THY1-(-(-) LUNG FIBROSIS SUBPOPULATIONS IN LEW AND F344 RATS() AND THY1)

Appreciation of the potential of fibroblasts as effector cells in infl ammation has led to the recognition of fibroblast subpopulations, the most stable of which are the Thy1 (+) and Thy1 (-) subpopulations in m ouse lung fibroblasts, We investigated the presence of Thy1 (+) and (- ) fibroblasts in rats, comparing the percentage in primary cultures fr om rats with different susceptibility to fibrosis, and whether the cha racteristics were similar in mice and rats, and between normal and fib rotic rats lungs. Using primary cultures of rat fibroblasts obtained b oth from normal and fibrotic lungs, we analysed the percentage of Thy1 (+) and (-) fibroblasts by fluorescence-activated cell sorter (FAGS) analysis, We sorted the fibroblasts to evaluate immune region associat ed antigen (Ia) expression, which tends to be raised in tissues involv ed in inflammation, and other characteristics. We found that Thy1 (+) and (-) fibroblasts: 1) are distinct subpopulations in rat lungs; 2) a re found in different proportions in rat strains with different propen sity towards lung fibrosis; and 3) have similar but not identical char acteristics in mice and rats, We also found that bleomycin-induced fib rosis increases the percentage of Ia expression in Thy1 (-), but not T hy1 (+) fibroblasts. The presence of these stable fibroblast subpopula tions in multiple species, and the fact that these fibroblasts differ in their response to a fibrosing agent, suggests the importance of con sidering fibroblast subpopulations in development and disease.