Inducible cAMP early repressor (ICER) isoforms and neuronal apoptosis in cortical in vitro culture

CREB activation and CREB-dependent signaling pathways are crucial for neuronal survival. The term ICER (inducible cAMP early repressor) refers to four protein isoforms that are all endogenous, inducible antagonists of CREB. Jaworski and others (2003) have previously shown that one of those isoforms, ICER IIgamma, is highly expressed in apoptotic neurons in vitro and its overexpression evokes neuronal death. In this study we investigated the role of all four ICER isoforms in cortical neuronal culture, comparing their expression level in serum-deprived/MK-801-treated neurons and their pro-apoptotic properties towards transfected cortical neurons. We have found that all four isoforms are induced upon pro-apoptotic treatment, and also that each of them separately evokes neuronal cell death following cortical culture transfection with the genes. The most efficiently induced, as well as the most effective in evoking neuronal cell death, were both ICER Igamma and IIgamma isoforms.     

Quantitative theories of T-cell responsiveness

Summary:  We review recent advances toward a comprehensive mathematical theory of T-cell immunity. A key insight is that the efficacy of the T-cell response is best analyzed in terms of T-cell receptor (TCR) avidity and the distribution of this avidity across the TCR repertoire (the 'avidity spectrum'). Modification of this avidity spectrum by a wide range of tuning and tolerance mechanisms allows the system to adapt cross-reactivity and specificity to the challenge at hand while avoiding inappropriate responses against non-pathogenic cells and tissues. Theoretical models relate molecular kinetic parameters and cellular properties to systemic level statistics such as avidity spectra. Such bridge equations are crucial for rational clinical manipulation of T cells at the molecular level.     

Suppression of B-cell and T-cell responses by the prostaglandin-induced T-cell-derived suppressors (PITS)--III. Production of PITS beta factors from T-cell hybridomas

Previous studies have shown that the prostaglandin-induced T-cell-derived suppressors (PITS) are actually a mixture of at least seven distinct factors. These factors may be reproducibly resolved by size-exclusion chromatography followed by high-pressure liquid chromatography (HPLC). Results are presented here which suggest that two T-lymphocyte hybridoma clones are capable of constitutive synthesis of three of these suppressor factors. Results show that clone Hyb-7SC2 produces factors which co-elute (by HPLC) with the PITS beta2 and PITS beta3 factors, while clone Hyb-9SC2 produces a factor which co-elutes with PITS beta1. These results suggest the possibility that the seven PITS beta factors are not the product of a single cell population.     

Suppression of immune responsiveness by a submandibular salivary gland factor.

Both tissue extracts prepared from submandibular salivary glands of male mice and epidermal growth factor isolated from these glands depressed the delayed type hypersensitivity response to 2,4-dinitro-1-fluorobenzene in mice. Extirpation of the submandibular salivary glands from male mice did not alter the delayed type hypersensitivity response. The role of salivary gland factors, particularly epidermal growth factor, in influencing the immune response has been discussed.     

Evaluation of spleen lymphocyte responsiveness to a T-cell mitogen during early infection with larvalTaenia taeniaeformis

The effect of taeniid infection on the in vitro cellular response of the host was investigated. Infections ofTaenia taeniaeformis decreased the ability of spleen cells from susceptible C3H/He mice to respond to the T-cell mitogen concanavalin A (Con A) as early as 2 days postinfection (pi) reaching a suppression peak at day 12 pi. Similar experiments performed with spleen cells from infected BALB/c mice, resistant to the infection, revealed little or no suppression of Con A stimulation. The results suggested that susceptibility to the parasite may be due to its ability to induce a partial suppression of the host's immune system. The role of adherent splenocytes from infected C3H/He mice in the production of a deficient response to Con A during early infection was studied by coculturing experiments. These experiments demonstrated that adherent populations from infected mice did not play a direct role in the Con A-suppressor mechanisms. Concomitant with the suppressor activity an increased background proliferation was observed with nonstirnulated splenocytes from C3H/He mice infected withT. taeniaeformis. Plasma from infected mice was able to suppress the response of normal spleen cells to Con A and to stimulate a proliferative response in cultured splenocytes from noninfected animals. The results suggest the presence of factors in the plasma of infected mice which may be modulating the immune response to the parasite.     

Impact of inducible co-stimulatory molecule (ICOS) on T-cell responses and protection against Mycobacterium tuberculosis infection

Even though Mycobacterium tuberculosis (Mtb) remains one of the top microbial killers, more than 90% of the 2 billion infected individuals never develop active tuberculosis (TB), indicating efficient immune control of infection in these individuals. Immune mechanisms promoting either control or reactivation of TB are incompletely understood. Kinetic analyses of T-cell responses against Mtb in C57BL/6 mice revealed surface expression of inducible co-stimulatory molecule (ICOS) on >30% of all CD4(+) T cells, suggesting a pivotal role of this costimulatory molecule of the CD28 family in TB control. Surprisingly, Mtb-infected ICOS(-/-) mice showed lower bacterial burden during the late chronic stage of infection as compared to WT controls. ICOS deficiency resulted in a reduced Mtb-specific CD8(+) T-cell response during late-stage infection. In contrast, the polyclonal CD4(+) Th1 response against Mtb was increased, most likely caused by diminished numbers and frequencies of Tregs. Thus, by altering effector T-cell populations differentially, ICOS signaling modulates TB control in the late stage of infection.     

Suppression of T-cell responses to histocompatibility antigens by BCG pre-treatment.

The injection of 3 mg BCG into C57Bl/6 mice was followed 14 days later by a decrease in reactivity of spleen cells when engaged in mixed-lymphocyte reactions or in graft-versus-host reactions. In vitro, the lack of reactivity was due to an active suppression exerted mainly by the adherent population. In vivo, it was not possible to demonstrate active suppression.     

Suppression of polyclonal immunoglobulin biosynthesis by a soluble factor: T-cell dependent and T-cell independent mitogens

When normal human spleen cells are pulsed with concanavalin A (Con A), a portion become suppressor cells which in co-culture can inhibit immunoglobulin synthesis by other normal spleen cells stimulated by pokeweed mitogen (PWM). One mechanism whereby these Con-A activated spleen cells suppress Ig synthesis appears to be by the secretion of a soluble suppressor factor(s) since supernatants of Con-A stimulated splenocytes also suppress the polyclonal synthesis of immunoglobulin by human spleen cells. In this study, we report that supernatants of Con-A activated spleen cells suppress the in vitro synthesis of IgG, IgM and IgA by human spleen cells cultured with PWM. Our results indicate that the soluble suppressor factor(s) blocks an early stage in the differentiation of B lymphocytes into plasma cells without affecting the synthesis and secretion of immunoglobulin by more mature lymphocytes which appear to be irreversibly committed toward the pathway of synthesizing immunoglobulin. In addition, we studied the ability of normal human spleen cells to synthesize polyclonal immunoglobulin when cultured with either the T-cell dependent PWM or T-cell independent mitogens lipopolysaccharide (LPS) and Nocardia. Our results demonstrate that normal human splenic mononuclear cells cultured with either Nocardia, LPS or PWM are significantly stimulated to synthesize polyclonal IgG, IgM and IgA. Furthermore, supernatants of Con-A activated human spleen cells suppressed the polyclonal synthesis of these three antibody classes by human spleen cells responding to either T-cell dependent or independent mitogens.     

Suppression by Trypanosoma cruzi of T-cell receptor expression by activated human lymphocytes.

The immunosuppression that develops during Chagas' disease and African sleeping sickness is thought to facilitate survival of the causative agents in their mammalian hosts. Whereas a number of manifestations of immunosuppression manifested during the course of these diseases has been reported in patients and animals, the mechanisms by which they are induced remain obscure. An in vitro system in which phytohaemagglutinin (PHA)-stimulated human peripheral blood mononuclear (PBMC) were co-cultured with purified Trypanosoma cruzi or T. brucei rhodesiense was used in the present work to establish whether these organisms were able to alter the capacity of activated helper/inducer (CD4+) or cytotoxic/suppressor (CD8+) cells to express T-cell receptor (TcR). Suppressed interleukin-2 receptor (IL-2R), known to be caused by both the trypanosomes and supernatants containing their secretion products, was the independent parameter used to demonstrate the occurrence of immunosuppression in all experiments. We found marked reductions in the percentage of TcR+ cells in T. cruzi-containing cultures as early as 18 hr after PHA stimulation. This alteration was still readily demonstrable after 72 hr of culture, i.e. when last tested for. Suppressed TcR expression occurred concomitantly with reduced levels of CD4 or CD8 molecules on the surface of helper/inducer and cytotoxic/suppressor T lymphocytes, respectively, indicating that the parasite had induced more than one alteration in the same cells. These effects were reproduced when the trypanosomes were separated from the PBMC by a 0.45 micron pore size filter or when filtrates from T. cruzi suspensions substituted for the parasite in the cultures, indicating that TcR suppression was mediated by a parasite secretion product(s). Interestingly, neither T. b. rhodesiense nor filtrates of suspensions of this organism altered significantly the level of TcR expression in cultures in which suppressed IL-2R expression by activated human T cells took place. Thus despite sharing the ability to impair IL-2R expression, T. cruzi and T.b. rhodesiense appear to differ in other mechanisms by which they affect human T-cell function. If occurring in infected hosts, the alterations that T. cruzi causes in the expression of TcR, CD4, CD8 and IL-2R--all molecules playing important roles in lymphocyte activation--could contribute to the development of the immunosuppression observed during the acute phase of Chagas' disease.     

Suppression of contact sensitivity by a plastic adherent T-cell, induced in mice infected with Newcastle disease virus (NDV)

Previous studies have demonstrated that lymph node cells of mice skin-sensitized 24 h before are able to transfer contact sensitivity (CS) in naive recipients. These antigen presenting cells (APC) lose the ability to induce CS when donor mice are treated with the virus of Newcastle Disease (NDV) at the time of sensitization. In this paper we demonstrate that the cell capable of suppressing CS is a virus induced plastic adherent T-cell, which inhibits otherwise normal APC. In fact, the APC in infected mice are fully competent, as demonstrated by their ability to transfer CS, if the adherent T-cell population is removed by plastic adherence. Analysis shows that the CS suppressing adherent T-cells are Thy 1.2+, Lyt 1.1+ and I-J+ subset. The inhibition of CS by the NDV induced adherent T-cell is antigen non-specific and genetically restricted. We have also demonstrated that picrylated cells from NDV infected mice fail to trigger the release of non-specific inhibitor (nsINH) in the T-suppressor circuit. The effect of the adherent suppressor T-cell in that circuit was determined and the results indicate that the virus induced T-cell is able to suppress the release of nsINH by blocking the function of the APC.     

Modulation of polymorphonuclear leukocyte responsiveness by copper (II)2 (niflumate)4

Antiinflammatory activities and modulations of PMNL responses produced by treatment with tetrakis--2-[3-(trifluoromethyl)-phenyl] aminonicotinatodicopper (II) [Cu(II)₂(niflumate)₄] and niflumic acid were studied in isologous serum-induced rat pleurisy. Doses of 10 or 30 mg/kg (35 or 106 µmol/kg) of niflumic acid or Cu(II)₂ (niflumate)₄ (8 or 23 µmol/kg) caused significant (p < 0.01) reductions in pleural exudate and number of polymorphonuclear leukocytes (PMNLs) in the exudate. While both doses of Cu(II)₂(niflumate)₄ produced significant dose-related reductions in both parameters, only the higher dose of niflumic acid produced a significant dose-related reduction in both parameters. Boyden chamber measurements of N-formyl-methionyl-leucyl-phenylalanine (f-MLP) chemotaxis by PMNLs incubated with 10 or 30 µg/ml niflumic acid (35 or 106 nmol/ml) or Cu(II)₂(niflumate)₄ (8 or 23 nmol/ml) were significantly (p < 0.01 to p < 0.001) decreased in dose-related fashions. Chemotaxis of PMNLs from pleuritic rats treated orally with 10 or 30 mg/kg niflumic acid or Cu(II)₂(niflumate)₄ was significantly (p < 0.001) inhibited by the larger dose of niflumic acid and both doses of Cu(II)₂(niflumate)₄. Opsonized zymosan (OZ)-stimulated chemiluminescence (CL) of PMNLs from pleuritic rats treated orally with these same doses of niflumic acid or Cu(II)₂(niflumate)₄ was only significantly (p < 0.05 or p < 0.01 respectively) decreased by the larger doses. Superoxide (O ₂ ^- ) production by these cells was significantly decreased by the larger dose of niflumic acid (p < 0.05) while both doses of Cu(II)₂(niflumate)₄ produced significant (p < 0.05 to p < 0.01) decreases. Recovery of the decreased PMNL response in burned rats was also studied following treatment with these two compounds. Oral treatment of non-burned rats with 1 mg/kg niflumic acid (4 µmol/kg) or Cu(II)₂(niflumate)₄ (1 µmol/kg) did not affect OZ-stimulated O ₂ ^- production while decreased O ₂ ^- production in non-treated scald-burned rats was reversed by oral treatment with either niflumic acid or Cu(II)₂(niflumate)₄. It is concluded that Cu(II)₂(niflumate)₄ is a more effective antiinflammatory agent than niflumic acid and more effective modulation of PMNL responsiveness may explain its beneficial antipleuritic and burn-injury recovery effects. Formation of the copper complex of niflumic acidin vivo may also account for its beneficial antiinflammatory effects and recovery of depressed PMNL responsiveness in burned rats.     

Inhibition by human T-lymphotropic virus (HTLV-I) of T-lymphocyte mitogenesis: failure of exogenous T-cell growth factor to restore responsiveness to lectin.

Various retroviruses, including human T-cell lymphotropic virus (HTLV-I) and avian sarcoma virus (ASV), can prevent coincubated human peripheral lymphocytes from responding efficiently to phytohaemagglutinin. Addition of high concentrations of T-cell growth factor (TCGF) activity usually overcomes this inhibition. However, such restoration of responsiveness does not occur in the case of HTLV-coincubated cells.