Evaluation of the Immunostimulant Effect of Microvesicles of <i>Lactobacillus acidophilus</i> Isolated from Wild Rats

Lactic acid bacteria are components of the gastrointestinal tract microbiota in both humans and animals and are widely used as probiotics. <i>Lactobacillus</i> is the most closely related genus to probiotic activity. It is capable of releasing membrane microvesicles (MVs), whose primary functions include carrying and transmitting antigens to host tissues and modulating host defense responses. In the present study, MVs were isolated from <i>Lactobacillus acidophilus</i> resident in the ileum of free-living rats, and their immunostimulant effect was evaluated in two biological models. MVs were characterized using SDS-PAGE electrophoresis, electron microscopy, and nanoparticle tracking analysis. In the first model, the immunostimulatory effect of MVs was evaluated on ovine abomasal explants, which had been previously stimulated with MVs and then challenged with third-stage larvae of <i>Haemonchus contortus</i>. This resulted in a decrease in the percentage of larval association and favored the migration of inflammatory cells to the infection site. In the second model, the macrophage cell line RAW 264.7 was stimulated with MVs to evaluate the expression of transcripts encoding IL-1β and TNF-α. MVs isolated from <i>L. acidophilus</i> demonstrate immunostimulatory and probiotic effects in the two biological models assessed. This suggested that the MVs possess similar immunostimulatory effects as those reported for the parent bacteria.