The initial characterization of a thymus factor chemotactic to bone marrow cells.

Thymus supernatants were produced by cluturing minced newborn CBA/J mouse thymuses in serum-free media for 48 h. Supernatants thus obtained were chemotactic to a subset of bone marrow cells as assessed in blind well chambers, and enriched for immature lymphoid cells in the migrating cell population. The enriched population of cells was shown to be capable of homing to the thymus of an irradiated mouse in vivo in a significantly higher percentage than nonmigrated bone marrow cells. In this report, initial characterization of the factor(s) responsible for this in vitro migration is presented. Several well studied thymic factors were compared with the thymus supernatants for their ability to induce migration of bone marrow cells in vitro. Thymulin (FTS-Zn), FTS, and TP-5 (the pentapeptide fragment of thymopoietin) were used. None of these factors demonstrated chemotactic properties in the migration assay using concentration ranges in which other in vitro activities have been observed. The chemoattractive activity of the supernatant was unaltered by ultracentrifugation. The effects of temperature on the chemotactic properties of thymus supernatant were examined, and a fifty percent decrease in observed migration occurred with thymus supernatant heated to 100 degrees C for 1 h. In addition, incubation of the supernatant for 1 h at 37 degrees C with chymotrypsin, but not with trypsin, inhibited migration, presumably by inactivation of the active factor. Using Amicon microconcentrators, the supernatant was separated into several fractions based on molecular weight. Initial data suggest that the active fraction is in the less than 10,000 mw range.