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This paper describes the isolation and partial characterization of a collagen cell attachment protein from the spent culture medium of rat hepatoma cells. When compared with serum fibronectin, this attachment protein differed in several biochemical parameters. The hepatoma attachment protein was partially purified by adsorbing and eluting from an inorganic gel, magnesium oxide. Cell adhesive activity may routinely recovered at levels of 10 to 30%, and a 2000-fold purification was attained. The hepatoma attachment protein was shown to be sensitive to trypsin and chymotrypsin, to be heat inactivated at 61 degrees, to have a molecular weight of 58,000, to have an isoelectric point of 4.1, to show an electrophoretic mobility on cellulose acetate of approximately one-half that of fibronectin, and not to cross-react with antifibronectin antisera.

Adult male mice were treated with various doses of 6-hydroxydopamine in order to assess the effects of this drug upon thymic dependent immunity. A consistent decrease in primary antibody titers to sheep erythrocytes was observed following treatment with this drug. Serum levels of thymosin alpha 1 were increased by day three after 6-OHDA with a return to normal by day five. Thymocyte terminal deoxynucleotidyl transferase changes were biphasic with an initial decrease after 6-OHDA followed by an increase. Changes in mitogen responsiveness were observed but were not consistently reproducible. Involvement of both catecholamines and corticosteroids in bringing about these observed changes was discussed.

We describe the generation of a monoclonal anti-idiotypic (anti-id) antibody directed against affinity purified rabbit antibodies (id) to recombinant human IL-2. This monoclonal antibody, 6A12, has the ability to inhibit the neutralization of IL-2 activity by the id, suggesting that it may bind at or near the IL-2 neutralizing site on the id. 6A12 exhibits IL-2 agonist activity on PHA-activated human T cells. The purified IgG of 6A12 is also shown to bind to a purified soluble recombinant p55 subunit of the IL-2 receptor. Furthermore, purified 6A12 shows inhibition of IL-2 activity in an IL-2 dependent mouse T cell line (CTLL) and this inhibition can be reversed by excess IL-2. These results suggest that although 6A12 may not be an exact 'internal image' of the receptor binding site of IL-2, it may bind to at least the P55 subunit of the ligand binding site on the high affinity IL-2 receptor complex.