The ultrastructure of hematopoietic stroma on cellulose ester membranes implanted intraperitoneally into Sl/Sld and Sl+/Sl+ mice.

The structural features of hematopoietic stromal elements forming on cellulose ester membranes (CEM) implanted intraperitoneally into hematopoietically impaired, anemic Sl/Sld mice and their normal Sl+/Sl+ littermates were compared by combined light and electron microscopy. The generally thicker, multilayered stroma lining the Sl+/Sl+ CEM implants developed from a bed--a syncytium--of large, highly pleomorphic macrophage-type lining cells whose filopodial extensions exhibited extensive interactions (i.e., nurse cell interactions) with both stromal and hematopoietic elements. In contrast, the thinner stromal layers lining the CEM of Sl/Sld mice formed from a base of dysplastic lining elements. These CEM-lining macrophage-type cells had much reduced cytoplasmic volumes, less extensive interactive surface projections, and an absence of select types of cytoplasmic organelles (e.g., membrane-bound crystalline inclusions). These observations suggest that the reduction of cell layering and, in turn, hematopoietic support activity, is due to an impaired interactive capacity of these elemental lining cells, i.e., pleomorphic macrophagic cell types, in the hematopoietically impaired strain of Sl/Sld mice.