Glycosylation is critical for a wide range of biological processes across both normal and disease states. Carbohydrate antigens, for example, are polymeric chains of diverse monomeric sugar molecules that play a fundamental role in the pathogenicity and virulence of many organisms. Moreover, these pathogen‐associated glycan structures can also be found in association with other types of cells, including tumours. These types of glycan commonalities have helped generate critical discoveries in terms of glycan structure, allowing for the development of working hypotheses for their functions, in addition to the development of agents that target or mediate their expression levels. Therefore, through discussion of glycans as antigens, new insights of key molecular and cellular interactions between them and immune cells can be discerned, and the implication of these interactions in health and disease is enhanced. Numerous reviews and even this ELS series have described the structure of carbohydrates and glycans in general. Key Concepts Glycosylation is the most abundant post‐translational modification of proteins. Glycans expand the chemical diversity of the genetic code. Antigens are a collection of epitopes that affects recognition by the immune system. Antigens and immunogens are very different. Molecular mimicry of glycans profoundly affects the pathophysiology of infection and neoplasia. Lectin‐family receptors and antibodies have been used to define carbohydrate antigens. Clustering of epitopes defines glycan antigens better than nonclustered epitopes. Carbohydrate antigens can define danger signals to the immune system through pattern recognition receptors. Clustering associates with different B‐cell populations for processing as immunogens. MHC and T‐cell receptors see atoms in particular arrays, not as a single molecular species – hence cross‐reactivity with zwitterionic carbohydrate structures. While carbohydrate‐based vaccines have been developed, as cancer vaccines they are not as effective. Metabolism is the next frontier to understanding glycan expression patterns.
INTRODUCTION: Percutaneous endoscopic gastrostomy (PEG) is a common procedure for the provision of long term enteral nutrition (1). Indications for PEG tube replacement include tube malfunction, dislodgement, or scheduled exchange (2). Complications of replacement include bleeding, infection, and tube misplacement (3). Gastric outlet obstruction (GOO) is a rare complication seen when the tube is inserted distal to the pylorus or the balloon is overfilled (4). CASE DESCRIPTION/METHODS: An 86-year-old woman with a history of previous stroke necessitating prolonged enteral feeding through PEG presented to the hospital due to a clogged PEG tube. The tube was replaced at bedside via the percutaneous route and gastric fluid was aspirated. The tube was noted to be 2 cm deeper than prior to the procedure. A water-soluble contrast study through the PEG tube was obtained to confirm proper position (Figure 1) which showed contrast within the small bowel. The radiologist concluded the gastrostomy tube was in satisfactory position and tube feedings were resumed. Overnight, the patient experienced several episodes dark emesis. An endoscopy the next morning revealed the gastrostomy tube balloon was inflated in the duodenal bulb causing a GOO (Figure 2). The tube was repositioned in the stomach (Figure 3) and the patient was discharged 4 days later. DISCUSSION: This case illustrates the importance of establishing a standardized approach to the confirmation and documentation of PEG tube replacement. The marker on the replacement tube should be close to that of the previous tube. Notably, resistance to traction at a greater depth than expected may represent post-pyloric placement of the balloon. Finally, when imaging is obtained, fluoroscopy should be performed at an oblique angle and contrast should be observed in the stomach to confirm correct placement.
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