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IL-3 is a glycoprotein cytokine involved in the hematopoietic response to infectious, immunologic, and inflammatory stimuli. In addition, clinical administration of recombinant IL-3 augments recovery in states of natural and treatment-related marrow failure. IL-3 acts by binding to high affinity cell surface receptors present on hematopoietic cells. To determine the site(s) at which IL-3 binds to its receptor, we analyzed a series of interspecies chimera of the growth factor for species-specific receptor binding and biological activity. The results suggest that IL-3 binds to its receptor and triggers a proliferative stimulus through two noncontiguous helical domains located near the amino terminus and the carboxy terminus of the molecule. To corroborate these findings, we have also mapped the binding epitopes of 10 mAb of human or murine IL-3, and have defined four distinct epitopes. Two of these epitopes comprise the amino-terminal receptor binding domain. A third epitope corresponds to the carboxy-terminal receptor interactive domain, and the fourth epitope, apparently not involved in the interaction of IL-3 and its receptor, lies between these sites. And on the basis of sandwich immunoassays using pairs ofthese mAbs, the two receptor interactive regions appear to reside in close juxtaposition in the tertiary structure of the molecule. These results provide a correlation of the structure-function relationships of IL-3 that should prove useful in evaluating the details of IL-3-IL-3 receptor interaction and in the rational design of clinically useful derivatives of this growth factor. (J.

Primary cell cultures enriched in mucin-producing cells and basal cells were established from the trachea of the domestic fowl. Epithelial cells were selectively removed from the trachea after incubation in 0.1% pronase/0.1% EDTA in Moscona's saline. The majority of the ciliated cells were removed during the initial 30 minutes of incubation. After 50 minutes of incubation, aggregates of mucin-producing cells and basal cells were removed in large numbers. The cellular aggregates rapidly attached to a collagen-coated substratum and the cells spread out on the culture surface. The mucin-producing cells retained their AB/PAS-reactive secretory granules. The basal cells replicated and as the culture approached confluency, these cells developed a fine dusting of AB/PAS-reactive material; later, larger secretory granules appeared in the cells. These observations suggest that mucin-producing cells are capable of retaining their AB/PAS-reactive secretory products in primary culture and that basal cells are capable of differentiating into mucin-producing cells in vitro.

Techniques for isolation and culture of fetal lype II alveolar epithelial cells, as well as the morphologic and biochemical characteristics of these histotypic cultures, are described.Type II alveolar epithelial cells can be isolated from fetal rat lungs and grown in an organotypic culture system as described in this review. The fetal Type II cells resemble differentiated rat Type II cells in morphology, biochemistry, and karyotype as they grow in culture for up to 5 weeks. The cells of the mature organotypic cultures form alveolarlike structures while growing on a gelatin sponge matrix. The Type II cells also synthesize and secrete pulmonary surfactant similar in biochemical composition to that produced in vivo. This system has been used to study the effects of hormones on surfactant production and composition. The organotypic model has many potential applications to the study of pulmonary toxicology.