The shift of fluorescence peak obtained for LL-mInlA+ in FACS analysis was significantly higher as compared to NZ9000 strain thus confirming successful surface expression of mInlA on L. lactis.
Other invasins, from Gram-positive bacteria, such as this website InlA or FnBPA, have already been successfully expressed in L. lactis confirming that the signal peptide for secretion and the anchoring signal are well recognized by the L. lactis machinery. Production of invasins from Gram-negative bacteria, such as Yersinia pseudotuberculosis invasin at the surface of L. lactis has never been successful (Denis Mariat, personal communication). The invasivity was assessed by gentamicin assay in non-differentiated E-cadherin expressing human epithelial cell line Caco-2 cells. This experiment
showed that LL-mInlA+strain is 1000-fold more invasive than NZ9000 strain. Wollert and collaborators (2007) observed a 2-foldincrease in the adhesion and invasion efficiency of L. monocytogenes strain producing mInlA compared to wild-type listeria expressing native InlA by using gentamicin-protection-invasion assays in Caco-2 cells [30]. A confocal image taken after gentamicin assay showed clearly that LL-mInlA+ is capable of adhering to and entering in non-differentiated Caco-2 cells. find more The preferential distribution of recombinant bacteria at the periphery of the Caco-2 cell islets can be explained by the fact that E-cadherin is accessible only at the periphery. A similar type of bacterial distribution, around the Caco-2 cell islets, was previously observed when Caco-2 cells were co-incubated with LL-FnBPA+[25]. LL-mInlA+ and LL strains were then transformed with pValac: BLG plasmid, co-incubated with Caco-2 cells and BLG expression was followed 72 h later
by ELISA. BLG was detected in the cytoplasmic fraction of Caco-2 cells which were co-incubated with noninvasive and invasive strains carrying pValac: BLG. This data confirms prior observations that even noninvasive L. lactis can transfer functional plasmids to Caco-2 cells [23]. Cells were also capable of secreting the allergen, which is an interesting characteristic facilitating antigen uptake see more and presentation by professional APCs through cross-priming pathways [1]. The use of LL-mInlA+ improved BLG expression around ten times compared to noninvasive strain. Our hypothesis is that invasive lactococci can enter in higher numbers inside epithelial cells and thus deliver more plasmids. Noninvasive and invasive L. lactis, carrying pValac: BLG or not, were orally administered for 3 consecutive days in BALB/c mice. On the fourth day, enterocytes from the small intestine were isolated and BLG production was measured by enzyme immunoassay (EIA). Isolated enterocytes from mice administered with invasive LL-mInlA+BLG produced the same amount of BLG as compared to mice immunized with noninvasive LL-BLG. Thus, we confirmed that noninvasive lactococci are able to transfer a functional plasmid in vivo in mice [27].