuals who have not been infected with this virus. The study involved 137 (men, n = 101; women, n = 36; mean age, 38.7; age range, 24-65 years) dentists and doctors from Kanagawa Dental University Hospital. Saliva and blood samples were analyzed by polymerase chain reaction (PCR) and immunochromatography for IgG and IgM, respectively. We then identified patients with saliva samples that were confirmed to be PCR-negative and IgM-negative for SARS-CoV-2. The cross-reactivity of IgA-positive saliva samples with SARS-CoV-2 was determined by enzyme-linked immunosorbent assay using a biotin-labeled spike recombinant protein (S1-mFc) covering the receptor-binding domain of SARS-CoV-2. The proportion of SARS-CoV-2 cross-reactive IgA-positive individuals was 46.7%, which correlated negatively with age (r = -0.218, p = 0.01). The proportion of IgA-positive individuals aged ≥50 years was significantly lower than that of patients aged ≤49 years (p = 0.008). SIgA was purified from the saliva of patients, which could partially suppress the binding of SARS-CoV-2 spike protein to the angiotensin converting enzyme-2 receptor. This study demonstrates the presence of SARS-CoV-2 cross-reactive SIgA in the saliva of individuals who had never been infected with the virus, suggesting that SIgA may help prevent SARS-CoV-2 infection.

Multimolecular salivary mucin complex is altered in saliva of cigarette smokers: detection of disulfide bridges by Raman spectroscopy.

Saliva contains mucins, which protect epithelial cells. We showed a smaller amount of salivary mucin, both MG1 and MG2, in the premenopausal female smokers than in their nonsmoking counterparts. Smokers' MG1, which contains almost 2% cysteine/half cystine in its amino acid residues, turned out to be chemically altered in the nonsmoker's saliva. The smaller acidic glycoprotein bands were detectable only in smoker's saliva in the range of 20-25 kDa and at 45 kDa, suggesting that degradation, at least in part, caused the reduction of MG1 mucin. This is in agreement with the previous finding that free radicals in cigarette smoke modify mucins in both sugar and protein moieties. Moreover, proteins such as amylase and albumin are bound to other proteins through disulfide bonds and are identifiable only after reduction with DTT. Confocal laser Raman microspectroscopy identified a disulfide stretch band of significantly stronger intensity per protein in the stimulated saliva of smokers alone. We conclude that the saliva of smokers, especially stimulated saliva, contains significantly more oxidized form of proteins with increased disulfide bridges, that reduces protection for oral epithelium. Raman microspectroscopy can be used for an easy detection of the damaged salivary proteins.

Essential role of the adhesion receptor LFA-1 for T cell-dependent fulminant hepatitis.

Viral hepatitis affects more than 2 billion people worldwide. In particular, no effective treatment exists to abrogate death and liver damage in fulminant hepatitis. Activation of T cells is an initial and critical event in the pathogenesis of liver damage in autoimmune and viral hepatitis. The precise molecular mechanisms that induce T cell-mediated hepatocyte injury remain largely unclear. In mice, T cell-dependent hepatitis and acute liver damage can be modeled using ConA. In this study, we examined the role of the adhesion receptor LFA-1 in ConA-induced acute hepatic damage using LFA-1(-/-) (CD11a) mice. Massive liver cell apoptosis and metabolic liver damage were observed in LFA-1(+/+) mice following ConA injection. By contrast, LFA-1(-/-) mice were completely resistant to ConA-induced hepatitis and none of the LFA-1(-/-) mice showed any hepatic damage. Whereas activated hepatic T cells remained in the liver in LFA-1(+/+) mice, activated T cells were rapidly cleared from the livers of LFA-1(-/-) mice. Mechanistically, T cells from LFA-1(-/-) mice showed markedly reduced cytotoxicity toward liver cells as a result of impaired, activation-dependent adhesion. Importantly, adoptive transfer of hepatic T cells from LFA-1(+/+) mice, but not from LFA-1(-/-) mice, sensitized LFA-1(-/-) mice to ConA-induced hepatitis. Thus, LFA-1 expression on T cells is necessary and sufficient for T cell-mediated liver damage in vivo. These results provide the first genetic evidence on an adhesion receptor, LFA-1, that has a crucial role in fulminant hepatitis. These genetic data identify LFA-1 as a potential key target for the treatment of T cell-mediated hepatitis and the prevention of liver damage.