The glycocalyx of Lacticaseibacillus paracasei NPB01 presents two different rhamnose-rich polysaccharides with non-equivalent immunomodulating activities.

Lacticaseibacillus paracasei cell wall presents two capsular polysaccharides, CPS-1 and CPS-2, and a teichoic acid. CPS-1 is novel and it presents a branched heptasaccharide repeating unit, with the sequence →6)-α-d-Gal-(1→3)-β-l-Rha-(1→4)-β-d-Glc-(1→3)-α-d-GlcNAc-(1→2)-β-d-Glc-(1→6)-β-d-Glc-(1→ in the linear part to which a β-l-Rha is attached to O-4 of GlcNAc. Regarding CPS-2, its structure was previously reported for L.casei, and it presents the tetrasaccharide repeat 2)-α-l-Rha-(1→2)-α-l-Rha-(1→3)-α-l-Rha-(1→3)-α-d-GalNAc-(1→ as backbone, where the first Rha is substituted with a trisaccharide made of Rha, GlcNAc and Glc, and the third Rha has a Glc as a non-stoichiometric substituent. Preliminary in-vitro immunological analyses disclosed that the two glycans exert different activities. CPS-1 is superior to CPS-2 for the elicitation of IL-33, an interleukin that alerts the immune system to tissue damage or danger. CPS-2 instead is more efficient than CPS-1 in the elicitation of the antimicrobial peptides LL-37 and HBD-2, and it is a strong elicitor of occludin, a protein of the tight junctions relevant for the epithelium integrity. These findings suggest that L.paracasei CPSs play a synergistic and beneficial role in the gut, thus paving the way to studies aimed to examine their mode of action or their exploitation in the prevention and treatment of human gastrointestinal diseases.