Introduction: Cardiovascular diseases are the most prevalent cause of human morbidity and mortality worldwideand atherosclerosis is the main underlying cause of it. Probiotics comprise live microorganisms which have beenshown to have beneficial effects on the host when administered in the diet. Since probiotics are known to haveimmunomodulatory effects on the host immune system, these may directly (or indirectly) influence the inflammatoryprocess by which atherosclerotic plaques grow. In this study, Lactobacilli plantarum is used as the probiotic of choiceand its effects on T cell mediated immunity and plasma lipid profile as well as atherosclerotic plaque development arestudied on an experimental animal model of the disease, the ApoE-/- mouse.Material and Methods: The strains were identified by morphological, physical, enzymatic and biochemical assessment.Flow cytometry was used to study T cell subsets. IL-10 levels were determined by ELISA. The effect of L. plantarum onplaque grow was measured using standard histopathological techniques.Results: The survival of L. plantarum along the gastrointestinal tract was confirmed after its isolation from faecalsamples of treated animals. It was shown that L. plantarum is capable of increasing the proliferation of $CD4^+$ $CD25^+$T cells (p=1.4×$10^{-5}$) and the level of IL-10 (p=0.045) and decrease the size of atherosclerotic plaques (p=0.019) in theaortic sinus of the $ApoE^{-/-}$ mouse, without an improvement in cholesterol levels.Conclusion: In conclusion, the findings of this study provide supporting data for the use of L. plantarum as a potentialtherapeutic agent against atherosclerosis.