Michael G. Humphreys-Beher

Evidence for antimuscarinic acetylcholine receptor antibody–mediated secretory dysfunction in NOD mice

OBJECTIVE Antibodies directed against general and specific target-organ autoantigens are present in the sera of human patients and animal models with autoimmune disease. The relevance of these autoantibodies to the disease process remains ambiguous in most cases. In autoimmune exocrinopathy (Sjögrens syndrome), autoantibodies to the intracellular nuclear proteins SSA/Ro and SSB/La, as well as the cell surface muscarinic cholinergic receptor (M3) are observed. To evaluate the potential role of these factors in the loss of secretory function of exocrine tissues, a panel of monoclonal and polyclonal antibodies was developed for passive transfer into the NOD animal model. METHODS Monoclonal antibodies to mouse SSB/La, rat M3 receptor, and a rabbit polyclonal antiparotid secretory protein antibody were obtained for this study. These antibody reagents were subsequently infused into NOD-scid mice. Saliva flow rates were subsequently monitored over a 72-hour period. Submandibular gland lysates were examined by Western blotting for alteration of the distribution of the water channel protein aquaporin (AQP). RESULTS Evaluation of the secretory response indicated that only antibodies directed toward the extracellular domains of the M3 receptor were capable of mediating the exocrine dysfunction aspect of the clinical pathology of the autoimmune disease. In vitro stimulation with a muscarinic agonist of submandibular gland cells isolated from mice treated with anti-M3 antibody, but not saline or the isotype control, failed to translocate AQP to the plasma membrane. CONCLUSION These findings define a clear role for the humoral immune response and the targeting of the cell surface M3 signal transduction receptor as primary events in the development of clinical symptoms of autoimmune exocrinopathy. Furthermore, the anti-M3 receptor activity may negatively affect the secretory response through perturbation of normal signal transduction events, leading to translocation of the epithelial cell water channel.

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 Sjögrens 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.

Utilization of the non-obese diabetic (NOD) mouse as an animal model for the study of secondary Sjögren's syndrome.

Sjogren’s syndrome (S.S.) in the human patient population is an autoimmune inflammatory disease presenting clinical symptoms of xerophthalmia and xerostomia1. This condition predominantly affects women. Most diagnoses of S.S. is made in association with autoimmune connective tissue diseases such as rheumatoid arthritis or systemic lupus erythematosus.2 However, it can also be obseved as an isolated phenomenon, described as primary S.S.

An Alternative Perspective to the Immune Response in Autoimmune Exocrinopathy: Induction of Functional Quiescence Rather Than Destructive Autoaggression

Sjögrens syndrome is characterized by dryness of the eyes and the mouth due to mononuclear cell infiltration of the lacrimal and salivary glands. The aetiology is unknown but autoimmunity is considered to play a significant role in the pathogenesis. Recent studies have focused on the fact that tear and salivary flow involves an entire functional system that includes the mucosal surfaces with adnexes (the site of inflammation), efferent nerve signals sent to the midbrain (lacrimal and salivary response region), and afferent neural signals from the brain to the acinar/ductal epithelial structures in the gland. Mononuclear cell infiltration in exocrine glands can lead to glandular destruction, suggested to be mediated through apoptosis. However, the functional impairment of exocrine glands could be regulated by cytokines and/or antibodies against the muscarinic M3 receptor by inhibiting the neural stimulation of the residual glands. This review discusses the possibility that the pathogenesis of Sjögrens syndrome comprises aberrant immune‐mediated neuro‐hormonal events.

Characterization of the Changing Lymphocyte Populations and Cytokine Expression in the Exocrine Tissues of Autoimmune Nod Mice

NOD mice develop chronic lymphocytic invasion of the pancreas, submandibular, and lacrimal glands leading to loss of insulin secretion, salivary flow, and tear production. In this study, we have used flow cytometric analyses and RT-PCR to track glandular lymphocyte populations and cytokine expression spanning the initiation of autoimmune infiltration through the development of widespread autoimmune destruction of the salivary and lacrimal glands of NOD mice. Results demonstrate a predominance of CD4+ to CD8+ lymphocytes and a similar predominance of T-cells versus B-cells in both the submandibular and lacrimal gland infiltrates. A temporal increase in memory (CD3+CD45RBlo) T-cells was also detected; however, naive (CD3+CD45RBhi) T-cell populations as well as a CD3+, CD4-/CD8- double negative population were also present. In addition, a skewing of the TCR Vbeta repertoire toward Vbeta6+ and Vbeta8+ lymphocytes was evident in both glandular infiltrates. Analyses of cytokine mRNA expression in the submandibular glands demonstrated an increase between 12 and 16 wk of age of several proinflammatory cytokines including IL-1beta, IL-6, IL-7, IL-10, IFNgamma, TNFalpha, and inducible Nitric Oxide Synthase (iNOS). IL-4 synthesis was notably absent in both tissues. Cytokine mRNA transcripts detected in lacrimal tissue were similar to those seen in the submandibular glands but appeared both earlier and more intensely. These findings depict the progressive development of autoimmune exocrinopathy and can be used as a foundation to explore the similarities and potential differences in the immunopathogenic lesions of several distinct tissues within the same host.

IL-4-Dependent Effector Phase in Autoimmune Exocrinopathy as Defined by the NOD.IL-4-Gene Knockout Mouse Model of Sjogren's Syndrome

NOD mice manifest many features of autoimmune exocrinopathy (Sjögrens syndrome), a disease generally characterized by a chronic, progressive immunological attack against the exocrine tissues of the salivary and lacrimal glands. Previous studies using the NOD congenic partner strain, NOD.Igμnull, defined an important role for B lymphocytes in the development of xerostomia, implicating autoantibodies reactive with the acetylcholine muscarinic receptor (M3R) as the possible effector mechanism. In the present study, we have examined the impact of the cytokine, interleukin (IL)‐4, on autoimmune exocrinopathy by using the IL‐4 gene knockout (KO) NOD mouse strain, NOD.IL‐4−/−. Despite manifesting the physiological aberrations and marked leukocytic infiltration of the salivary glands characteristic of autoimmune xerostomia in NOD mice, the NOD.IL‐4−/− mice do not develop xerostomia. However, NOD.IL‐4−/− mice that received adoptively transferred T lymphocytes derived from NOD.Igμ−/− mice progress to xerostomia, thereby reversing the defect. While progression or lack of progression to xerostomia correlated with the ability of the NOD.IL‐4−/− mice to express detectable anti‐M3R autoantibodies, the precise mechanism of how IL‐4 influences the development of autoimmune xerostomia remains speculative.

The role of apoptosis in the initiation of the autoimmune response in Sjogren's syndrome

The aetiopathogenesis of autoimmune disorders has remained elusive despite much effort over many years devoted to possible genetic, viral and hormonal mechanisms [1,2]. Although genes, viruses, and sex hormones are no doubt involved, a key factor analogous to the role of oncogenes in cancer has escaped detection in autoimmunity. Apoptosis, or programmed cell death (PCD), a critical mechanism preserved throughout evolution to assure both morphologic modelling in fetal life as well as elimination of damaged cells throughout life, may be that key factor in development of autoimmunity [3].

Detection of insulin and insulin-like growth factors I and II in saliva and potential synthesis in the salivary glands of mice: Effects of type 1 diabetes mellitus

The salivary glands of mammals synthesize and secrete a number of peptide growth factors that play important roles in cell/tissue homeostasis and embryonic development. Using a radioimmunoassay, insulin, insulin-like growth factor-I (IGF-I) and insulin-like growth factor-II (IGF-II) were detected in saliva from mice. Unlike epidermal growth factor (EGF), there was no sexual dimorphism in the concentrations of the insulin growth factor family. Immunohistochemical localization of IGF-I and IGF-II was confined to the duct cells of both the parotid and the submandibular glands. Reverse transcriptase-polymerase chain reaction amplification of total RNA from parotid and submandibular glands confirmed the presence of all three hormone/growth factor mRNAs in both glands. The levels of insulin and IGF-I were higher in saliva from an animal model for autoimmune type 1 diabetes, the non-obese diabetic (NOD) mouse, than in a second inbred strain, BALB/c. In contrast, the IGF-II levels were decreased relative to the BALB/c strain. With the onset of diabetes in NOD mice, insulin levels declined, while IGF-I and IGF-II levels showed trends toward lower levels of these growth factors when compared with non-diabetic animals. These changes were reflected in the concentrations from parotid and submandibular gland cell lysates.

Abnormal organogenesis in salivary gland development may initiate adult onset of autoimmune exocrinopathy

Objectives: Salivary gland organogenesis was evaluated in NOD mice, an animal model for autoimmune exocrinopathy, to determine when disease onset is first present in the target tissues. Methods: Submandibular glands were removed for histological, immunohistochemical and biochemical evaluation from neonatal NOD and congenic strains as well as healthy control C57BL/6 mice. Results: Histomorphological analyses of neonatal submandibular glands, the primary target for autoimmune exocrinopathy at 1 day postpartum, revealed delayed morphological differentiation during organogenesis in autoimmune-susceptible NOD mice when compared to nonsusceptible C57BL/6 mice. Acinar cell proliferation was reduced, while expression of Fas, FasL and bcl-2 were increased. Acinar cell proliferation was reduced, while expression, of Fas, FasL and bcl-2 were increased. Throughout the preweaning period (21 days) submandibular glands from NOD and NOD congenic strains aberrantly expressed an increased matrix metalloproteinase (MMP)-2 and MMP-9 activity. Substitution of two susceptibility alleles (Idd3 and Idd5) in NOD mice resulted in an hierarchical and additive reversal of delayed organogenesis, elevated MMP-9 activity, and aberrant expression of parotid secretory protein. Discussion: NOD-derived mice whose submandibular glands showed normal organogenesis did not progress to develop autoimmune exocrinopathy. Altered organogenesis of target tissue may therefore provide a cellular microenvironment capable of activating autoimmunity.

New concepts for the development of autoimmune exocrinopathy derived from studies with the NOD mouse model.

The non-obese diabetic (NOD) mouse is now recognized as an appropriate model to study autoimmune exocrinopathy prevalent in human Sjögrens syndrome patients. With increasing age, NOD mice undergo histopathological changes similar to human Sjögrens syndrome patients, but more importantly, exhibit the same clinical manifestation of declining exocrine tissue secretory function. Studies with the immunodeficient NOD-scid mouse have provided evidence for the temporal loss in the expression of several major salivary proteins and a decreased presence of acinar cells in salivary tissues. The diminished presence of acinar cells is accompanied by an increase in the enzymes associated with apoptosis in the absence of T- and B-lymphocytes. Despite these alterations, NOD-scid mice, unlike NOD mice, do not lose secretory function. Recent analyses of a second congenic NOD strain, the NOD.Igmnull, which lacks B-lymphocytes, indicate the histological presence of a T-cell infiltrate of the exocrine glands, increased caspace activity and induction of the biochemical alterations in protein expression observed in NOD and NOD-scid mice. NOD.Igmnull mice also do not lose secretory function, but can be manipulated to generate a reduced secretory response following the infusion of IgG fractions from autoimmune NOD mice or Sjögrens syndrome patients. These observations, in the absence of components of the adaptive arm of the immune system, have given rise to the concept that autoimmune exocrinopathy develops in two phases. The initial phase is lymphocyte independent and occurs as a consequence of an innate error in exocrine tissue homeostasis or differentiated function. The subsequent tissue specific immunological attack, generated in part by B-cell autoantibodies, is responsible for the loss of secretory function. Our preliminary observations in both NOD mice and Sjögrens syndrome patients is that antibody directed against the cell surface muscarinic/cholinergic receptors appears to play an important part in the onset of clinical disease.