Impact of the Probiotic Strain Lactobacillus rhamnosus K/AR-08 on the Course of Experimental Allergic Encephalomyelitis and Inflammatory Changes in the Intestine of Rats

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system, accompanied by inflammatory demyelination and neurodegeneration. In recent years, the role of the microbiota–gut–brain axis in its pathogenesis has been actively studied. Experimental allergic encephalomyelitis (EAE) is a valid model of MS in rodents. Although structural and immunological changes in the intestine have been described in EAE, the impact of probiotic strains on the course of disease progression and the morphological manifestations of intestinal inflammation in this model has been insufficiently investigated. The study was aimed to evaluate the effect of an extended-course administration of the probiotic strain Lactobacillus rhamnosus K/AR-08 on EAE severity dynamics in rats, as well as on eosinophilic infiltration of the mucosa and mitotic activity of the intestinal epithelium. The study was carried out on 63 sexually mature female Wistar rats divided into three groups: intact control (n = 5), EAE (n = 30), and EAE treated with L. rhamnosus K/AR-08 (n = 28). EAE was induced by a single subcutaneous injection of spinal cord homogenate emulsified in complete Freund’s adjuvant (CFA). Histological analysis of the intestine included assessment of eosinophilic infiltration of the mucosal lamina propria and counting of the mitotic index of crypt epithelial cells. The extended-course administration of L. rhamnosus K/AR-08 led to a reduction in symptom severity and a shortening of disease duration. Probiotic treatment attenuated eosinophilic infiltration of the lamina propria of the small intestinal mucosa while maintaining mitotic activity of crypt epithelial cells. In the large intestine, the effects of the probiotic were less pronounced and manifested only at the peak of the disease as a reduced eosinophilic infiltration, whereas no significant effect on the mitotic activity of colonocytes was observed. Thus, the extended-course administration of L. rhamnosus K/AR-08 prevents the development of severe forms of EAE, shortens the duration of the disease, and exerts a protective effect on the intestinal mucosa, predominantly at the small-intestinal level and associated with attenuation of eosinophilic infiltration, as well as maintenance of mitotic activity of epithelial cells.