Influence of respiratory syncytial virus infection on the interaction of lung epithelial cells and alveolar macrophages. Investigations using a coculture system

Circulating alveolar macrophages and Type-Il-cells of the lung represent important cells of the respiratory tract with immunomodulatory activities. Alveolar macrophages are the first effector cells of the immune system in the lung to defend bacterial or viral infections. Macrophages influence several cell compartments via direct cell-cell interactions or by secreted products as there are different cytokines or chemokines. Type-ll-pneumocytes are the primary producer ot Surfactant. Additionally, these cells are able to interact with the immune system by secretion of Interleukin-1 (IL-1) and the expression of adhesion molecules as ICAM-1. Our group was interested in the influence of an infection with Respiratory syncytial virus (RSV) on the functions of alveolar macrophages and Typell-cells alone and the interactions between these two cell types. Using in vitro-cultures, it is difficult to examine the influence of one cell compartment of the lung on the other, for this purpose, we established a coculture system using human alveolar macrophages collected from bronchoalveolar lavage and the human cell line A549, representing the characteristics of Type-Il-cells, producing Surfactant, IL-1 and several chemokines i.e. Interleukin-8 (IL-8) and MCP-1. Alveolar macrophages were plated into a 24- well microtiterplate and A549 cells into a tissue culture insert which were placed into the well. To establish the coculture system the movement of the investigated cells through the membrane of the insert was measured to ensure, that no mixing of the cells during the culture occured. We could show, that a pore size of the membrane of 0.45 pm was necessary to inhibit a movement of the cells through the membrane. The cells were infected with RSV either the alveolar macrophages or the A549 cells and after 24 hours, we measured the virus concentration in the culture supernatant. Further, cell culture supernatants were collected at different time points and the concentrations of MCP-1, IL-8 and IL-1 were detected. Infected alveolar macrophages and A549 cells showed an increased secretion of IL-8 in comparison to not infected cells, whereas in the supernatant of cocultured infected alveolar macrophages and A549 cells the strongest increase in the concentration of IL-8 could be demonstrated. The coculture system described is a useful tool to determine interaction between cell compartments without cell-cell-interaction in different situations as there are i.e. infectious diseases.