All roads lead to IgA: Mapping the many pathways of IgA induction in the gut

IgA Antibodies to Bovine Serum Albumin in Adult Patients with Celiac Disease

This study investigated the IgA antibodies targeting bovine serum albumin (BSA) in 27 adult celiac disease (CD) patients adhering to a gluten-free diet (GFD), compared to 123 controls (including individuals with autoimmune disorders, those with gastrointestinal cancers, and healthy donors). Serum samples were evaluated using a multiplex assay based on a microarray comprising 66 immobilized antigens, including autoantigens associated with autoimmune diseases, different albumins, cytokines, and inflammatory markers. Elevated IgA-BSA levels were detected in 22% of CD patients versus 3.25% of controls. IgA-BSA did not cross-react with milk proteins like casein, β-lactoglobulin, and γ-globulin, nor with autoantigens and human albumin, ruling out autoimmunity against self-proteins. The observed cross-reactivity with porcine albumin suggests that antibodies target epitopes shared by bovine and porcine albumin. Increased IgA-BSA levels may interfere with immunoassays performed using BSA as a stabilizer, necessitating protein-free buffers to avoid false results when testing CD patients. Elevated IgA-BSA levels may reflect ongoing gut barrier dysfunction in CD patients on a GFD, allowing dietary proteins like BSA to trigger immune responses. This study identifies a novel immune response in CD patients on a GFD, emphasizing the need for tailored diagnostic approaches (BSA-free assays) and further research into the clinical and dietary implications of IgA-BSA elevation.

Macronutrients as Regulators of Intestinal Epithelial Permeability: Where Do We Stand?

The intestinal barrier function (IBF) is essential for intestinal homeostasis. Its alterations have been linked to intestinal and systemic disease. Regulation of intestinal permeability is key in the maintenance of the IBF, in which the intestinal epithelium and tight junctions, the mucus layer, sIgA, and antimicrobial peptides are important factors. This review addresses the concept of IBF, focusing on permeability, and summarizes state-of-the-art information on how starvation and macronutrients regulate it. Novel mechanisms regulate intestinal permeability, like its induction by the normal process of nutrient absorption, the contribution of starvation-induced autophagy, or the stimulation of sIgA production by high-protein diets in a T-cell-independent fashion. In addition, observations evidence that starvation and protein restriction increase intestinal permeability, compromising mucin, antimicrobial peptides, and/or intestinal sIgA production. Regarding specific macronutrients, substantial evidence indicates that casein (compared to other protein sources), specific protein-derived peptides and glutamine reinforce IBF. Dietary carbohydrates regulate intestinal permeability in a structure- and composition-dependent fashion; fructose, glucose, and sucrose increase it, while nondigestible oligosaccharides (NDOs) decrease it. Among NDOs, human milk oligosaccharides (HMOs) stand as a promising tool. NODs effects are mediated by intestinal microbiota modulation, production of short-chain fatty acids, and direct interactions with intestinal cells. Finally, evidence supports avoiding high-fat diets for their detrimental effects on IBF. Most studies have been carried out in vitro or in animal models. More information is needed from clinical studies to substantiate beneficial effects and the use of macronutrients in the treatment and prevention of IBF-related diseases.