Suppression of mitogen- and tumor-cell-induced lymphocyte stimulation by tumor-associated fetal antigens

The ability of tumor-associated fetal antigens (TAFA) to suppress mitogen and tumor-cell-induced blastogenesis was investigated. Three different TAFA (I, III, and IV) were tested in PHA and Con A lymphocyte proliferation assays. Spleen cells from New Zealand black rats (NBR) were fractionated over nylon wool; and nonadherent (NA) and adherent (AD) cells were compared with unfractionated (UF) cell responses. Preincubation of NA cells with TAFA-I was followed by addition of phytohemagglutinin (PHA) elicited suppression in a 3-to 4-day assay. UF cells were unresponsive to TAFA and/or PHA at all concentrations tested. TAFA dose—response titration curves in Con A proliferation assays revealed that all TAFA tested (TAFA I, -III, and -IV from fibrosarcomas; TAFA-I and -III from osteosarcomas) were suppressive. For some TAFA, nanogram quantities produced significant suppression. In mixed leukocyte tumor cell assays (MLTC) both UF and NA normal rat spleen cells were tested for proliferative responses to syngeneic tumor cells. Four distinct TAFA, purified by high-pressure liquid chromatography, suppressed lymphocyte proliferation when added to MLTC cultures in 5-day assays. Specificity experiments demonstrated that trinitrophenol-bovine serum albumin did not produce similar immunosuppression. TAFA did not block recognition of tumor antigen nor produce nonspecific cytotoxicity of the spleen cells. Significant suppression of DNA synthesis was produced by TAFA-1 following cocultivation with spleen and tumor cells for 1, 2, and 3 days, compared to no suppression when spleen and tumor cells were washed free of TAFA-I prior to tumor cell addition at Day 0. Similar experiments using rat embryo fibroblasts (REF) as stimulators demonstrated that pre-REF cocultivation treatment of lymphocytes with TAFA-I significantly reduced subsequent blastogenic responses. This effect was not reversible; however, if TAFA-I was added to responders previously stimulated by REF, a suppressive response was not seen. Experiments were also carried out to determine the reversibility of TAFA-I effects. Cells were treated with TAFA-I from 1 to 5 days, followed by determination of lymphocyte blastogenesis. TAFA-I effects are reversible and antigen presence is required to completely suppress (or inhibit) stimulation by tumor cells.     

Membrane fluidity of guinea pig lymphocytes and the dysfunction of the respiratory airway and lymphocyte beta-adrenergic systems of the guinea pig

The beta-adrenergic receptor responsiveness of isolated guinea pig tracheal spirals can be negatively affected by intraperitoneal administration of the Gram-negative bacterium Haemophilus influenzae, four days prior to the experiment. The reduction in tracheal relaxation is accompanied by a decrease in beta-adrenergic receptor binding sites in splenic lymphocyte membranes and by a decrease in the fluidity of these membranes. The H. influenzae-induced dysfunction of both the respiratory airway and lymphocyte beta-adrenergic systems can be mimicked by modulating the amount of linoleic acid in the diet. This linoleic acid induced dysfunction of the beta-adrenergic system is also accompanied by a decrease in the plasma membrane fluidity of the splenic lymphocyte membranes of the guinea pigs. The role for plasma membrane fluidity in asthma is discussed in relation to current concepts for atopy.     

The cardiotonic effects of levosimendan in guinea pig hearts are modulated by beta-adrenergic stimulation

The effects of the Ca2+-sensitiser levosimendan alone or in combination with beta-adrenergic stimulation on the contractile function were studied in various guinea pig cardiac preparations. Echocardiography in narcotised animals indicated that a maximal dose of levosimendan (50 microg x kg(-1)) increased the left ventricular posterior wall movement velocity during systoles and diastoles by 25 +/- 3% (mean +/- S.E.M.) and 17 +/- 2%, respectively. In Langendorff hearts, a saturating concentration of levosimendan (0.3 micromol x l(-1) for 5 min) increased +dP/dt(max) and dP/dt(max) by 28 +/- 3% and 14 +/- 2%, respectively. Further, the Ca2+-sensitising potential of levosimendan in Triton-skinned cardiomyocytes (EC50: 5 +/- 3 nmol x l(-1)) was illustrated by a maximal increase in the isometric force production by 51 +/- 5% (at pCa 6.2). However, following stimulation by isoproterenol, when the level of troponin I phosphorylation was elevated, no significant additional increase in the contractile parameters could be demonstrated upon levosimendan administration. Moreover, the levosimendan-induced increase in force production in isolated skinned myocytes could be prevented by incubation with the catalytic subunit of protein kinase A (100 U x ml(-1) for 40 min). These data indicate that thin filament-targeted Ca2+-sensitisation by levosimendan is modulated by phosphorylation of the contractile filaments, an effect that should be considered during combination therapy with levosimendan.