Mitogen responsiveness of various immune tissues: heterogeneity of accessory cells and susceptibility to suppression by macrophages

Arachidonic acid in health and disease with focus on hypertension and diabetes mellitus: A review

Arachidonic acid (AA 20:4n-6) is an essential component of cell membranes and modulates cell membrane fluidity. AA is metabolized by cyclo-oxygenase (COX), lipoxygenase (LOX) and cytochrome P450 enzymes to form several metabolites that have important biological actions. Of all the actions, role of AA in the regulation of blood pressure and its ability to prevent both type 1 and type 2 diabetes mellitus seems to be interesting. Studies showed that AA and its metabolites especially, lipoxin A4 (LXA4) and epoxyeicosatrienoic acids (EETs), potent anti-inflammatory metabolites, have a crucial role in the pathobiology of hypertension and diabetes mellitus. AA, LXA4 and EETs regulate smooth muscle function and proliferation, voltage gated ion channels, cell membrane fluidity, membrane receptors, G-coupled receptors, PPARs, free radical generation, nitric oxide formation, inflammation, and immune responses that, in turn, participate in the regulation blood pressure and pathogenesis of diabetes mellitus. In this review, role of AA and its metabolites LXA4 and EETs in the pathobiology of hypertension, pre-eclampsia and diabetes mellitus are discussed. Based on several lines of evidences, it is proposed that a combination of aspirin and AA could be of benefit in the prevention and management of hypertension, pre-eclampsia and diabetes mellitus.

Is There a Role for Bioactive Lipids in the Pathobiology of Diabetes Mellitus?

Inflammation, decreased levels of circulating endothelial nitric oxide (eNO) and brain-derived neurotrophic factor (BDNF), altered activity of hypothalamic neurotransmitters (including serotonin and vagal tone) and gut hormones, increased concentrations of free radicals, and imbalance in the levels of bioactive lipids and their pro- and anti-inflammatory metabolites have been suggested to play a role in diabetes mellitus (DM). Type 1 diabetes mellitus (type 1 DM) is due to autoimmune destruction of pancreatic β cells because of enhanced production of IL-6 and tumor necrosis factor-α (TNF-α) and other pro-inflammatory cytokines released by immunocytes infiltrating the pancreas in response to unknown exogenous and endogenous toxin(s). On the other hand, type 2 DM is due to increased peripheral insulin resistance secondary to enhanced production of IL-6 and TNF-α in response to high-fat and/or calorie-rich diet (rich in saturated and trans fats). Type 2 DM is also associated with significant alterations in the production and action of hypothalamic neurotransmitters, eNO, BDNF, free radicals, gut hormones, and vagus nerve activity. Thus, type 1 DM is because of excess production of pro-inflammatory cytokines close to β cells, whereas type 2 DM is due to excess of pro-inflammatory cytokines in the systemic circulation. Hence, methods designed to suppress excess production of pro-inflammatory cytokines may form a new approach to prevent both type 1 and type 2 DM. Roux-en-Y gastric bypass and similar surgeries ameliorate type 2 DM, partly by restoring to normal: gut hormones, hypothalamic neurotransmitters, eNO, vagal activity, gut microbiota, bioactive lipids, BDNF production in the gut and hypothalamus, concentrations of cytokines and free radicals that results in resetting glucose-stimulated insulin production by pancreatic β cells. Our recent studies suggested that bioactive lipids, such as arachidonic acid, eicosapentaneoic acid, and docosahexaenoic acid (which are unsaturated fatty acids) and their anti-inflammatory metabolites: lipoxin A4, resolvins, protectins, and maresins, may have antidiabetic actions. These bioactive lipids have anti-inflammatory actions, enhance eNO, BDNF production, restore hypothalamic dysfunction, enhance vagal tone, modulate production and action of ghrelin, leptin and adiponectin, and influence gut microbiota that may explain their antidiabetic action. These pieces of evidence suggest that methods designed to selectively deliver bioactive lipids to pancreatic β cells, gut, liver, and muscle may prevent type 1 and type 2 DM.

Inhibition of autoimmune diabetes in NOD mice with serum from streptococcal preparation (OK-432)-injected mice

We have recently reported that systemic and chronic administration of recombinant tumour necrosis factor alpha (TNF-alpha), as well as streptococcal preparation (OK-432), inhibits development of insulin-dependent diabetes mellitus (IDDM) in NOD mice and BB rats, models of IDDM. In this study we examined whether serum containing endogenous TNF induced by OK-432 injection could inhibit IDDM in NOD mice. Treatment twice a week from 4 weeks of age with OK-432-injected mouse serum, which contained endogenous TNF (75U), but not IL-1, IL-2 and interferon-gamma (IFN-gamma) activity, reduced the intensity of insulitis and significantly inhibited the cumulative incidence of diabetes by 28 weeks of age in NOD mice, as compared with the incidence in non-treated mice (P less than 0.01) and in mice treated with control serum (P less than 0.02). This inhibitory effect of the serum was diminished, although not significantly, by neutralization of serum TNF activity with anti-mouse TNF antibody. In the mice treated with the serum from OK-432-injected mice, Thy-1.2+ or CD8+ spleen cells decreased (P less than 0.01) and surface-Ig+ (S-Ig+) cells increased (P less than 0.05), whereas the proliferative response of spleen cells to concanavalin A (P less than 0.01) and lipopolysaccharide (P less than 0.05) increased. The results indicate that the inhibition by OK-432 treatment of IDDM in NOD mice was partially mediated by serum factors including endogenous TNF.

Differentiation of human in vivo antigen-induced lymphoblastoid B cell precursors can be prevented by natural killer cells

Tetanus toxoid (tet) immunization of normal humans leads to the transient appearance in the circulation of large lymphoblastoid (LB) B cells, which spontaneously secrete IgG-tet in short-term cultures. The present work examines the effect of endogenous natural killer (NK) cells, as defined as CD 16+ cells, on the LB B cell subset. NK cell depletion by monoclonal antibody (Leu11) and complement (C)-mediated lysis from LB B cell containing populations eliminated 76 +/- 7% of the cytotoxic activity against 51Cr-K-562 cells, and, in contrast, enhanced 2.7 +/- 0.3 times IgG-tet secretion. Cells untreated, treated with Leu11 alone, C alone, or with an irrelevant monoclonal antibody and C were used as controls. Furthermore, the increased IgG-tet production after NK depletion could be reversed by adding autologous CD 16(+)-enriched populations. Limiting dilution analysis revealed that the NK removal enhancement of IgG-tet production was due to an augmentation (3.18 +/- 0.63 times) of the precursor frequency of spontaneous antibody-secreting cells in NK-depleted cells with respect to control populations. Finally, the spontaneous IgG-tet-producing cells present in NK-depleted and control populations were the same since they produced similar quantities of antibody on a per cell basis and exhibited identical large size, as determined by 1 x G sedimentation technique. NK cells, therefore, exert a strong inhibitory effect on LB B cells by preventing the development of a considerable part of their precursors. This mechanism might be of importance in the control of LB B cells in vivo.

Modified lymphocyte response to mitogens after intraperitoneal injection of glycopeptidolipid antigens from Mycobacterium avium complex

Intraperitoneal injection of glycopeptidolipid (GPL) antigens from Mycobacterium avium complex serovar 4 resulted in the decreased ability of murine splenic lymphocytes to respond to nonspecific-mitogen-induced blastogenesis when exposed to concanavalin A, phytohemagglutinin, and lipopolysaccharide. Adherent cell depletion and cell mixing experiments with T lymphocytes indicated that macrophages were not a major contributor to the immunosuppression observed in this study. Enumeration of splenic lymphocytes by means of flow-cytometry with fluorescein isothiocyanate-conjugated monoclonal antibodies demonstrated that intraperitoneal injection of GPL antigens resulted in a significant decrease in Thy-1+ and Lyt-1+ cells but no change in the numbers of Lyt-2+ cells. Treatment with GPL antigens in vitro affected the ability of splenic mononuclear cells to respond optimally for concanavalin A-induced blastogenesis at 40 micrograms of GPL per 4 X 10(5) cells per 0.2 ml and lipopolysaccharide-induced blastogenesis at concentrations ranging from 5 to 40 micrograms of GPL per 4 X 10(5) cells per 0.2 ml. However, in vitro treatment with GPL antigens did not affect phytohemagglutinin-induced blastogenesis at concentrations ranging from 5 to 40 micrograms of GPL per 4 X 10(5) cells per 0.2 ml. These findings suggest that GPL antigens or their metabolites affect lymphocyte function and may be important cofactors in the overall pathogenesis of M. avium complex infections.

Analysis of the activation of lymphoid cells by mitogens in vitro with limiting dilution methods: adherent peritoneal cells suppress B-cell activation and synergize with WEHI-3 in the activation of T cells by Con A

Adherent peritoneal cells (APC) have often been used as a pure and effective macrophage population. Using partition analysis and small numbers of lymphoid cells activated by mitogens (concanavalin A for T cells (in the presence of TCGF) and LPS + DxS for B cells) we found that APC were accessory cells for T cell activation and growth but were not effective for B cells. Although APC were effective in assisting T-cell mitogenesis, they were not especially efficient. However, when APC were mixed with irradiated WEHI-3 cells (a tissue culture line previously shown to exhibit accessory cell activity in vitro for mitogenic activation T and B cells), the APC and WEHI-3 showed apparent synergy. One reason for failure of APC to assist B-cell mitogenesis was traced to the presence of a suppressor cell population which overcame the accessory cell help given by irradiated WEHI-3 cells to LPS-DxS stimulated murine B cells. It is thus possible to find "helper" effects (synergy of APC and WEHI-3 assisting the mitogenesis of T cells), as well as suppressor effects within the range of cells found in adherent accessory cells.

Macrophages as regulatory cells in mitogen induced spleen cell proliferation. 1. Macrophages as suppressor cells

In this study the effect of alveolar (AC) or peritoneal (PC) lavage cells from Lewis rats on the mitogen induced proliferation of syngeneic spleen cells was investigated. When total spleen cells were stimulated with PHA (5 micrograms/ml) or ConA (6 micrograms/ml), the addition of AC or PC and of their adherent (A) or non-adherent (NA) fractions had dose dependent suppressive effects. After passing the spleen cells through a Sephadex G-10 column, the eluted cells responded poorly to the mitogens. Addition of low numbers (2 X 10(3) = 1%) AC or NA-AC improved this response, whereas higher concentrations (5 or 10%) of these cells or any concentration of A-AC, PC, A-PC or NA-PC showed either none or a suppressive effect. The cells which strongly suppress mitogen induced lymphocyte proliferation have macrophage morphology, are adherent, esterase positive, bear Fc receptor for IgG and bind ganglioside coated erythrocytes. NA-AC were further separated into Ia-depleted (Ia-) and Ia-enriched (Ia+) population. The Ia+ fraction contained 80 to 90% Ia bearing cells, supported the mitogen induced stimulation of Sephadex G-10 depleted spleen cells and was ineffective in suppression. Interestingly, these cells did not bind ganglioside treated sheep erythrocytes. On the other hand, the Ia-negative NA-AC fraction and particularly the A-AC population strongly expressed the "ganglioside receptor" as well as typical macrophage markers like Fc receptors, latex-phagocytosis and non-specific esterase. Therefore, the "ganglioside receptor" may be a useful marker to define suppressor macrophages.

Changes in NK cell activity during the estrous cycle and pregnancy in mice

Changes in NK cell activity during the estrous cycle and pregnancy in mice were studied by a 4 h 51Cr-release assay using YAC-1 cells as a target. NK activity both in the spleen and peripheral blood mononuclear cells showed a single fluctuation with a peak at met-estrous-2 during the estrous cycle. Splenic NK activity was suppressed in the early to mid-stages of pregnancy but increased sharply in the late stage. The activity declined thereafter, reaching the estrous level post-partum. NK activity in the peripheral blood showed a decrease throughout the entire pregnancy, but increased on Day 1 post-partum, returning to the estrous level thereafter. To elucidate the mechanisms involved in these variations of NK activity, NK-enriched and non-adherent cells were prepared from the spleens of mice at estrous and met-estrous-2 and those at early and late stages of pregnancy and then examined for NK activity. The results showed that there was no difference in the cytotoxic activity among these purified NK cells. Adherent cells purified from the spleens of mice in the early stage of pregnancy when co-cultured with the non-adherent NK cell fractions suppressed the NK cytotoxicity. These results strongly suggest the possibility that phagocytic and/or adherent cells may be involved in the regulation of splenic NK activity during the estrous cycle and pregnancy.

Comparative analysis of the immunopharmacological properties of three new nitrosourea analogues: RPCNU, RFCNU and Chlorozotocin

Three sugar derivatives of chloroethyl nitrosoureas: RPCNU, RFCNU and Chlorozotocin (CLZ) were examined for their effect on the immune system in mice when administered at the minimal antineoplastic therapeutic dose. When the drugs were administered 4 days prior to antigenic stimulation, a potentiation of DTH to oxazolone was observed whereas the antibody response to SRBC was markedly decreased. When injected 24 h after immunization, the nitrosourea analogues did not modify the intensity of DTH reaction and of allograft rejection and only RFCNU depressed the antibody response. The proliferative response of spleen cells to T or B cell mitogens was strongly depressed after in vivo treatment with either of the three analogues. Concomitantly, peritoneal macrophages became strongly cytostatic for tumor cells and also displayed an enhanced chemiluminescence upon phagocytosis. An augmentation of antibody-dependent cellular cytotoxicity of spleen cells was observed only after CLZ administration which also resulted in an increase of NK activity of peritoneal cells but in an inhibition of spleen cell cytotoxicity. This study demonstrates that the nitrosourea analogues act as immunomodulating agents and reinforces their interest as antineoplastic drugs since they can stimulate nonspecific effector mechanisms known to play a role in resistance against tumors.