Patients with primary Sjögren’s syndrome (pSS) are at increased risk of developing malignant lymphoma. The studies in this thesis aim at broadening our understanding of the association between these two conditions. Germinal centre (GC)-like structures were found in minor salivary gland biopsies taken at the time of pSS diagnosis in 25% of 175 studied patients. Lymphoma development was observed in 86% of the GC-positive pSS patients and 14% of the GC-negative patients. GC-like structures in salivary gland biopsies at pSS diagnosis might identify pSS patients at high risk for later lymphoma development. We used the National Patient Register and the Cancer Register to identify pSS patients with lymphoid malignancy for the following studies. The lymphoma tissues were reviewed and classified according to the WHO classification. In a study of 79 patients with available lymphoma tissues, we identified histopathological and clinical features compatible with IgG4-related disease (IgG4-RD) in one patient (1.3%). Histological features of IgG4-RD in lymphoma tissue in patients with an initial pSS diagnosis seem to be rare but, if present, may indicate underlying IgG4-RD. We identified and compared pSS patients with (n=18/17%) and without (n=87) pre-existing lymphoma at pSS diagnosis and found similar pSS characteristics in both groups. Mucosa-associated lymphoid tissue (MALT) lymphoma in salivary glands was more common in patients with pre-existing lymphoma. The findings support the removal of pre-existing lymphoma as a general exclusion criterion for a pSS diagnosis in classification criteria. Further, the findings suggest an investigation for pSS in patients presenting with MALT lymphoma in salivary glands. We compared the distribution of lymphoma subtypes with a general population reference. Both diffuse large B-cell lymphoma (DLBCL) (32%) and marginal zone lymphoma (MZL) (31%) were common, but only MZL (MALT lymphomas) occurred at an increased relative frequency compared to the general population. Men constituted 15% of 105 pSS patients with lymphoma. Men had a shorter time between the pSS and lymphoma diagnoses and more often had lymphoma in the salivary glands compared with women. Increased awareness of signs of lymphoma in salivary glands already during the first years after pSS diagnosis is justified in men with pSS.

IgG4-related disease (IgG4-RD) is a systemic fibro-inflammatory condition characterised by elevated serum IgG4 and an abundance of IgG4 plasma cells in involved organs. The natural history of disease and pathogenic mechanisms are poorly understood, and are explored in this thesis. The diagnosis of IgG4-RD is a challenge. Evidence to support a serum IgG4 level of 2.8g/l in differentiating IgG4-RD from non-IgG4-RD conditions, a serum IgG1:IgG4 ratio of 0.24 in differentiating IgG4-sclerosing cholangitis from primary sclerosing cholangitis with elevated serum IgG4, and the role of serum IgE in those with a history of allergy and atopy is provided. Furthermore, observational data highlighting new environmental risk factors and disease associations are revealed. Despite being considered a benign corticosteroid-responsive condition, evidence for disease relapse, organ dysfunction and failure, malignancy and mortality in a prospective cohort is shown. Patterns of disease presentation and levels of serum IgG4 and IgE at diagnosis are used to identify those who relapse and develop multi-organ disease. A single antigen initiating disease has yet to be found. Polyclonal IgG4 responses to multiple environmental antigens in IgG4-RD are reported, and evidence against Helicobacter pylori plasminogen binding peptide as a microbial antigen is shown. Novel HLA class II associations, linked to disease susceptibility in a UK cohort provide support for immune-mediated pathogenesis. Gene expression analysis implicates cytokines in driving IgG4 switch and proliferation, chemokines in trafficking and homing of lymphocytes to end organs, complement proteins in the classical and lectin pathways, and members of the TGF-beta pathway as putative immune drivers of disease. Differences in the phenotype of IgG1 and IgG4 B cells in health and IgG4-RD are reported, including responses to complement activation and immune complexes. Finally, elevated IgE levels, the presence of IgE-positive mast cells in involved tissues, and up-regulation of the Fc-Epsilon receptor on the surface of IgG4 cells, support the role of an IgE-mediated response.

Immunoglobulin G4–related disease (IgG4-RD) is a chronic fibrosing inflammatory systemic disorder that has been recognized relatively recently in the medical literature. Little is known about the exact disease pathogenesis and epidemiology. IgG4-RD may be asymptomatic or may have minimal symptoms or involve multiple organs with overt symptoms. The different phenotypes of IgG4-RD can lead to delayed or incorrect diagnosis. We report the case of a 66-year-old male with coal worker’s pneumoconiosis who presented with progressive kidney disease and was diagnosed with tubulointerstitial nephritis due to IgG4-RD. The patient was noted to have progressive kidney disease, skin involvement, worsening interstitial lung disease, complete vision loss in the left eye, and retroperitoneal fibrosis. Serologic workup revealed elevated inflammatory markers, IgG4 and IgG1 levels, and hypocomplementemia. A tissue biopsy helped us establish a definitive diagnosis of IgG4-RD and initiate treatment with glucocorticoids to prevent further progression of kidney disease and other end-organ damage.

© 2017, © 2017 American Federation for Medical Research. A middle-aged man presents with acute pancreatitis of unknown etiology and is found to have a presentation consistent with the diagnosis of type 2 autoimmune pancreatitis (AIP). AIP is a group of rare heterogeneous diseases that are challenging to diagnose. There are 2 types of AIP. Type 1 disease is the more common worldwide than type 2 AIP. While type 1 AIP is associated with IgG4-positive antibodies, type 2 AIP is IgG4 antibody negative. Both types of AIP are responsive to corticosteroid treatment. Although type 1 AIP has more extrapancreatic manifestations and more commonly relapses, this is a case of a patient with type 2 AIP with inflammatory bowel disease and relapsing course.