Probiotic administration has been associated with enhanced immune functions in the elderly. Therefore, the selection of new probiotic strains provides an exciting challenge both to research and industry. The intestinal mucosa is considered as one of the biggest immune or¬gans of the body. So, the goal of this study was to evaluate the effect of three strains of bifidobacterium species (Bifidobacterium adolescentis ATCC 15704, B. breve ATCC 15700 and B. longum ATCC 15707) on the count, size, and architecture of the gut associated lymphoid tissue (GALT), besides the histological structure of other lymphoid organs, and the immunohistochemical determination of CD4+ T cells in aged rats. Three groups of aged rats were supplemented each with a different Bifidobacterium strain, and one group was supplied with yoghurt alone (control aged). Two other groups of adult and aged rats were given normal diet. The three strains of Bifidobacteria induced marked improvement in the histological architecture of GALT, thymus and lymph nodes of aged rats, associated with a decrease in the number of mast cells in the thymus. Such changes were more obvious in the lymphoid organs of rats fed B. adolescentis rather than those of B. breve and B. longum groups. Moreover, immunoreactivity of CD4+ T cells was markedly increased in bifidobacteria-treated rats as compared to controls. Conclusively, the decline in the immune system efficiency common in the elderly may be beneficially affected by appropriate probiotic administration.
Key words: Probiotics, bifidobacteria, aging, lymphoid organs, GALT, CD4+
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