Cytokine induction in moDCs by L. amylovorus
The S-layer-carrying L. acidophilus strain NCFM interacts with human DCs eliciting an anti-inflammatory IL-10 response and it promotes the Th2-differentiation of T-cells through DC:s; the S-layer protein has been shown to have a role in this response [12]. Prompted by these findings, we examined the potential of the phylogenetically closely related, S-layer-carrying L. amylovorus strains to induce immune signaling in human DCs. As shown in Figure 5, when tested at the bacteria/DC ratio of 100:1, clear differences between the levels of cytokines induced by the strains were observed. Interestingly, the anti-inflammatory response induced by L. acidophilus NCFM was not observed with the L. amylovorus strains. Instead, our strains typically induced a mixed cytokine response with the release of both proinflammatory (TNF-α, IL-6, IL-1β, IL-12, IP-10/CXCL10) and anti-inflammatory (IL-10) cytokines from human DCs. Furthermore, the strain GRL 1116, which was most potent at inducing proinflammatory cytokines, induced also the highest levels of the anti-inflammatory cytokine IL-10. Analogously, the strain DSM 20531T and GRL 1115 were among the weakest inducers of both pro-and anti-inflammatory cytokines. At the lower MOI values of 1 and 10, no clear induction of any of the cytokines was observed in comparison to the negative control (data not shown).
Figure 5  Cytokine induction in human dendritic cells by L. amylovorus. The extents of induction of TNF-α (A), IL-1β (B), IL-6 (C), IL-10 (D), IL-12 (E) and IP-10/CXCL10 (F) in human monocytic dendritic cells (moDCs) were tested after treating the cells with L. amylovorus strains for 24 hours at the bacteria/DC ratio 100:1. The data are presented as the means and standard deviations from one representative experiment out of three, performed with moDC:s of four donors.

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