The fatality of highly pathogenic avian influenza H5N1 infection is associated with severe forms of acute lung injury (ALI) where excessive cytokine induction contributes to damage of the epithelium barrier, causing accumulation of protein-rich fluid in the alveolar airspace. This pulmonary flooding compromises gaseous exchange and ultimately ends in respiratory failure. To date, there are no effective treatments available for ALI. Umbilical cord-derived mesenchymal stromal cells (UC-MSCs) are a distinctive neonatal population of multipotent cells, which possess well-known immunomodulatory and trophic properties and thus display therapeutic potential in repairing the injured lung.
Using an in vitro lung injury model comprising of primary human alveolar epithelial cells (AEC) cultured on transwell inserts and UC-MSCs in the basolateral well, we studied the paracrine effects of UC-MSCs on various parameters of H5N1-associated lung injury; host inflammatory responses, alveolar fluid clearance (AFC), and protein permeability (APP). Cells were infected with highly pathogenic influenza H5N1 (A/HK/483/97) virus at MOI 0.1 or 2. At 24 hours post-infection (24hpi), mRNA expression of inflammatory cytokines were measured by qPCR. The rate of AFC and APP was determined by changes in concentration of FITC-conjugated Dextran.
Major pro-inflammatory cytokine expression (IFN-beta, IL-6, IP-10, MCP-1, RANTES) of H5N1-infected AECs was significantly reduced in the presence of UC-MSCs at 24hpi compared to no UC-MSC treatment. Anti-inflammatory cytokine (IL-4, IL-10, IL-11, IL-13 and IL1-RA) responses were also greater when H5N1-infected AECs were incubated with UC-MSCs. Furthermore, UC-MSCs effectively restored impaired AFC and APP of infected AECs compared to PBS controls.
Here we have demonstrated that UC-MSCs are potent in attenuating several mechanisms of H5N1-induced ALI in vitro such as regulating inflammatory mediators associated with infection and may be a promising novel therapeutic option towards the treatment of severe human influenza disease.