Search

Flow cytometry was used to demonstrate that cultured human melanoma BRO cells expressed membrane-bound tumour necrosis factor-alpha (TNF-alpha) and were able to release TNF-alpha upon treatment with glucosaminylmuramyl dipeptide (GMDP). The released TNF-alpha was shown to prime melanoma cells, previously unable to respond to GMDP by increasing expression of melanoma-associated antigens, making them sensitive to GMDP treatment.

T-cell growth factor (interleukin 2) was partially purified from the conditioned medium from Con A-stimulated rat splenocytes. It had the molecular weight of 23,000 according to gel filtration and in the range of 17,000-18,000 daltons according to PAGE in the presence of SDS. The molecular forms of IL 2 exhibited isoelectric points (pI) of 5.4-5.8 (major peak), 4.3-4.5 and 6.5-6.8 (minor peaks). T-cell growth-promoting activity was remarkably stable to temperature, pH, SDS and 2-ME treatments. Rat IL 2 did not bind to immobilized Con A, WGA, RC 1, and fucose-binding protein. The conditioned medium also contained the inhibitor of IL 2-dependent T-cell proliferation.

The production of interleukin 2 by rat splenocytes, stimulated with Con A in serum-free medium, was studied. Under optimal conditions the stimulation in serum-containing and serum-free media resulted in identical interleukin 2 titers. The addition of phorbol myristate acetate prior or simultaneously with Con A did not augment interleukin 2 production. In contrast, preincubation of lymphocytes in serum-free medium for 24-36 hrs brought about a 8-10-fold increase of interleukin 2 titer. The interleukin 2 titer 4 hrs after the induction of preincubated lymphocytes with Con A was about 20% of maximal activity. The possible mechanism of early interleukin 2 production is under discussion.