Crohn's disease is a type of inflammatory bowel disease that can affect the entire gastrointestinal system, from the mouth to the rectum. However, it most commonly affects the lower part of the small intestine (ileum) and the colon. Crohn's disease is represented by discontinued, chronic transmural inflammation of the gut. It is primarily a consequence of an exaggerated intestinal immune response, changes in the gut microbiota composition and exposure to certain environmental factors in individuals with a genetic predisposition to the disease. The main goals in the treatment of Crohn's disease are to control inflammation and to achieve and maintain remission. For this purpose, there are several therapeutic approaches available, including tumour necrosis factor antagonists (anti-TNF). However, this treatment can be quite expensive and may not be suitable for every patient. Some patients do not adequately respond to the anti-TNF therapy, lose their response over time, experience side effects or develop antibodies against the medication. The primary focus of this doctoral dissertation is on the total serum immunoglobulin G (IgG) N-glycosylation in Crohn's disease. Research in the field of glycobiology has shown that complex oligosaccharides called glycans have a direct impact on IgG effector function. Interestingly, patients with Crohn's disease have been found to have an altered composition of serum IgG N-glycans compared to healthy individuals. Therefore, this doctoral dissertation aims to study how the composition of total serum IgG N-glycans changes over time during anti-TNF therapy with infliximab and adalimumab. Additionally, it aims to explore the predictive potential of total serum IgG N-glycans in therapy response to anti-TNF drugs before initiating treatment. For those purposes, a total of 1513 serum samples were collected from CD patients as a part of the PANTS (Personalised Anti-TNF therapy in Crohn’s disease) study. From that number, 1315 serum samples were used to assess the prediction of therapy response to anti-TNF drugs. Additional 198 serum samples were collected at the second time point to explore the longitudinal change in the composition of total serum IgG N-glycome. The IgG was extracted from serum samples and its N-glycosylation pattern was analyzed using liquid chromatography. The results showed that the anti-TNF treatment in patients with Crohn's disease is associated with significant changes in the composition of total serum IgG N-glycans, regardless of therapy response. Specifically, the level of agalactosylated IgG N-glycans significantly decreased, while mono- and digalactosylated and sialylated glycans increased in their abundance, all of which suggest the reduced proinflammatory potential of serum IgG in patients with Crohn's disease during therapy. Furthermore, the results indicated that the composition of total serum IgG N-glycome at baseline does not hold predictive power to detect future non-responders to anti-TNF therapy.