[Preparation and characterization of monoclonal antibodies to the cholera toxin].

Monoclonal antibodies to cholera toxin were obtained. They do not cross-react with the termolabile toxin (LT) of Escherichia coli, ricin, diphtherial toxin, staphylococcus enterotoxins of SEA, SEB, SEI, SEG, or the lethal factor and protective antigen of the anthrax toxin. Pairs of antibodies for the quantitative measurement of the cholera toxin in sandwich enzyme immunoassay (EIA) were selected. The detection limit of the toxin is 0.2 ng/ml for plate EIA and 0.44 ng/ml for microchip EIA. The presence of milk, broth, or surface water in the toxin samples does not reduce the sensitivity of EIA.

Glucosaminylmuramyl dipeptide potentiates the effects of tumor necrosis factor-alpha and cisplatin on transformed cells in vitro.

We studied the effect of combined treatment with cisplatin, glucosaminylmuramyl dipeptide, and TNF-alpha on viability of MCF-7, U-937, B16, and L-929 tumor cells, Ehrlich ascites carcinoma cells, and normal cells (human peripheral blood lymphocytes, peritoneal macrophages, and mouse bone marrow cells). Glucosaminylmuramyl dipeptide was nontoxic for normal and tumor cells, but promoted death of tumor cells after administration in combination with cisplatin and/or TNF-alpha. At the same time, glucosaminylmuramyl dipeptide did not modulate the cytotoxic effect of individual or combined treatment with cisplatin and TNF-alpha on normal cells. Administration of glucosaminylmuramyl dipeptide to cultured MCF-7 cells 20 h before the study increased the potentiating effect of muramyl peptide.

Endogenous tumour necrosis factor-alpha sensitise melanoma cells to glucosaminylmuramyl dipeptide.

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.

Production of interleukin 2 in serum-free medium.

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.

The biochemical study of rat T-cell growth factor (interleukin 2).

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.