The thyroid status reprograms T cell lymphoma growth and modulates immune cell frequencies

In spite of considerable evidence on the regulation of immunity by thyroid hormones, the impact of the thyroid status in tumor immunity is poorly understood. Here, we evaluated the antitumor immune responses evoked in mice with different thyroid status (euthyroid, hyperthyroid, and hypothyroid) that developed solid tumors or metastases after inoculation of syngeneic T lymphoma cells. Hyperthyroid mice showed increased tumor growth along with increased expression of cell cycle regulators compared to hypothyroid and control tumor-bearing mice. However, hypothyroid mice showed a higher frequency of metastases than the other groups. Hyperthyroid mice bearing tumors displayed a lower number of tumor-infiltrating T lymphocytes, lower percentage of functional IFN-γ-producing CD8(+) T cells, and higher percentage of CD19(+) B cells than euthyroid tumor-bearing mice. However, no differences were found in the distribution of lymphocyte subpopulations in tumor-draining lymph nodes (TDLNs) or spleens among different experimental groups. Interestingly, hypothyroid TDLN showed an increased percentage of regulatory T (Treg) cells, while hyperthyroid mice displayed increased number and activity of splenic NK cells, which frequency declined in spleens from hypothyroid mice. Moreover, a decreased number of splenic myeloid-derived suppressor cells (MDSCs) were found in tumor-bearing hyperthyroid mice as compared to hypothyroid or euthyroid mice. Additionally, hyperthyroid mice showed increased cytotoxic activity, which declined in hypothyroid mice. Thus, low levels of intratumoral cytotoxic activity would favor tumor local growth in hyperthyroid mice, while regional and systemic antitumor response may contribute to tumor dissemination in hypothyroid animals. Our results highlight the importance of monitoring the thyroid status in patients with T cell lymphomas.

KEY MESSAGES

T cell lymphoma phenotype is paradoxically influenced by thyroid status. Hyperthyroidism favors tumor growth and hypothyroidism rises tumor dissemination. Thyroid status affects the distribution of immune cell types in the tumor milieu. Thyroid status also modifies the nature of local and systemic immune responses.

Thyroid status modulates T lymphoma growth via cell cycle regulatory proteins and angiogenesis

We have shown in vitro that thyroid hormones (THs) regulate the balance between proliferation and apoptosis of T lymphoma cells. The effects of THs on tumor development have been studied, but the results are still controversial. Herein, we show the modulatory action of thyroid status on the in vivo growth of T lymphoma cells. For this purpose, euthyroid, hypothyroid, and hyperthyroid mice received inoculations of EL4 cells to allow the development of solid tumors. Tumors in the hyperthyroid animals exhibited a higher growth rate, as evidenced by the early appearance of palpable solid tumors and the increased tumor volume. These results are consistent with the rate of cell division determined by staining tumor cells with carboxyfluorescein succinimidyl ester. Additionally, hyperthyroid mice exhibited reduced survival. Hypothyroid mice did not differ significantly from the euthyroid controls with respect to these parameters. Additionally, only tumors from hyperthyroid animals had increased expression levels of proliferating cell nuclear antigen and active caspase 3. Differential expression of cell cycle regulatory proteins was also observed. The levels of cyclins D1 and D3 were augmented in the tumors of the hyperthyroid animals, whereas the cell cycle inhibitors p16/INK4A (CDKN2A) and p27/Kip1 (CDKN1B) and the tumor suppressor p53 (TRP53) were increased in hypothyroid mice. Intratumoral and peritumoral vasculogenesis was increased only in hyperthyroid mice. Therefore, we propose that the thyroid status modulates the in vivo growth of EL4 T lymphoma through the regulation of cyclin, cyclin-dependent kinase inhibitor, and tumor suppressor gene expression, as well as the stimulation of angiogenesis.

Induction of apoptosis in T lymphoma cells by long-term treatment with thyroxine involves PKCζ nitration by nitric oxide synthase

Thyroid hormones are important regulators of cell physiology, inducing cell proliferation, differentiation or apoptosis, depending on the cell type. Thyroid hormones induce proliferation in short-term T lymphocyte cultures. In this study, we assessed the effect of long-term thyroxine (T4) treatment on the balance of proliferation and apoptosis and the intermediate participants in T lymphoma cells. Treatment with T4 affected this balance from the fifth day of culture, inhibiting proliferation in a time-dependent manner. This effect was associated with apoptosis induction, as characterized through nuclear morphological changes, DNA fragmentation, and Annexin V-FITC/Propidium Iodide co-staining. In addition, increased iNOS gene and protein levels, and enzyme activity were observed. The generation of reactive oxygen species, depolarization of the mitochondrial membrane, and a reduction in glutathione levels were also observed. The imbalance between oxidants and antioxidants species is typically associated with the nitration of proteins, including PKCζ, an isoenzyme essential for lymphoma cell division and survival. Consistently, evidence of PKCζ nitration via proteasome degradation was also observed in this study. Taken together, these results suggest that the long-term culture of T lymphoma cells with T4 induces apoptosis through the increased production of oxidative species resulting from both augmented iNOS activity and the loss of mitochondrial function. These species induce the nitration of proteins involved in cell viability, promoting proteasome degradation. Furthermore, we discuss the impact of these results on the modulation of T lymphoma growth and the thyroid status in vivo.

Possible involvement of stress hormones and hyperglycaemia in chronic mild stress-induced impairment of immune functions in diabetic mice

Stress, an important aspect of modern life, has long been associated with an altered homeostatic state. Little is known about the effect of the life stress on the outcome of diabetes mellitus, especially related to the higher risk of infections. Here, we evaluate the effects of chronic mild stress (CMS) exposure on the evolution of type I diabetes induced by streptozotocin administration in BALB/c mice. Exposure of diabetic mice to CMS resulted in a significant reduction of survival and a sustained increase in blood glucose values. Concerning the immune response, chronic stress had a differential effect in mice with diabetes with respect to controls, showing a marked decrease in both T- and B-cell proliferation. No correlation was found between splenic catecholamine or circulating corticosterone levels and the proliferative response. However, a significant negative correlation was found between glucose levels and concanavalin A- and lipopolysaccharide-stimulated proliferative responses of T and B cells. A positive correlation between blood glucose and splenic catecholamine concentrations was found in diabetic mice but not in controls subjected to CMS. Hence, the present report shows that diabetic mice show a worse performance in immune function after stress exposure, pointing to the importance of considering life stress as a risk factor for patients with diabetes.

Chronic restraint stress impairs T-cell immunity and promotes tumor progression in mice

Long-term exposure to stressful situations can affect the immune system. The T-cell response is an important component of anti-tumoral immunity. Hence, impairment of the immune function induced by a chronic stressor has been postulated to alter the immunosurveillance of tumors, thus leading to a worse neoplastic prognosis. Here, we show that chronic restraint stress affects T-cell mediated immunity in mice. This was evidenced by a decrease of mitogen-induced T-cell proliferation, a reduction in CD4(+)T lymphocyte number and a decrease of tumor necrosis factor-alpha (TNF-alpha) and Interferon-gamma (IFN-gamma) production in stressed mice. Additionally, mice subjected to chronic restraint stress displayed an enhancement of tumor growth in a syngeneic lymphoma model, i.e. an increase of tumor proliferation and a reduction of animal survival. Finally, stressed mice had a reduced specific cytotoxic response against these tumor cells. These results suggest that chronic exposure to stress promotes cancer establishment and subsequent progression, probably by depressing T-cell mediated immunity. The T-cell immunity impairment as well as the tumor progression enhancement emphasize the importance of the therapeutic management of stress to improve the prognosis of cancer patients.

Helicobacter spp. from gastric biopsies of stranded South American fur seals (Arctocephalus australis)

Gastrointestinal lesions with uncertain etiology have been widely described among pinnipeds. The aim of our study was to investigate the presence of Helicobacter spp. in the gastric mucosa of South American fur seals (Arctocephalusaustralis). Gastric biopsies from thirteen seals, stranded on the shores of the Southwestern Atlantic Ocean in Argentina, were evaluated for the presence of Helicobacter spp. by PCR and DNA sequence analysis. Six gastric biopsies were positive for Helicobacter spp. Pairwise sequence comparisons showed less than 95% identity to novel Helicobacter spp. described from pinnipeds from North America and Australia. However, phylogenetic analysis revealed that the South American fur seal sequences clustered with 99-100% homology with H. cetorum, a species isolated from dolphins and whales. The presence of H. cetorum in pinnipeds, if confirmed by its isolation from the gastric mucosa of these mammals, demonstrates the wide host range of this bacterium in the marine environment.

Protein kinase C-dependent NF-kappaB activation is altered in T cells by chronic stress

Chronic stress has been associated with impaired immune function. In this work we studied the effect of chronic mild stress (CMS) exposure on the early intracellular pathways involved in T cells after stimulation with mitogen. We found that mitogen stimulation of T lymphocytes from CMS-exposed mice resulted in a reduction of the intracellular [Ca2+] rise, an impairment of growth-promoting protein kinase C (PKC) activation, a lower NF-kappaB activation and an increase in the inhibitory cAMP-protein kinase A (PKA) pathway activity with respect to those found in control lymphocytes. However, T cell activation with the direct PKC activator phorbol 12-myristate 13-acetate plus calcium ionophore led to a similar proliferative response in both CMS and control lymphocytes, indicating that signals downstream of PKC would not be affected by stress. In summary, our results show that chronic stress induced an alteration in T cell early transduction signals that result in an impairment of the proliferative response.

In vivo iron and zinc deficiency diminished T- and B-selective mitogen stimulation of murine lymphoid cells through protein kinase C-mediated mechanism

Zinc and iron are crucial mineral components of human diet, because their deficiency leads to several disorders, including alterations of the immune function. It has been demonstrated, in both humans and rodents, that a diminished number of lymphoid cells and a loss of lymphocyte activity accompany deprivation of these essential minerals. The aim of this work was to analyze if iron and/or zinc imbalances regulate lymphocyte activity and the intracellular signals involved in the effect. Mice from the BALB/c strain were fed with iron- and/or zinc-deficient or mineral-supplemented diets, according to the American Institute of Nutrition Rodent Diets. Levels of iron and zinc were assessed in blood, liver, or bone samples. Selective mitogen stimulation of T- and B-lymphocytes were performed. We found a diminished proliferative response in T- and B-lymphocytes from zinc- and/or iron-deficient animals with respect to controls. These effects were related to decreased mitogen-induced translocation of protein kinase C (PKC) activity to cell membranes on both cell types from all animals fed with deficient diets. Our results demonstrate that iron and zinc deficiencies affect both T- and B-lymphocyte function by PKC-dependent mechanisms.

Chronic stress influences the immune system through the thyroid axis

The aim of the present work was to analyze the effect of chronic stress on thyroid axis and its influence on the immune response. For this purpose a murine model of chronic stress was developed to evaluate and to correlate thyroid hormone levels with humoral alloimmune response. Results show a reduction in serum levels of thyroid hormones, specially a significant decrease in serum levels of triiodotyronine (T3) in stressed animals. On the other hand, alloimmunization was not able to induce an early increment in T3 and thyroxine (T4) levels as it was previously reported in normal animals. In addition, lower titers of alloantibodies were obtained in animals under stress conditions as compared to normal mice. The sustitutive T4 treatment in stressed animals increased significantly alloantibody production as well as the early increment in thyroid hormones after antigenic challenge. These findings suggest that chronic stress induces an alteration of the function of thyroid axis that alters the immune response.

Altered beta-adrenoceptor function associated to protein kinase C activation in hyperproliferative T lymphocytes

beta-Adrenoceptor (betaAR) expression and function as well as its modulation via intracellular transduction signals, were analyzed on the T cell lymphoma BW5147. Independently to the kinetic of proliferation and relative to the number of receptors displayed in normal T lymphocytes, BW5147 cells displayed a decreased number of betaAR, uncoupled to adenylate cyclase, but coupled to protein kinase C stimulation. This last effect was impaired by a beta-antagonist and by blockers of the enzymatic pathways involved in T lymphocyte proliferation, inducing a recovery of betaAR sites. Down-regulation of betaAR would implicate the loss of a negative neuroimmune control mechanism for lymphocyte proliferation. The coupling of the remaining sites to a positive signal for cellular activation, would contribute to establish an hyperproliferative state.

Experimental evidence pointing to the bidirectional interaction between the immune system and the thyroid axis

Among the many examples of neuroendocrine-immune system interactions the relationship between the thyroid axis and the immune function has yet to be clearly established. Here we studied the influence of thyroid hormones on the course of an alloimmune response. Murine T(3) and T(4) levels were found to be increased a few days after the immunization of mice with allogeneic lymphoid cells. Besides in vivo treatment with T(4) was shown to increase alloantibody titers during the early stages of alloimmunization and to enforce lymphoid proliferation in vitro in a mixed lymphocyte reaction. Conversely, lowering thyroid hormone seric levels by propylthiouracil treatment, negatively modulates the humoral and cellular alloimmune responses. The evidence here points to the existence of a bidirectional communication between both systems. The possibility that the antigenic challenge would increase the thyroid gland activity thus leading to a positive modulatory action upon the immune response is also discussed.

Downregulation of beta adrenergic receptor expression on B cells by activation of early signals in alloantigen-induced immune response

Previously we described a decrease in beta-adrenergic receptor expression in B lymphocytes as a consequence of in vivo alloimmunization. This decrease correlates with the highest response of alloantibody production by B cells. In the present report we examined the participation of intracellular signals elicited after alloimmune stimulation. We showed that in vitro stimulation of B cells with mitomycin C-treated allogenic cells induced a reduction in the number of beta-adrenoceptors. This downregulation correlated to changes in basal and in isoproterenol-stimulated intracellular cAMP levels. We found that calcium mobilization and protein kinase C activation triggered after direct allogenic stimulation and/or by the action of T cell-soluble factors induced the reduction in beta-adrenoceptor sites. These findings could be of interest to understand the neuroendocrine mechanisms involved in the regulation of B cell activation.

Role of protein kinase C and cAMP in fluoxetine effects on human T-cell proliferation

In this work, we studied the effect of fluoxetine on human T-lymphocyte proliferation using optimal and suboptimal concanavalin A concentrations. In particular, we analyzed the influence of fluoxetine on the kinases that are involved in intracellular signalling after stimulation with mitogens. We found that fluoxetine promoted the Ca2+ -mediated proteolysis of protein kinase C (PKC) and increased cyclic-AMP (cAMP) levels, thereby impairing lymphocyte proliferation, when optimal concanavalin A concentrations were used. In contrast, when suboptimal concanavalin A concentrations were used, fluoxetine only increased PKC translocation, without modifying cAMP levels, leading to T-cell proliferation. According to our results, fluoxetine has a dual effect on T-cell proliferation by modulating the PKC and protein kinase A pathways. This mechanism is thought to be mediated through Ca2+ mobilization.

Fluoxetine action upon human T lymphocyte proliferation

The purpose of this study was to analyze the effect of fluoxetine upon human T lymphocyte proliferation, and to assess the early signals elicited after T cell triggering and cAMP formation. Blood samples from normal human volunteers were drawn from venipuncture and T cells were cultured in the presence or absence of Concanavalin A (Con A) and fluoxetine. Protein Kinase C (PKC) levels and cyclic adenosine monophosphate (cAMP) formation were also measured. Fluoxetine exerted dual effect, depending on the degree of lymphocyte activation: at mitogenic concentrations of Con A (2 micrograms/ml), we observed an inhibitory effect on cellular proliferation. This inhibitory effect involves PKC degradation and cAMP formation. On the other hand, when submitogenic Con A concentrations (1 microgram/ml) were used, fluoxetine stimulated the cellular response and increased PKC translocation. The participation of extracellular calcium mobilization could be involved in these mechanisms. According to our results, fluoxetine seems to modulate calcium influx which, in turn, would influence PKC translocation, thus modulating the immune response through a mechanism that could be involving cAMP participation.

Down-regulation of beta-adrenergic receptors induced by mitogen activation of intracellular signaling events in lymphocytes

The expression of beta-adrenergic receptors on murine lymphocytes stimulated with concanavalin A was studied. A decrease in beta-adrenoceptor number on T lymphocytes and a diminished response to specific agonist stimulation at the peak of proliferation was found. The blockade of cell proliferation by tyrosine kinases or protein kinase C inhibitors reversed the decrease in beta-adrenoceptor number. PMA plus ionophore or interleukin-2 but not PMA alone were able to induce beta-adrenoceptor down-regulation accompanying cellular proliferation. These results showed that the intracellular signals triggered during lymphocyte activation are involved in beta-adrenoceptor down-regulation and it would represent the loss of a mechanism that exerts negative neuroimmune control of cellular proliferation.

Reduced number and coupling of beta-adrenergic receptors in a modified S49 mouse lymphoma cell line

Long-term culture of S49 wild-type cells in medium containing a high concentration of fetal calf serum leads to a modified (S49m) cell line with a reduced number of beta-adrenergic receptors (R). These S49m cells with a higher rate of proliferation were unable to respond to the beta-adrenergic agonists isoproterenol (ISO) and epinephrine as analysed by measuring adenylate cyclase (ac) activity on purified membranes of these cells. Additionally, no accumulation of cyclic AMP was obtained on S49m intact cells upon stimulation with beta-agonists. Nevertheless, S49m cells were able to respond significantly to the direct activation of the stimulatory guanine nucleotide binding (Gs) protein by aluminium tetrafluoride and sodium fluoride, and to the stimulation of another receptor coupled to the ac system through a Gs protein, by prostaglandin E1 (PGE1). When cloning S49m cells, similar results were obtained upon stimulation with ISO and PGE1 and the cloned cells express the same thy 1.2 and class Id molecules as do S49 cells. The study of S49m cells indicates that they are a beta-adrenergic R-deficient variant distinct from the other variants described for S49 cells.

Increased proliferative activity, loss of beta-adrenergic receptor function and class I major histocompatibility complex antigen surface expression in a modified lymphoma cell line

The molecular interaction of class I major histocompatibility complex (MHC) antigens (Ag) and of beta-adrenergic receptors was previously demonstrated on lymphocytes. By long-term culturing with high concentration of foetal calf serum, the murine S49 lymphoma cell line was modified (S49m) giving phenotypic alterations in beta-adrenergic receptors and class I Ag expression. S49m cells displayed a reduced number of beta-adrenergic sites that were uncoupled to the adenylate cyclase system. These were unable to respond to beta agonist stimulation, despite the fact that direct activation of Gs could be achieved with aluminium tetrafluoride. Although S49m cells showed normal expression of the thy 1.2 Ag, they displayed no expression of class I Ag of the d haplotype. This was assessed by the evident lack of cytotoxic activity of specific monoclonal antibodies (Mo Ab) and of their binding. When performing IFI staining on permeabilized cells, we found positive staining with anti-class d Ab inside the cell. This loss of expression and activity of beta-adrenoceptors and the internalization of class I Ag were accompanied by a higher rate of proliferation in S49m cells. The possibility that the loss of both molecules would modify the biology of the cell is also discussed.

MHC class I-hormone receptor associations: still a physiological enigma?

Besides the important role of the Major Histocompatibility Complex (MHC) class I molecules n physiologically restricting immune responses, they seem to play a non-immunological function by the molecular association with several hormone receptors (R). Among the hormone R and class I antigen (Ag) interactions, insulin R, epidermal growth factor (EGF) R, interleukin-2 (IL-2) R, luteinizing (LH) hormone R, beta adrenergic R and muscarinic cholinergic R were described in several human and animal models. Evidences from immunoprecipitation assays, binding assays and immunofluorescence techniques pointed to the molecular association of all of these R with class I molecules on cellular surfaces. Only for beta adrenergic R, muscarinic cholinergic R and LH-R, antibodies directed against class I products were described to exert the activation of these R leading to the production of intracellular second messengers and consequently modifying the physiology of the corresponding cell. This was also obtained on insulin R with peptides derived from class I molecules. The selectivity or R involved in all studied cellular types, should find its explanation in the physiological importance of the considered R for the indicated cell. The participation of cytoskeletal proteins on these interactions and the proximity on cell surfaces between both molecules, probably managed by ligand-mediated microaggregation, are also facts to be taken into account to better understand the biological consequences of these interactions.

Muscarinic cholinergic receptors on murine lymphocyte subpopulations. Selective interactions with second messenger response system upon pharmacological stimulation

In this study the muscarinic cholinergic receptor capacity and affinity in murine lymphocyte sets and subsets and the biochemical responses obtained by the pharmacological stimulation of cholinergic receptors in these cells was determined by means of binding studies. Saturation assays with the specific radioligand for muscarinic cholinergic receptors ([3H]QNB) showed that B lymphocytes lack high affinity muscarinic cholinergic receptors, while the binding on T cells was a specific and saturable process. Lyt 2.2+ cells have a significantly higher number of receptors (Bmax) than L3T4+ cells; but the equilibrium dissociation constant (Kd) values obtained in both subpopulations did not differ significantly from one another, and resembled the Kd value of T lymphocyte populations. The specific receptor stimulation by carbachol caused a different intracellular signal transduction according the tested cell subtypes. The muscarinic cholinergic stimulation result in a significant inhibition of isoproterenol-stimulated adenylate cyclase system in T, L3T4+ and Lyt 2.2+ cells. On the contrary, Lyt 2.2+ cells were only able to respond to carbachol stimulus increasing cGMP levels and inositol phosphate formation while L3T4+ cells were unable to do it. Results show differences in the expression and in the ability of cholinergic receptors in sets and subsets of murine lymphocytes to trigger intracellular second-messenger systems. The differential receptor expression and the second-messenger response systems could be important to study the modulation of cellular immune response by cholinergic stimulation.

Beta-adrenoceptor distribution in murine lymphoid cell lines

beta-Adrenergic receptors (R) on several tumor lymphoid cell lines were characterized both directly by beta radioligand binding of 125iodo-cyanopindolol (125I-CYP) to intact cells and membranes, and functionally by assessing hormone-dependent changes in cyclic 3',5' adenosine monophosphate (cAMP) levels on intact cells and measuring adenylate cyclase (a.c.) activity on membranes. Only two lymphoid cell types, BW 5147 (a T cell derived lymphoma cell line) and TIB 221 (a B cell derived line) displayed significant amounts of beta-adrenergic R by 125I-CYP specific binding. Despite this, no stimulation of the a.c. activity was found in the presence of beta-adrenergic agonists in these cells in comparison with native lymphocytes or cells of the well-known S49 cell line used as a positive control. beta-Adrenoceptor specific uncoupling was confirmed by aluminum tetrafluoride (AlFl4) direct activation of the a.c. system in the beta R-bearing cell membranes and by an increase in cAMP production induced by PGE1, another hormone that activates the a.c. Structural characterization of beta-adrenoceptors by photoaffinity-labeling demonstrates that uncoupling was not due to a structural alteration of the beta-adrenergic R expressed in these lymphoma cell lines, as these R gave similar results as native or S49 cells. It can be concluded that functional beta-adrenoceptors are absent in these lymphoma cells. The possible implication of alternative transmission pathways and original neuroendocrine control in tumor lymphoid cells is discussed.

Allogenic stimulus induces prostaglandin and thromboxane production in T lymphocytes

We have examined the influence of an allogeneic stimulus on T lymphocyte prostanoid synthesis. PGE2 and TXB2 (the stable product of TXA2) were determined by radioimmunoassay. When T cells were derived from alloimmunized animals, the production of PGE2 and TXA2 was significantly higher than that of non-immunized cells. Moreover, T immune lymphocytes in the presence of the immunized alloantigen showed an increment in prostanoid production. We propose that the allogeneic stimulus provides a signal to the T lymphocytes for an increase in prostanoid synthesis.

Stimulation of phosphoinositide hydrolysis via class I antigen-specific recognition in murine cardiac tissue

Induction of polyphosphoinositide hydrolysis in cardiac tissue by specific recognition of class I histocompatibility antigens was assayed. C3H (H-2k) mice auricles were labelled with myo-[3H]inositol precursor and inositol phosphate production in the presence or absence of anti-class I k products was measured. Anti-class I, but not anti-class II products specifically increased phosphoinositide turnover. This increment was partially blocked by muscarinic cholinergic and alpha-adrenergic blockers and even more so by the phospholipase C inhibitor NCDC. Alloantibodies specifically directed against class I antigens could then exert stimulation of phospholipase C-mediated phosphoinositide hydrolysis through the interaction with muscarinic cholinergic and/or alpha-adrenergic receptors. The induction of intracellular second messengers by class I antigens and hormone-receptor interactions is discussed.

Biological effects and cyclic AMP production during molecular histocompatibility antigen and beta-adrenoceptor interactions

It has been previously demonstrated that murine alloimmune IgG, while specifically recognizing class I histocompatibility (HC) antigens (Ag) of cardiac tissue, was able to increase the contractile tension and frequency of spontaneously beating isolated preparations and that this effect involved beta adrenoceptor activation. Here we show that beta 1 adrenoceptors of murine myocardium are the only stimulatory cardiac receptors that could interact with alloantibodies (allo-Ab), as the specific blockade of stimulant receptors did not alter alloimmune IgG mechanical effect on atria. Moreover, beta adrenergic participation in the phenomenon was confirmed by the isoproterenol-like increase of cardiac cAMP levels in cardiac preparations pre-treated with allo-Ab, that could be blocked by the beta antagonist propranolol. We also show that alloimmune IgG fixation to myocardium could be specifically interfered with by beta- and beta 1-selective blockers. All these data point to the fact that the mechanism whereby alloimmune IgG may trigger a beta adrenergic biological effect is through a direct molecular interaction between HC Ag and adenylate cyclase-coupled beta adrenoceptors.

H-2 specific inotropic effect of alloimmune lymphoid cells on mouse isolated atria

Alloimmunized lymphoid cells exert inotropic effects on isolated mouse atria. We here show that, when thymocytes were assayed on spontaneously beating isolated atria, a negative inotropic effect always appeared. When lymph node or spleen cells were assayed, they led to a biphasic effect: negative or positive inotropic effect, depending on the number of immunizations. Non-immunized lymphoid cells never exerted inotropic effects. Supernatants of alloimmunized cells cocultivated with pieces of atria from the immunizing strain exerted pharmacological effects on atria that mimicked those of whole cells. Inhibitors of lipoxygenase(s) and cyclooxygenase of arachidonic acid metabolism, inhibited the positive and negative inotropic effects, respectively. The specificity of the negative and positive inotropic effects, both in their induction and expression, was linked to the major histocompatibility complex. When T and B cells were purified from lymphoid tissues we found that they were responsible for the negative and positive inotropic effects on atria, respectively. Additionally, supernatants of T cells cultured with alloextracts triggered negative inotropic effects, but those from B cells were inactivated.

Pharmacologic effects on mouse isolated atria of immunoglobulins directed against class I histocompatibility antigens

Sera from alloimmunized mice exert potent inotropic and chronotropic effects on mouse isolated atria. In this report, we present data showing that both total immunoglobulins and purified IgG from alloimmunized mice were able to exert per se these effects. The pharmacologic effects of IgG were parallel to its cytotoxic titer but not to its immunofluorescence titer. The specificity of the inotropic and chronotropic effects was studied by using several interstrain immunizations and target atria. It was observed that only the sera from mice immunized with H-2-disparate cells were able to exert pharmacologic effects on atria; these effects were evident not only on atria from the immunizing strain, but also on atria from other strains having identical H-2 but different backgrounds. Neither normal sera nor sera from animals immunized against non-H-2 differences were active. The effect of sera, total immunoglobulins, and purified IgG were blocked by propranolol, suggesting the involvement of beta-adrenoreceptor in the reaction.

Pharmacologic effects on mouse isolated atria of immunoglobulins directed against class I histocompatibility antigens

Sera from alloimmunized mice exert potent inotropic and chronotropic effects on mouse isolated atria. In this report, we present data showing that both total immunoglobulins and purified IgG from alloimmunized mice were able to exert per se these effects. The pharmacologic effects of IgG were parallel to its cytotoxic titer but not to its immunofluorescence titer. The specificity of the inotropic and chronotropic effects was studied by using several interstrain immunizations and target atria. It was observed that only the sera from mice immunized with H-2-disparate cells were able to exert pharmacologic effects on atria; these effects were evident not only on atria from the immunizing strain, but also on atria from other strains having identical H-2 but different backgrounds. Neither normal sera nor sera from animals immunized against non-H-2 differences were active. The effect of sera, total immunoglobulins, and purified IgG were blocked by propranolol, suggesting the involvement of beta-adrenoreceptor in the reaction.

Beta-adrenergic inhibitory effect of alloimmune antibody on isolated oviductal tract of mice

The effects of IgG purified from BALB/c anti CF1 sera on the spontaneous contractions of isolated oviductal tract from CF1 mice were explored. Cumulative dose-response curves were constructed for the effect of immune IgG on nice oviductal tracts from proestrus, estrus, metestrus and diestrus, comparing them with those obtained with norepinephrine. Both the adrenergic agonist and the immune IgG produced a sustained inhibition of spontaneous motility during the whole sex cycle. Normal IgG was virtually devoid of activity. The sensitivity of CF1 mouse oviducts to the inhibitory actions of immune IgG and norepinephrine varied depending on the hormonal stage, i.e. it was higher in natural diestrus than in metestrus; it became smaller in proestrus and was minimal during estrus. The mechanism triggered involved a beta-adrenergic reaction that could be blocked by 10(-7) M (-)-propranolol and 10(-6) M butoxamine and potentiated by chemical sympathectomy of the mice with 6-hydroxydopamine. It is concluded that: (a) alloimmune antibody reacts with isolated oviductal tract of mice inducing functional changes; (b) this action could be associated with an activation of postsynaptic beta-adrenergic sites of the plasma membrane and (c) the different effectiveness of the immune IgG observed during the sex cycle appears to depend on the affinity of beta-adrenoreceptors to react with it.

Effect of alloimmunized thymic cells on isolated mouse atria. Participation of prostaglandins

The effects of thymic cells from alloimmunized mice on the mechanical activity of isolated mouse atria were explored. Immune cells decreased the tension without changing the rate of beating of the atrium. After inhibition of prostaglandin synthesis with indomethacin and acetylsalicylic acid, the negative inotropic action of alloimmunized thymic cells was blocked.

Positive inotropic and chronotropic effect of alloimmune sera on isolated mouse atria

The effects of alloimmune sera on the contractile tension and frequency of spontaneously beating isolated mouse atria were explored. Immune sera enhanced frequency as well as tension; both effects were blocked by the presence of propranolol. In contrast, pretreatment with 6-OH dopamine potentiated the stimulatory action of immune sera.