Abstract
The ability of the immune system to respond to different pathogens throughout life requires the constant production and selection of T cells in the thymus. This immune organ is very sensitive to age, infectious processes and nutrition disorders (obesity and malnutrition). Several studies have shown that the incorporation of some probiotic bacteria or probiotic fermented milk in the diet has beneficial effects, not only at the intestinal level but also on distant mucosal tissues, improving the architecture of the thymus in a malnutrition model. The aim of the present study was to determine whether supplementation with the probiotic strain Lactobacillus casei CRL 431 and/or its cell wall could improve body weight, intestinal microbiota and thymus structure and function in both obese and aging mice. We evaluated probiotic administration to BALB/c mice in 2 experimental mouse models: obesity and senescence, including mice of different ages (21, 28, 45, 90 and 180 days). Changes in thymus size and histology were recorded. T-lymphocyte population and cytokine production were also determined. The consumption of probiotics improved the cortical/medullary ratio, the production and regulation of cytokines and the recovery of mature T-lymphocyte populations of the thymus in obese and old mice. Probiotic incorporation into the diet could not only modulate the immune system but also lead to thymus function recovery, thus improving quality of life.
Highlights
The thymus is a primary lymphoid organ present in all vertebrates [1] and is responsible for the development of self-restricted, self-tolerant and immunocompetent T cells
Feeding mice an high-fat diet (HFD) induced an increase in the body weight of obese control mice, with their weight being significantly different from the normal control mice at week 9, where the OC mice reached the peak of their body weight
We observed a significant reduction in body weight in the mice that received the HFD and the supplementation with the probiotic strain suspension at week 10 compared with the OC mice (*** p < 0.001), being a little lower than the normal control
Summary
The thymus is a primary lymphoid organ present in all vertebrates [1] and is responsible for the development of self-restricted, self-tolerant and immunocompetent T cells. The maturation process of T lymphocytes involves different stages of proliferation and differentiation that depend on the instructions from the specialized thymus microenvironment [2]. Thymocytes that have a TCR with specificity for their own antigens (self-reactive lymphocytes) are negatively selected and eliminated by apoptosis. The positive selection induced in the thymic cortex promotes the migration of positively selected thymocytes to the medullary region. This migration of thymocytes is driven by chemokines produced mainly by the epithelial cells of the thymus, with chemokine CCRL7 being essential in this process [7,8,9,10]
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