Background and objectives Primary Sjögren’s Syndrome (pSS) is an autoimmune disease which affects salivary glands, leading to reduced saliva production and thus severely decreasing the patients’ quality of life. While the pathogenesis remains unclear, several factors are in discussion, e. g., cells of the immune system, such as neutrophils. One function of neutrophils is to expel neutrophil extracellular traps (NETs). NETs usually form in inflamed tissue to immobilize and intrinsically eliminate pathogens. However, if they aggregate, they might obstruct and hence damage ductal gland structures. So, the first hypothesis of this thesis is that due to elevated inflammation levels, high NET concentration is present in the saliva of pSS patients, which influences its viscosity and therefore might be part of the pathogenesis. The focus of the second part of this thesis is on SARS-CoV-2 (severe acute respiratory syndrome coronavirus type 2) and its associated disease COVID-19 (coronavirus disease 2019). SARS-CoV-2 is discussed to cause immune responses similar to those of autoimmune diseases, such as pSS. New antibodies, especially G protein coupled receptor autoantibodies (GPCR AAb), form even in previously healthy individuals post infection. As pSS patients already naturally show multiple autoimmune reactions, our second hypothesis is that previous SARS-CoV-2 infection influences the saliva production in pSS patients due to autoimmune processes. Methods For this study, a cohort of pSS patients, disease control groups consisting of rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) patients, and healthy controls (matched for age and sex) have been recruited. A detailed medical history was taken, including e. g., medication, comorbidities and COVID-19 status. Blood samples of disease control groups and pSS patients were drawn to create a profile of antibodies against secondarily necrotic cells (SNECs), which can be seen as a summary of all antibodies against extractable nuclear antigens (ENA). Furthermore, an ENA antibody profile was compiled using medical records. From every participant of the study, saliva samples were collected. We measured the samples’ rheology, performed neutrophil elastase (NE) and myeloperoxidase (MPO) ELISAs to detect and quantify NETs degradation products, quantified the total protein content through a bicinchoninic acid (BCA) protein assay, and determined the saliva’s cell-free dsDNA content. Results and observations We observed that the leading health issue of pSS patients is oral dryness (xerostomia). Associated with that, the individual’s fluid intake influences salivary production. Furthermore, we observed that the number of mucosal defects and the disease activity are associated with the patient’s amount of smoking. As anticipated because of the mentioned xerostomia, we found decreased saliva volumes in pSS patients. Neither rheology nor salivary composition did differ statistically significant between the groups. However, we found that in all groups the amount of NET degradation products influences salivary rheology to the same extent as the total protein content. Concerning autoimmunity, pSS patients showed the disease-typical ENA antibody profile. In addition to that, their anti-SNEC titers in serum are significantly higher than in RA patients. Pursuing the SARS-CoV-2 autoimmune hypothesis, we found a highly statistically significant increase in saliva volume solely in pSS patients with a history of COVID-19, while there were no differences in saliva composition pre and post infection in any groups. Conclusions As xerostomia has numerous negative effects on the health of pSS patients, they should be encouraged even more to quit smoking because of its negative effects on both mucosa and disease activity. Drinking as the patients’ strategy to relieve xerostomia indeed increases saliva volume measurably. In order to alleviate xerostomia, saliva of healthy individuals can be used as a template to design artificial saliva, since rheology in pSS patients does not differ from the control groups. Furthermore, no elevated amount of NET degradation products was found in pSS patients compared to the other groups. However, NETs contribute to the same extent as total protein content (consisting, e. g., of mucins) to the viscosity of human saliva, which is a new and important finding in salivary research. pSS patients have a highly active autoimmune response, as they not only build the characteristic antibodies anti-SS-A and anti-SS-B and have significant more anti-SNEC antibodies than RA patients, but also show the tendency to express autoantibodies against various other structures. With that being said, we hypothesize that newly formed autoantibodies are the reason for the positive delta saliva volume in pSS patients with a history of COVID-19. More precisely, functional GPCR AAb might be present, activating M3-R, ɑ1-R and β1-R, and thus enhancing salivary secretion. However, further studies are needed to measure how clinically relevant the increase in saliva volume is and how long this effect lasts.
Anne Zeitler (Thu,) studied this question.