Different immunomodulatory effects of L. paracasei strains on dendritic cells

The modulation of the immune system is recognized as one of the main mechanisms by which probiotic bacteria exert health-promoting effects. To compare the immunomodulatory properties of L. paracasei strains, we studied their interaction with dendritic cells (DCs) which are important in the earliest bacterial recognition and in determination of the subsequent T-cell responses, playing a pivotal role in both innate and adaptive immunity. The results indicated that all the strains stimulated phenotypic maturation of DCs but they induced different cytokine secretion by DCs and, in particular, a different ratio IL-10/IL-12, which is considered indicative and predictive of in vivo pro- or anti-inflammatory properties. In fact, probiotic strains IMPC 2.1 and LMG P-17806 were characterized by a similar and intermediate ability to induce cytokine secretion, inducing a low pro-inflammatory response, while strain IMPC 4.1 was characterized by very interesting and peculiar anti-inflammatory properties. In contrast, the potentially unsafe strain LMG 23554 showed a very low ability to induce cytokine secretion. Further studies were carried out to ascertain if the immunomodulatory activity of L. paracasei strains on DCs was caused by bacterial metabolites released in the culture medium. Therefore, bacterial culture filtrates were obtained after the growth of the strains in two media generally used for the culture of DCs and their effects on the maturation of DCs and cytokine production were evaluated. An artichoke phenolic extract (APE) was also added to the media before the bacterial growth to reveal its potential activity on immunomodulation of DCs. The results revealed diverse immunomodulatory properties of the culture filtrates depending on the growth medium, on the strain and on the addition of APE; an interesting anti-inflammatory activity of a culture filtrate obtained after the growth of strain IMPC 2.1 in one of the media supplemented with APE was highlighted.