Cyclic AMP inhibition of cytotoxin ("lymphotoxin") elaboration by stimulated lymphocytes

Reduced responsiveness of adenylate cyclase to forskolin in human lymphoma cells

The beta 2-adrenergic transmembrane signal transduction was investigated in malignant B-cells from 15 patients with low grade non-Hodgkin's lymphoma as compared with normal lymphocytes of seven healthy adults. The number of beta 2-adrenoceptors and the response of adenylate cyclase (AC) to isoproterenol were slightly decreased in lymphoma cells. The responsiveness of AC to forskolin was 8-fold lower in lymphoma cells, whereas the response to cholera toxin showed no difference. These findings demonstrate an impairment of the beta 2-adrenergic signal transduction in low grade lymphoma cells that particularly affects the function of AC. The comparison with forskolin resistant mutants of an adrenocortical tumor cell line, Y1 (Schimmer et al., J Biol Chem 262: 15521-15526, 1987), suggests that the availability of functional active alpha subunits of stimulatory G proteins (Gs) might be reduced in human B-cell lymphoma, although other mechanisms known to inhibit the AC activity might be involved.

Lymphokine-mediated suppression of chondrocyte glycosaminoglycan and protein synthesis

Spontaneously released and T cell mitogen augmented lymphokine produced by human mononuclear cells has been shown to induce a concentration dependent reversible suppression of chondrocyte glycosaminoglycan and protein synthesis without significantly enhancing chondrocyte catabolic activity. The modulatory factor(s) is of T cell origin and is trypsin, pronase, and heat sensitive. Prostaglandin inhibitors failed to influence factor formation or activity. Although eluting from Sephadex G-100 over a wide range, peak activity had an approximate molecular weight of 53,000 and appeared distinct from recognized forms of lymphotoxin.

Effect of human leucocyte migration inhibitory factor (LIF) on 3', 5'-cyclic AMP levels of peripheral blood leucocytes

The possible involvement of 3', 5'-cyclic AMP (cyclic AMP) in the mechanism of action of leucocyte migration inhbitory factory (LIF) was tested. LIF-treated human peripheral blood leucocytes were incubated at 37 degrees C for various times between 0 and 22 h. The concentrations of cyclic AMP in these cultures did not differ from those in controls. Furthermore, LIF did not affect the cellular release of cyclic AMP. Neither when testing purified neutrophils, which are the prime targets of LIF action, an effect of LIF was found. Cyclic AMP levels decreased with time of incubation, whether testing mononuclear cells (92 per cent lymphocytes), purified neutrophils (98 per cent), or buffy coat cells (72 per cent neutrophils; 22 per cent lymphocytes). However, a transient and as yet unexplained increase in the cyclic AMP levels of the latter mixed population of cells was manifested within 10 to 30 min of incubation.

Immunological investigations of patients with transplanted cornea

Authors examined the role of the cellular immunity by the method (I) of lymphoblastic transformation in 26 keratoplasty cases. Only in one case did they observe significant blast transformation, in this case the keratoplasty was necessary after injury with lime. In the rest of the cases no positive result were ever obtained. They investigated the cellular immunoreactivity of 10 patients waiting for keratoplasty and 10 cataractous patients against cornea antigen by means (II) of the Leucocyte Migration Test (LMT). The change of the cellular immuno-reactivity against cornea antigen was examined on the 1st, 4th, 7th, 14th, 21st, and 28th days after keratoplasty. It could be established that after keratoplasty the LMT became positive (inhibition or stimulation of migration). The results of the LMT investigations obtained on keratoplasty patients by cornea antigen may be of some help for the understanding of the events in the postoperative phase and sometimes also may eventually require immunosuppressive therapy.

Theobromine and theophylline

Theobromine and theophylline have a limited therapeutic use and in addition they occur in plants used in the preparation of a number of widely consumed drinks. Thus most of the population must be exposed to both compounds. Chromosome abnormalities are caused by both theobromine and theophylline in plant cells and in mammalian cells in culture, and both have anti-mitotic activity. While they are fairly potent mutagens in Escherichia coli and other lower organisms the rather scanty available evidence suggests that they are not mutagenic in mammals. The difference in mutagenic activity may be due to the reported inability of E. coli to demethylate these compounds, a process which occurs readily in mammals including man. The structure-activity relationships of these compounds are complex but the available evidence suggests that methylation at position 1 is the most important for both mutagenic activity and the anti-mitotic effect while methylation at position 3 is of most importance in the action on chromosomes.

On the relation of products of activated lymphocytes to cell-mediated cytolysis

Experiments have been designed to test the hypothesis that soluble mediator production and T-cell-mediated cytotoxicity are necessarily related phenomena, and that soluble mediators may be involved in the mechanism of cytolysis. To this end, agents known to inhibit T-cell-mediated lysis in vitro have been studied for their effects on the production of two lymphocyte-derived mediators, lymphotoxin (LT) and migration inhibitory factor (MIF). A clear dissociation between mediator production and cell-mediated cytolysis was found using inhibitors of protein synthesis. Pactamycin and emetine, in doses of 10(-7) M to 10(-6) M, suppressed production of MIF and LT with only slight effect on killing of mastocytoma cells by immune T cells. On the other hand colchicine and vinblastine inhibited T-cell-mediated cytolysis in a dose-related manner but had no significant effect on either MIF or LT production, A striking dichotomy was also observed after augmentation of intracellular cyclic 3'5' adenosine monophosphate (cAMP) levels with cholera enterotoxin. Increased cAMP levels were associated with abrogation of direct lytic activity, but were without significant effect on MIF or LT production in guinea pigs or mice. These findings indicate that mediator production and direct lymphocyte-mediated cytolysis can be experimentally dissociated and represent independent cell-mediated immune functions.