Alveolar Accumulation of Hyaluronan and Alveolar Cellular Response in Bleomycin-induced Alveolitis

Hyaluronan (HA) accumulating in the alveolar interstitial tissue of rats injured by a single intratracheal instillation of bleomycin has been visualized histologically and assayed. HA was present already by Day 1 after bleomycin treatment, increased to a maximum value on Days 3 and 7 and then declined. A time-dependent relationship between this early connective tissue response and the invasion of inflammatory cells in the alveolar tissue was apparent. The dominating invading cells by Day 1 were granulocytes showing positive staining for the monoclonal antibody OX-42 reflecting the C3b receptor. The numbers of macrophages expressing class II antigens started to increase on Day 1, reaching a maximum on Days 3-7 and then declined. Macrophages were the dominating OX-42+ cells by Day 7. The appearance of W3/13+ cells ("pan-T-lymphocytes") showed a similar pattern to that for the class II expressing macrophages. The number of cells expressing CD4 antigen increased until Day 3 and levelled off on Day 30 whilst the largest number of cells expressing CD8 antigen was seen on Day 30. Few cells expressing B-cell phenotype outside lymph nodules were identified. Alveolar lining epithelial cells, probably epithelial type II cells, expressed class II antigens by Days 3-14. The time-related accumulation of HA and the appearance of T-cells, macrophages and granulocytes expressing signs of activation suggests that these cells may be involved in the early connective tissue response of the lung injured by bleomycin.