Fas and Fas ligand expression in the salivary glands of patients with primary Sjögren's syndrome

Role of T-helper type 2 cytokines in down-modulation of fas mRNA and receptor on the surface of activated CD4(+) T cells: molecular basis for the persistence of the allergic immune response

The mechanisms responsible for persistence of T lymphocytes at the sites of allergic inflammation are not completely understood. Activated T cells, usually expressing Fas on their surface, undergo activation-induced apoptotic death, thus limiting the dangerous consequences of a persistent immune reaction. We have previously shown that pulmonary T lymphocytes from untreated asthmatic subjects do not express surface Fas receptors nor do they contain Fas mRNA, yet they display normal levels of Fas ligand. This is not an inherited defect and is confined to mucosal T cells. To gain insights into the mechanism responsible for these findings, we performed a set of experiments with both purified Dermatophagoides pteronyssinus allergen and recombinant human cytokines: interleukin 2 (IL-2), IL-4, IL-5, transforming growth factor beta1, interferon gamma, and granulocyte-macrophage colony-stimulating factor (GM-CSF). In vitro exposure of purified CD4(+) lymphocytes to allergen yielded only transient up-regulation of surface Fas but did not influence susceptibility to Fas-mediated cell death. T-helper type 2 cytokines (IL-4, IL-5, and GM-CSF) had a dose-dependent and specific inhibitory effect on Fas mRNA, suggesting a new fundamental biological role in the survival of inflammatory cells during allergen exposure.

Apoptosis in labial salivary glands from Sjögren's syndrome (SS) patients: comparison with human T lymphotropic virus-I (HTLV-I)-seronegative and -seropositive SS patients

Apoptosis is a type of cell death that occurs during morphogenesis and development of the immune system. One of the mechanisms is mediated through the Fas and Fas ligand (FasL) pathway. To determine the possible involvement of Fas and its ligand in salivary gland destruction, we analysed the appearance of nuclei with DNA fragmentation by using nick end labelling (TUNEL) and the expression of Fas and FasL by immunohistochemistry in labial salivary glands. Furthermore, we compared the features of apoptosis in labial salivary glands between HTLV-I- and HTLV-I+ SS. When the frozen sections of 10 primary SS patients in the absence of anti-HTLV-I antibody were examined, several apoptotic cells were found in the acinar and ductal epithelial cells as well as infiltrated mononuclear cells. Both Fas and FasL were detected in the infiltrated mononuclear cells. Acinar epithelial cells, which are surrounded by FasL+ mononuclear cells, were also double-positive with Fas and FasL, although the expression of FasL was localized at their apical border, suggesting that apoptosis of mononuclear cells was achieved by activation-induced mechanisms through Fas/FasL pathways, and that of acinar epithelial cells was mediated by FasL derived from either acinar epithelial cells themselves or infiltrated mononuclear cells. Interestingly, Fas expression in ductal epithelial cells was localized around the lumen side of the ducts, indicating that FasL secreted from acinar epithelial cells may induce Fas-mediated apoptosis of ductal epithelial cells. We also studied the labial salivary glands from nine SS patients with anti-HTLV-I antibodies. There was no significant difference in the occurrence of apoptotic cells or in the expression of Fas and FasL between HTLV-I+ and HTLV-I- SS patients. It was of note that neither the expression of Fas and FasL nor the presence of apoptotic cells were determined in labial salivary glands from subjects without SS. These findings indicate that Fas-mediated apoptosis in salivary glands could be involved in the pathological manifestations of SS, irrespective of HTLV-I seropositivity.

HIV-associated lymphoepithelial cysts and lesions: morphological and immunohistochemical study of the lymphoid cells

AIMS

To determine the morphology, immunophenotype and bcl-2 protein status of intraepithelial lymphocytes in HIV-positive lymphoepithelial lesions.

METHODS AND RESULTS

Seventeen cases (from adults and children) of HIV-associated parotid and lung lymphoid lesions were examined. In addition, three lymphoepithelial cysts from HIV-negative patients were studied in parallel. Immunohistochemistry was performed on paraffin embedded tissue with the following antibodies: CD20, CD79a, CD3, CD4, CD8, bcl-2, CAM5.2, AE1/3, MIB1, kappa/lambda light chains and EBV-LMP-1. Heavy chain rearrangement was sought by polymerase chain reaction (PCR) in four of the cases. The lymphocytes participating in lymphoepithelial lesions of HIV-positive patients had the morphology of centrocyte-like cells with occasional cells resembling centroblasts. The majority of these cells were of B-cell lineage, but occasional intraepithelial T-cells (CD8 positive, CD4 negative) were also present. T-cells also formed a significant component of the infiltrative lymphoid cells outside the lymphoepithelial lesions. These were mainly CD8 positive, but very occasional CD4-positive T-cells were also noted. None of the cases showed light chain restriction and the four cases did not demonstrate heavy chain rearrangement by molecular biology. The interesting finding was the absence of bcl-2 expression by the intraepithelial lymphocytes. In contrast, the intraepithelial lymphocytes seen in the non-HIV setting were strongly bcl-2 positive. The majority of these were B-cells, and very occasional CD8 and CD4 positive T-cells formed the intraepithelial population.

CONCLUSION

It is postulated that this finding is due to the HIV causing down-regulation of bcl-2 protein.

Bcl-2 family expression in salivary glands from patients with primary Sjögren's syndrome: involvement of Bax in salivary gland destruction

To investigate the molecular mechanism of glandular parenchyma destruction in Sjögren's syndrome (SS), Bcl-2, Bax, Bcl-X, and Bak expression were studied. SS (n = 18) and control salivary glands (n = 6) were examined by immunohistochemistry. Apoptosis was assessed by in situ DNA nick end labeling. Infiltrating mononuclear cells in the SS salivary gland showed elevated Bcl-2. These mononuclear cells expressed increased Bax but did not undergo apoptosis. Both SS and control salivary gland ductal epithelial cells expressed Bcl-2, Bax, and Bcl-X. SS, but not normal, salivary gland acinar cells expressed Bax and underwent apoptosis. These results suggest that elevated Bax expression in SS salivary gland acinar cells may play an important role in the apoptotic pathway. In contrast, Bcl-2 expression in SS infiltrating mononuclear cells and ductal cells may contribute to their survival.

Transfer of human serum IgG to nonobese diabetic Igmu null mice reveals a role for autoantibodies in the loss of secretory function of exocrine tissues in Sjögren's syndrome

The NOD (nonobese diabetic) mouse has been studied as an animal model for autoimmune insulin-dependent diabetes and Sjögren's syndrome. NOD.Igmu null mice, which lack functional B lymphocytes, develop progressive histopathologic lesions of the submandibular and lachrymal glands similar to NOD mice, but in the absence of autoimmune insulitis and diabetes. Despite the focal appearance of T cells in salivary and lachrymal tissues, NOD.Igmu null mice fail to lose secretory function as determined by stimulation of the muscarinic/cholinergic receptor by the agonist pilocarpine, suggesting a role for B cell autoantibodies in mediating exocrine dryness. Infusion of purified serum IgG or F(ab')2 fragments from parental NOD mice or human primary Sjögren's syndrome patients, but not serum IgG from healthy controls, alters stimulated saliva production, an observation consistent with antibody binding to neural receptors. Furthermore, human patient IgG fractions competitively inhibited the binding of the muscarinic receptor agonist, [3H]quinuclidinyl benzilate, to salivary gland membranes. This autoantibody activity is lost after preadsorption with intact salivary cells. These findings indicate that autoantibodies play an important part in the functional impairment of secretory processes seen in connection with the autoimmune exocrinopathy of Sjögren's syndrome.

Apoptosis: a modulator of cellular homeostasis and disease states

In normal epithelial tissue, a homeostatic balance is maintained between cell replication and apoptosis. Disruption of this balance has serious pathological consequences in disease states, such as Sjögren's syndrome, salivary gland degeneration, and cancers. Apoptosis may be modulated by cytokine endogenous factors and exogenous factors. A vast array of environmental compounds, such as differentiating agents and microconstituents found in the diet, initiate apoptosis through a redox signal mechanism. In addition to increasing apoptosis, these redox signals and transient or permanent changes in cellular redox status elevate detoxification enzymes known to protect against many disease states. Clearly a further understanding of the regulation of apoptosis and protective enzyme elevation by exogenous redox signals will lead to the development of future therapeutic strategies against disease.

A novel NOD-derived murine model of primary Sjögren's syndrome

OBJECTIVE

The appearance of autoimmune diabetes prior to autoimmune exocrinopathy in the NOD mouse suggests that it is an excellent model of secondary, but not primary, autoimmune sicca complications. Since the unique major histocompatibility complex (MHC) I-A(g7) expression in NOD mice is essential for the development of insulitis and diabetes in these animals, we investigated exocrine gland function in NOD.B10.H2b mice, which have an MHC congenic to NOD, as a potential model for primary Sjögren's syndrome (SS).

METHODS

Histopathologic manifestations of lymphocytic infiltrates into the pancreas and exocrine tissues were examined by light microscopy. Sera were evaluated for the presence of antinuclear antibodies. Saliva, tears, and gland lysates were evaluated for total volume and protein concentration, the aberrant expression and processing of parotid secretory protein, and cysteine protease activity.

RESULTS

NOD.B10.H2b mice exhibited the exocrine gland lymphocytic infiltration typical of the SS-like disease and dysfunction observed in NOD mice, but without the insulitis and diabetes. These mice additionally expressed elevated levels of cysteine protease activity (a measure of apoptotic activity) and abnormal expression and cleavage of parotid secretory protein in the submandibular tissues.

CONCLUSION

The results of this study suggest that the unique NOD MHC I-A(g7) is not essential for exocrine tissue autoimmunity. Furthermore, the findings indicate that sicca syndrome occurs independently of autoimmune diabetes and that the congenic NOD.B10.H2b mouse represents a novel murine model of primary SS.