Lung DCs, due to their localization, must be profoundly in-
fluenced by the epithelial milieu. Thus, we aimed to study
the role of lung epithelial environment, in the function and
differentiation of DCs. Differentiation of DCs was achieved
by culturing monocytes (Mo) with epithelial supernatant
(E-SN) from A-549 epithelial cells stimulated with IL-1βor respiratory syncytial virus (RSV) and compared to mock
condition or Mo cultivated in presence of IL-4 /GM-CSF.
Maturation markers (HLA-DR, CD86, CD80 and CD83),
DCs subset markers, such as myeloid (BDCA-1, BDCA-3 and
CD11c), or plasmacytoid (BDCA-2, BDCA-4 and CD123),
as well as chemo-receptors (CCR3, CCR6 and CCR7) were
analysed. DC functionality was examined by the capacity
of DCs to release cytokines and to present antigens to lymphocytes.
Airway epithelial milieu contained cytokines of
interest among which G-CSF, GM-CSF, IL-6 and IL-15 after
IL-1 β or RSV stimulation. This epithelial supernatant
(E-SN) induced a differentiation of Mo into immature like
DCs, as observed by the upregulation of CD86 and mannose
receptor but maintained expression of CD14. Surprisingly,
mo cultured in mock condition as well as cultured in IL-
1β or RSV-conditioned media induced a transient expression
of BDCA-2, as well as a sustained expression of BDCA-4,
CD123, CD11c and CCR6 at day 2. Interestingly, these DCs
maintain an immature phenotype after stimulation with
TLR-4 ligand (LPS), and TLR-3 ligand (poly I:C) maintaining
a low expression of CD80, CD83 and no expression of
CD86 and CCR7. Furthermore, the EC-conditioned media
has kept an important immunosuppression inhibiting the
release of IL-12 and TNF-α, but do not inhibit the release
of IL-6 and IL-10. EC-conditioned DCs still maintain the
release of IFN-α and IFN-λ after TLR-9 stimulation. Functionally,
E-SN-DCs were able to induce a strong autologous
mixed lymphocyte reaction, however, they failed to present
exogenous antigens such as tetanus toxoide. Lung epithelial
supernatants were shown to induce regulatory features in
DCs, with an important regulatory function. The epithelium
not only seem to keep the cells in their environment avoiding
migration of DCs to the lymph-nodes, but also during
infection maintain an important anti-inflammatory profile
by the release of IL-10 and shutting down the release of IL-
12 and TNF-a. Understanding the mechanism by which the
epithelium control tolerance or immunity is essential for the
development of a successful vaccine.
Support for this work was provided by SNF grant : 3200-
065352.01