Role of T-cell derived cytokines in the downregulation of immune responses in parasitic and retroviral infection

Nitric oxide synthesis is depressed in Bos indicus cattle infected with Trypanosoma congolense and Trypanosoma vivax and does not mediate T-cell suppression

Infection with African trypanosomes causes the diseases sleeping sickness in humans and nagana in cattle in sub-Saharan Africa. Suppression of cellular immune responses is a feature of trypanosomiasis in bovine, human, and murine hosts. Some aspects of immunosuppression in the murine model are mediated by nitric oxide (NO) produced by gamma interferon (IFN-gamma)-activated macrophages. We have investigated whether a similar mechanism is responsible for T-cell unresponsiveness in bovine trypanosomiasis. Bovine monocytes and macrophages from uninfected cattle and activated in vitro with IFN-gamma produced NO; however, this response was down-regulated in infected cattle. Similarly, the expression of inducible NO synthase messenger RNA was depressed in macrophages of infected cattle. Proliferation of mononuclear cells of trypanosome-infected cattle cultured with mitogen or trypanosome antigens was unchanged by the addition of an NO synthase inhibitor. Lymphocytes of infected cattle secreted interleukins with T-cell growth factor activity after in vitro activation with mitogens but not after activation with trypanosome antigens. Although lymph node cells secreted IFN-gamma after in vitro activation, ex vivo expression of mRNA was depressed. In contrast, the level of expression of interleukin 10 mRNA was higher during infection. We conclude that NO is not involved in the loss of T-cell proliferative function associated with trypanosomiasis in cattle and that, in contrast to the mouse model, the capacity of monocytes and macrophages to produce NO is actually down-regulated in infected cattle.

Transcriptional regulation of human polyomavirus JC: evidence for a functional interaction between RelA (p65) and the Y-box-binding protein, YB-1

The transcriptional control region of the human neurotropic polyomavirus JC virus contains a consensus NF-kappa B site which has been shown to enhance both basal and extracellular stimulus-induced levels of transcription of JC promoters. Here, we show that the expression of JC late promoter constructs containing the NF-kappa B site is decreased by cotransfection with the NF-kappa B/rel subunits, p50 and p52, but enhanced by the p65 subunit. However, JC promoter constructs lacking the NF-kappa B site were activated by p52 and p50 and repressed by p65. This antithetical response of the JC promoter mapped specifically to the D domain, which is a target site for the cellular transcription factor, YB-1. Band shift studies indicated that YB-1 and p65 modulate each other's binding to DNA: YB-1 augments the affinity of p65 for the NF-kappa B site, while p65 reduces the binding of YB-1 to the D domain. Results from coimmunoprecipitation followed by Western blot (immunoblot) analysis suggest an in vivo interaction between p65 and YB-1 in glial cells. Functionally, YB-1 appears to act synergistically with p65 to control transcription from the NF-kappa B site. A converse pattern is seen with the D domain, in which YB-1 acts synergistically with p50 and p52 to regulate transcription. p50 and p52 may function as transcriptional activators on the D domain by removing the repressive effect of p65 on YB-1 binding to the D domain. On the basis of these data, we propose a model in which NF-kappa B/rel subunits functionally interact with consensus NF-kappa B sites or YB-1-binding sites, with disparate effects on eukaryotic gene expression.

IL-4-deficient Balb/c mice resist infection with Leishmania major

Mice with a genetically engineered deficiency for either IL-4 or IFN-gamma R1 (single mutants), and IL-4/IFN-gamma R1 (double mutants) on the Balb/c and 129Sv background were used to study the course of infection with Leishmania major. In contrast to genetically resistant 129Sv wildtype mice, IL-4/IFN-gamma R1 double mutant mice developed fetal disease with parasite dissemination to visceral organs similar to mice lacking IFN-gamma R1 only. Balb/c mice, which are exquisitely susceptible to L. major, were rendered resistant to infection by disruption of the IL-4 gene. As compared to homozygous IL-4+/- mice, heterozygous IL-4+/- mice, heterozygous IL-4+/- animals consistently developed smaller lesions with less ulceration and necrosis, indicating the likelihood of gene-dosage effects. This implicates that the magnitude of the IL-4 response determines the severity of disease. CD4+ T cells of IL-4-deficient mice showed impaired Th2 cell development, as assessed by quantitative RT-PCR of characteristic cytokines. Development of resistance is not explained by default Th1 development, because this was observed only at very late stages of infection. Moreover, the induction of inflammatory cytokines (e.g., IL-1 alpha, IL-1 beta, TNF-alpha, IL-12) together with iNOS in the lesion and draining lymph nodes was not altered in the absence of IL-4.

Soluble factors secreted by activated T-lymphocytes modulate the transcription of the immunosuppressive cytokine TGF-beta 2 in glial cells

Coordination of the immune response to injury or disease in the brain is postulated to involve bi-directional discourse between the immune system and the central nervous system. This cross communication involves soluble mediators, including various growth factors, cytokines, and neuropeptides. In this report, we demonstrate that the supernatant from activated T-lymphocytes is able to induce the transcription of a potent cytokine, TGF-beta 2 in glial cells. The activating stimulus invokes signaling mechanisms distinct from known kinase or protease pathways. Activation of TGF-beta 2 transcription correlates with the loss of binding activity for an 80 kDA glial labile repressor protein, GLRP, to a responsive region within the TFG-beta 2 promoter. Although GLRP shares some characteristics with the inducible transcription factor AP-1, it appears to be distinct from known AP-1 family members. These data along with previous observations demonstrating the potent immunosuppressive activity of TGF-beta 2, support a model for a feedback mechanism between the activated T-lymphocytes and astrocytes via TGF-beta 2 to regulate the immune response.

The functional half-life of H-2Kd-restricted T cell epitopes on living cells

The functional half-life (t1/2) of different complexes formed by major histocompatibility complex (MHC) class I molecules and antigen on the surface of target cells was measured using specific cytotoxic T lymphocyte (CTL) clones in cytolysis, and interferon-gamma-production and Ca(2+)-mobilization assays. Functional t1/2 values of 5-10 h were obtained, which are in accordance with some previous estimations obtained from biochemical and immunochemical measurements. Moreover, these values were independent of the type of target cell, fixation of the target cells, or proteases able to degrade the peptides, suggesting that the unfolding of the peptide/MHC complexes at the cell surface alone determines the functional t1/2 of the CTL epitopes.

Cytokines in infectious diseases

Cytokines are heterogeneous group of proteins that are produced by a wide variety of cells in the body and act as signals between the cells of the immune system. The recent discovery of two distinct subsets of T-helper cells led to the development of a conceptual framework of complex network of cytokine pathways in the regulation of immune responses against a variety of infectious agents. In this brief review, we have attempted to present a concise summary of the current state of knowledge of this complex interaction among cytokines that result in a cascade of biological events leading to inflammatory response and host defense against pathogens.

A critical role for transforming growth factor-beta but not interleukin 4 in the suppression of T helper type 1-mediated colitis by CD45RB(low) CD4+ T cells

A T helper type 1 (Th1)-mediated colitis with similarities to inflammatory bowel disease in humans developed in severe combined immunodeficiency mice reconstituted with CD45RB(high) CD4+ splenic T cells and could be prevented by cotransfer of CD45RB(low) CD4+ T cells. Inhibition of this Th1 response by the CD45RB(low) T cell population could be reversed in vivo by an anti-transforming growth factor (TGF) beta antibody. Interleukin (IL) 4 was not required for either the differentiation of function of protective cells as CD45RB(low) CD4+ cells from IL-4-deficient mice were fully effective. These results identify a subpopulation of peripheral CD4+ cells and TGF-beta as critical components of the natural immune regulatory mechanism, which prevents the development of pathogenic Th1 responses in the gut, and suggests that this immunoregulatory population is distinct from Th2 cells.

Mice infected with the larvae of Taenia crassiceps exhibit a Th2-like immune response with concomitant anergy and downregulation of Th1-associated phenomena

Infection of intermediate hosts with eggs of taeniid parasites results in a larval infestation known as cysticercosis. A number of studies have indicated that cysticercosis is associated with immunosuppression, although little is known about the mechanisms involved. In the present study, mice infected with the larvae of Taenia crassiceps were found to exhibit a pronounced energy, which preferentially affected T-cells located anatomically close to the parasite. This anergy was linked to late events in the T cell activation pathway; that is, stimulation through the T cell receptor(TCR)/CD3 complex by Concanavalin-A, or plate-bound monoclonal antibodies (mAb) to TCR alpha beta or CD3 epsilon, or combinations of phorbol ester and ionomycin (all of which can bypass early membrane-related events), failed to fully activate T lymphocytes. The relative proximity of T cells to the parasite was directly related to upregulation of IL-4 and downregulation of IL-2 production. In addition, the profiles of parasite-specific Abs showed an exclusive increase of serum IgG1 during infection. Taken together, the data suggest that infection of mice with larvae of T. crassiceps alters the balance of CD4+ Th cells by upregulating Th2 and downregulating Th1 cells located in close proximity to the parasite.

Regulation of disease susceptibility: decreased prevalence of IgE-mediated allergic disease in patients with multiple sclerosis

The development of restricted cytokine profiles by subsets of CD4+ T cells is a pivotal point in the regulation of immune responses. T cells producing Th1 cytokines (IL-2 and interferon-gamma) induce cell-mediated immunity, whereas T cells producing Th2 cytokines (IL-4, IL-5, and IL-10) play a prominent role in the induction of humoral immunity. We examined a group of patients with multiple sclerosis, a disease caused by excess production of Th1 cytokines in myelin-reactive T cells, and control patients with noninflammatory neuroconvulsive disorders, for the presence of allergic disease, which is caused by excess production of Th2 cytokines in allergen-specific T cells. The patients with multiple sclerosis had significantly fewer allergic symptoms, a lower number of positive allergen-specific IgE test results, and lower composite allergy indexes than control subjects. These results demonstrate that the prevalence of IgE-mediated allergic disease is decreased in a group of patients with multiple sclerosis and support the hypothesis that genetic factors that promote susceptibility to Th1-mediated inflammatory disease in human beings protect against the development of Th2-mediated disease.

Induction of protective CTL responses in newborn mice by a murine retrovirus

The susceptibility of neonates to virus-induced disease is thought to reflect, in part, the immaturity of their immune systems. However, inoculation of newborn mice with low doses of Cas-Br-M murine leukemia virus induced a protective cytotoxic T lymphocyte (CTL) response. The inability of neonates to develop a CTL response to high doses of virus was not the result of immunological immaturity but correlated with the induction of a nonprotective type 2 cytokine response. Thus, the initial viral dose is critical in the development of protective immunity in newborns.

Candidate HIV type 1 multideterminant cluster peptide-P18MN vaccine constructs elicit type 1 helper T cells, cytotoxic T cells, and neutralizing antibody, all using the same adjuvant immunization

Cytotoxic T lymphocytes and Th1 cells have been suggested to play a critical role in the control of HIV infection. It is therefore considered that a vaccine that induces a strong Th1 response and CTL response would be more efficacious than one that does not in providing protection against infection and progression toward AIDS. In this study we show that immunization with vaccine constructs consisting of multideterminant cluster peptides containing Th epitopes from the HIV-1IIIB envelope colinearly synthesized to peptide 18MN, is capable of inducing a Th1 response in mice and, dependent on this help, both cytotoxic T cell responses and neutralizing antibody toward the homologous strain of HIV. Moreover, the cytotoxic T cell response elicited by immunization with a mixture of cluster peptide-P18MN vaccine constructs was at least as cross-reactive against known viral variant P18 target sequences as a CTL line produced by immunization with a vaccinia construct expressing recombinant gp160 MN. Four adjuvants were compared to optimize both CTL and antibody responses. A single adjuvant formulation of peptide in ISA 51 could elicit all three: Th1 cells, CTLs, and neutralizing antibody. Thus, immunization directed toward the development of a cytotoxic T cell response does not preclude the development of neutralizing antibody and vice versa, i.e., the responses are not mutually exclusive. The immunization protocol described here should be directly applicable for study in clinical trials aimed at HIV-1 immunotherapy or prophylaxis.

Graft-versus-host disease and the Th1/Th2 paradigm

Graft-versus-host disease (GVHD) is the major complication after allogeneic bone marrow transplantation (BMT) and is initiated by alloreactive donor T cells recognizing foreign histocompatibility antigens of the host. There is now substantial experimental and clinical evidence to implicate a dysregulation of cytokine networks as a primary cause for the induction and maintenance of GVHD. In this article, current knowledge of the involvement of cytokines in GVHD is reviewed. The balance between type 1 cytokines (interleukin-2, interferon-gamma) and type 2 cytokines (interleukin-4, interleukin-10) is hypothesized to govern the extent to which a cell-mediated immune response and a systemic inflammatory response develop after allogeneic BMT. Because type 2 cytokines can inhibit the production of the proinflammatory cytokines interleukin-1 and tumor necrosis factor-alpha, a type 1 to type 2 shift in the initial response of donor T cells to host alloantigens may interrupt the cytokine cascade after allogeneic BMT and may offer a new approach to the prevention and treatment of acute GVHD. Interventions to specifically eliminate or modify the response of donor T cells to alloantigens in order to reduce GVHD may obviate the need for T cell depletion in clinical BMT and thus avoid the increased risk of relapse of malignancy and impairment of donor cell engraftment.

2-Carboxyethylgermanium sesquioxide, a synthetic organogermanium compound, as an inducer of contrasuppressor T cells

2-Carboxyethylgermanium sesquioxide (Ge-132), a synthesized organogermanium compound with immunomodulating activities, was shown to be an inducer of anti-suppressor T cells in normal mice. The suppressor cell activity of T6S cells, a clone of burn-induced CD8+ IL-4-producing suppressor T cells, was clearly inhibited when a mixed lymphocyte-tumor cell reaction of the clone was conducted with splenic mononuclear cells from mice treated orally with a 100 mg/kg dose of Ge-132. The activity of anit-suppressor cells was demonstrated in spleens of mice 2 days after treatment with Ge-132 and reached its peak on day 3. The anti-suppressor cells induced by the compound were of a contrasuppressor T cell-linage, because they were characterized as CD4+ CD28+ TCRalpha/beta+ Vicia villosa lectin-adherent T cells. These cells produced IFN-gamma but did not produce IL-2, IL-4, IL-6 or IL-10 in their culture fluids. CD4+ anti-suppressor T cells induced by Ge-132 may be different from other subsets of CD4+ T cells because Th1 and Th2 cells generated in our laboratory did not adhere to Vicia villosa lectin-coated petri dishes, and each produced specific cytokines. Th1 cells produced IFN-gamma and IL-2 while Th2 cells produce IL-4 and IL-10 in vitro. These results suggest that Ge-132 may be useful as an inducer of contrasuppressor T cells in immunocompromised individuals bearing suppressor T cells. To eliminate suppressor T cells from immunocompromised hosts may result in improved resistance from various opportunistic infections.

Selective development of T helper (Th)2 cells induced by continuous administration of low dose soluble proteins to normal and beta(2)-microglobulin-deficient BALB/c mice

Continuous administration of soluble proteins, delivered over a 10-d period by a mini-osmotic pump implanted subcutaneously, induces a long-lasting inhibition of antigen-specific T cell proliferation in lymph node cells from BALB/c mice subsequently primed with antigen in adjuvant. The decreased T cell proliferative response is associated with a down-regulation of the T helper cell (Th)1 cytokines interleukin (IL)-2 and interferon (IFN)-gamma and with a strong increase in the secretion of the Th2 cytokines IL-4 and IL-5 by antigen specific CD4+ T cells. This is accompanied by predominant inhibition of antigen-specific antibody production of IgG2a and IgG2b, rather than IgG1 isotype. Interestingly, inhibition of Th1 and priming of Th2 cells is also induced in beta(2) microglobulin-deficient BALB/c mice, indicating that neither CD8+ nor CD4+ NK1.1+ T cells, respectively, are required. The polarization in Th2 cells is stably maintained by T cell lines, all composed of CD4+/CD8- cells expressing T cell receptor for antigen (TCR) alpha/beta chains, derived from BALB/c mice treated with continuous antigen administration, indicating that they originate from Th2 cells fully differentiated in vivo. This polarization is induced in BALB/c mice by continuous administration of any protein antigen tested, including soluble extracts from pathogenic microorganisms. Priming of Th2 cells is dose dependent and it is optimal for low rather than high doses of protein. Blocking endogenous IL-4 in vivo inhibits expansion of antigen-specific Th2 cells, but does not restore IFN-gamma production by T cells from mice treated with soluble antigen-specific Th2 cells, but does not restore IFN-gamma production by T cells from mice treated with soluble antigen, indicating the involvement of two independent mechanisms. Consistent with this, Th2 cell development, but not inhibition of Th1 cells, depends on non-major histocompatibility complex genetic predisposition, since the Th2 response is amplified in BALB/c as compared to DBA/2, C3H, or C57BL/6 mice whereas tested. These findings support the hypothesis that continuous release of low amounts of protein antigens from pathogenic microorganisms may polarize the immune response toward a Th2 phenotype in susceptible mouse strains.

[Strongyloides stercoralis in T-cell leukemia/lymphoma in adults and acquired immunodeficiency syndrome]

The mechanisms of chronic infestation by Strongyloides stercoralis (Ss) are unknown. Immunodepression is classically evoked to explain the proliferation of the parasite that is sometimes massive and overwhelming. We present here two retrospective studies of 13 cases of strongyloidiasis (three disseminated strongyloidiasis) out of 26 patients with adult T-cell leukemia/lymphoma (ATL) and of ten cases of strongyloidiasis out of 98 patients with AIDS. Ten patients out of 98 were dually infected with both HIV and HTLV-1: 2/10 also infected by Ss. The frequency of Ss infection appears higher in ATL patients when compared with AIDS patients (P < 0.001). Ss-infected ATL patients were younger than those uninfected (P < 0.01). Ss-infected AIDS patients were older than the ones uninfected (p < 0.03). No significative difference was found between ATL and AIDS patients who were over 40 years-old. These data suggest that 1) the particular type of immunodepression produced early by HTLV-1 is more favorable to the development of Ss infection than the one associated with HIV, 2) the latency of expression of HTLV-1, prior to the development of leukemia, is reduced in Ss-infected patients, 3) Ss infection may slow down VIH pathogenic activity.

T-cell-receptor dose and the time of treatment during murine retrovirus infection for maintenance of immune function

C57BL/6 mice were injected with different doses of human T-cell receptor (TCR) V beta 8.1 CDR1 peptide at different times after murine retrovirus (LP-BM5) infection. Injection with TCR V beta 8.1 CDR1 peptide largely prevented the retrovirus-induced reduction in B- and T-cell proliferation, and T-helper 1 (Th1) cytokines [interleukin-2 (IL-2) and interferon-gamma (IFN-gamma)] secretion. It also suppressed T-helper 2 (Th2) cytokines (IL-6 and IL-10) production, which was stimulated by retrovirus infection. These effects were accomplished using at least 100 micrograms of peptide per mouse and the most effective dose of peptide had to be given within 4 weeks after retrovirus infection. Immunization with doses above 100 micrograms/mouse as long as 4 weeks postinfection maintained natural killer (NK) cell activity during retrovirus infection. Reducing the dose of peptide or delaying it until the disease progressed towards early murine acquired immune deficiency syndrome (AIDS) allowed development of immune dysfunction. These studies provide data suggesting that immune dysfunction, induced by murine retrovirus infection, was largely prevented by TCR V beta CDR1 peptide injection.

Murine AIDS, a key to understanding retrovirus-induced immunodeficiency

A murine AIDS model, induced by LP-BM5 murine leukemia virus (MuLV), has helped to investigate pathogenesis of acquired immunodeficiency syndrome (AIDS), cofactor involvement, and new treatment tests. LP-BM5 MuLV-infected mice characteristically develop hypergammaglobulinemia, splenomegaly, lymphadenopathy, T-cell functional deficiency, B-cell dysfunction, and, in the later stages, neurological signs including paralysis as well as susceptibility to opportunistic infections. The similarities between murine AIDS and human AIDS are striking, with similar changes in immune functions, T-cell differentiation, cytokine production, disease resistance, and oxidative stress. The well-characterized murine immunological system, availability of inbred strains, economy of using mice versus primate model, and similarities in immunodeficiency caused by human immunodeficiency virus (HIV) encouraged rapid development of the LP-BM5 murine AIDS model in the past decade.

Involvement of excretion-secretion products from Fasciola hepatica inducing suppression of the cellular immune responses

Normal rats i.p. injected with Fasciola hepatica excretor-secretor antigen (ESA) induced a population of spleen mononuclear (SpM) cells, which suppressed the delayed type hypersensitivity (DTH) response to parasite antigens as well as to non-related antigens (human serum albumin) by adoptive transfer. A similar effect was observed when the cell transfer was performed with SpM cells non-adherent to nylon wool. The DTH was not modified by cells transfer adherent to nylon wool in syngeneic receptor animals. The observed suppression depended on the concentration and inoculation moment of the antigen; 1.8 mg of protein ESA being enough to suppress the DTH response at the different days studied, before and after immunization with whole F. hepatica antigens. A marked suppression was observed when ESA was injected on day 7 pre-immunization. On the other hand, inoculation of ESA treated with 0.01 M sodium periodate (carbohydrate oxidant) diminished the suppressor effect found after the native ESA inoculation, indicating participation of ESA glucidic components in induced suppression. Inoculation of ESA fractions obtained from polyacrylamide gel elution with different MW range, showed that components between 12 and 23 kDa actively induced suppression to the DTH response to parasite antigens.

In vivo direction of CD4 T cells to Th1 and Th2-like patterns of cytokine synthesis

Factors that influence the initial development, and continued maintenance, of Th1 or Th2-like responses in vivo play a pivotal role in determining immune effector mechanisms and clinical outcome. Here, we review recent developments in this area with particular emphasis on (i) the ability of chemically modified exogenous antigens to preferentially activate Th1-dominated responses in vivo and (ii) the role played by NK cells in initial commitment of naive exogenous antigen-specific T cells to Th1 or Th2-like cytokine synthesis. We find that NK cell depletion of naive mice prior to immunization with OVA (which induces balanced Th0 like responses), or a high Mr polymer (that preferentially elicits OVA-specific Th1-dominated responses), fails to influence the development of cytokine or specific antibody responses. The results argue that NK cells do not play an essential role in shaping induction of immune responses to exogenous antigens, the most common class of inhalant allergen.

Immunomodulation by pycnogenol in retrovirus-infected or ethanol-fed mice

Pycnogenol is a commercial mixture of bioflavonoids that exhibits antioxidative activity. The effects of dietary pycnogenol on immune dysfunction in normal mice as well as those fed ethanol or infected with the LP-BM5 murine retrovirus were determined. The ethanol consumption and retrovirus infection caused abnormalities in the function and/or structure of a broad array of cells involved in humoral and cellular immunity. Pycnogenol enhanced in vitro IL-2 production by mitogen-stimulated splenocytes if its production was suppressed in ethanol-fed or retrovirus-infected mice. Mitogenesis of splenocytes did not show a significant change in mice treated with pycnogenol. It reduced the elevated levels of interleukin-6 produced in vitro by cells from retrovirus infected mice and IL-10 secreted by spleen cells from mice consuming ethanol. Natural killer cell cytotoxicity was increased with pycnogenol treatment.

Extent of T cell receptor ligation can determine the functional differentiation of naive CD4+ T cells

Naive CD4+ T cells can differentiate into cells predominantly involved in humoral immunity, known as T helper type 2 cells (Th2), or cells involved in cell-mediated immunity, known as Th1 cells. In this report, we show that priming of CD4+ T cells bearing a transgene-encoded T cell receptor can lead to differentiation into Th1-like cells producing abundant interferon gamma when the cells are exposed to high antigen doses, while low doses of the same peptide induce cells with the same T cell receptor to differentiate into Th2-like cells producing abundant interleukin 4. Thus antigen dose is one factor that can control the differentiation fate of a naive CD4+ T cell.

Interleukin (IL) 4, in the absence of antigen stimulation, induces an anergy-like state in differentiated CD8+ TC1 cells: loss of IL-2 synthesis and autonomous proliferation but retention of cytotoxicity and synthesis of other cytokines

Naive T cells in the periphery mainly secrete interleukin (IL) 2 upon activation. After stimulation in the presence of appropriate costimulators, both CD4+ and CD8+ T cells differentiate into effector cells secreting distinct T helper (Th) 1- and Th2-like cytokine patterns. Subsequent to differentiation, both CD4+ (Th1 and Th2) and CD8+ (TC1 and TC2) cells are stable and cannot be induced to differentiate into the opposite pattern or revert to the naive cytokine secretion pattern. We now show that IL-4 caused committed TC1 bulk populations or clones to lose the ability to synthesize IL-2. The cells retained the ability to secrete interferon (IFN) gamma, granulocyte/macrophage colony-stimulating factor, and tumor necrosis factor, did not synthesize any Th2 cytokines, and did not alter cell surface marker expression. IL-4 rapidly inhibited IL-2-synthesizing ability in the absence or presence of antigen-presenting cells, thus demonstrating that IL-4 acted directly on TC1 cells. The defect in IL-2 synthesis could not be reversed by subsequent stimulation with potent antigen-presenting cells in the presence of IL-2 and anti-IL-4, or with anti-CD3 plus anti-CD28 antibodies. Both IL-2+ and IL-2- TC1 cells were strongly cytotoxic toward allogeneic but not syngeneic targets. However, IL-2- TC1 cells were unable to proliferate unless exogenous IL-2 was provided. TC1 cells that lose IL-2 synthesis but retain IFN-gamma synthesis and cytotoxicity may be similar to the "anergic" cells induced by stimulation of CD4+ or CD8+ cells in the absence of costimulators. These results suggest that during a mixed type 1/type 2 response in vivo, IL-4 may induce the IL-2+ TC1-->IL-2-TC1 conversion, and thus curtail the expansion of the TC1 response without impairing short-term effector function.

Cytokines in the acquired immunodeficiency syndrome and other infectious diseases

The pathogenesis of several infectious diseases is frequently related not only to their etiological agents of viral, bacterial, or parasitic nature, but also to the host immune response. Both inflammatory responses and specific immune responses to the invading microorganisms are controlled by complex networks of intercellular signalling molecules, namely cytokines. This rapidly growing family of mediators includes lymphokines, interleukins, and molecules such as tumor necrosis factors and interferons. Patterns of cytokine production from antigen- or allergen-specific T lymphocytic cell clones have been identified, firstly in animal models and subsequently in man, and are commonly referred to as TH0, TH1, and TH2 profiles. The predominance of one of these profiles strongly influences the type of immune response (humoral versus cellular) and, at least in some experimental models, whether the immune response is protective or harmful. This is most convincingly demonstrated in models of parasitic diseases, but has also been hypothesized to be involved in the pathogenesis of human immunodeficiency virus infection and the acquired immunodeficiency syndrome. Earlier studies on human immunodeficiency virus infection revealed that the replicative capacity of this retrovirus, like the herpes viruses, is strongly influenced by the cytokine milieu of infected cells. Transcriptional and post-transcriptional regulation of human immunodeficiency virus expression by human cytokines are examples of the complex interdigitation of viruses with the host immune system.

Roles of gamma interferon and interleukin-4 in genetically determined resistance to Coccidioides immitis

The profiles of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) production were evaluated during the course of coccidioidomycosis in two inbred mouse strains which differ in their susceptibility to Coccidioides immitis. Cytokine responses, measured at the molecular and protein levels, showed increased levels of IFN-gamma in lung extracts from mice of the resistant DBA/2 strain after a pulmonary challenge, whereas the susceptible BALB/c strain manifested a predominant IL-4 response. The importance of these cytokines in host defense against C. immitis was established by treating the mice with recombinant cytokines or neutralizing anticytokine monoclonal antibodies. Treatment of the susceptible BALB/c mice with recombinant murine IFN-gamma significantly protected mice against systemic challenge, and in the reciprocal experiment, the administration of an anti-IFN-gamma monoclonal antibody to the resistant DBA/2 mice significantly decreased their capacity to control disease. Although the treatment of DBA/2 mice with recombinant IL-4 did not alter the disease, neutralization of endogenous IL-4 in infected BALB/c mice by administration of a neutralizing anti-IL-4 antibody led to a significant reduction in the fungal load in their tissues. These results, taken together, establish that IFN-gamma plays a pivotal role in resistance to C. immitis, whereas IL-4 down-regulates protective immunity against C. immitis.

Immunotolerance and prevention of ocular autoimmune disease

Immunotherapeutic approaches to autoimmune disease have a common goal of inducing antigen-specific, long-lasting tolerance to autoantigens, without otherwise compromising the immune response. Here we review some of the most interesting experimental advances in this area. We discuss the use of T cell targeting drugs that have been reported to induce long lasting tolerance to ocular antigens. Strategies involving the targeting of idiotypic and clonotypic determinants associated with ocular autoimmunity, such as idiotypic network manipulation and T cell vaccination, are reviewed. The use of cytokines to promote perturbation of the Th1/Th2 balance with its possible implications for treatment of uveitis, is analysed. Finally, we review tolerogenic strategies based on acquisition of tolerance following presentation of antigen through alternative routes, such as injection of antigen into the anterior chamber, intravenous infusion of antigen, and oral administration of retinal antigens. Special emphasis is placed on the last strategy, since there are ongoing clinical trials using oral tolerance as an immunotherapeutic approach to treat autoimmune diseases, among them uveitis.

Identification of Babesia bovis merozoite antigens separated by continuous-flow electrophoresis that stimulate proliferation of helper T-cell clones derived from B. bovis-immune cattle

To characterize Babesia bovis merozoite antigens that stimulate anamnestic T helper (Th)-cell responses from B. bovis-immune cattle, B. bovis-specific Th-cell lines and clones, previously assigned to different antigenic groups (W. C. Brown, S. Zhao, A. C. Rice-Ficht, K. S. Logan, and V. M. Woods, Infect. Immun. 60:4364-4372, 1992), were tested in proliferation assays against fractionated merozoite antigens. The antigenic groups were determined by the patterns of response of Th clones to different parasite isolates and soluble or membrane forms of merozoite antigen. Soluble antigen fractionated by anion-exchange chromatography or gel filtration by using fast-performance liquid chromatography resolved two or three antigenic peaks, respectively. To enable fractionation of membrane-associated proteins and to resolve more precisely the proteins present in homogenized merozoites, a novel technique of continuous-flow electrophoresis was employed. Merozoite membranes or whole merozoites were homogenized and solubilized in sodium dodecyl sulfate-sample buffer, electrophoresed under reducing conditions on 15% or 10% acrylamide gels, eluted, and collected as fractions. Individual fractions were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tested for the ability to stimulate Babesia-specific CD4+ T-cell lines and clones. CD4+ Th-cell lines from two cattle displayed differential patterns of reactivity and detected numerous peaks of antigenic activity, ranging from < 14 to 76 kDa. Th-cell clones previously categorized into different antigenic groups detected antigenic peaks unique for clones representative of a given group. Antigens of 29, 51 to 52, and 85 to 95 kDa (group I), 40 kDa (group III), 20 kDa (group IV), 58 to 60 kDa (group VI), and 38, 45, and 83 kDa (group VII) were identified in the stimulatory fractions. Immunization of rabbits with selected fractions produced a panel of antisera that reacted specifically on Western blots (immunoblots) with merozoite antigens of similar sizes, leading to the tentative identification of candidate antigens of B. bovis merozoites with molecular masses of 20, 40, 44, 51 to 52 or 95, and 58 to 60 kDa that stimulate proliferation of Th clones representative of five different antigenic groups. These antisera may be useful for isolating recombinant proteins that are immunogenic for Th cells of immune cattle and therefore potentially useful for vaccine development.

Modulation of disease activity in murine systemic lupus erythematosus by cytokine gene delivery

Somatic gene therapy is a novel approach with the potential to achieve prolonged increases in circulating levels of peptide hormones and cytokines. The present study evaluates the effects of monthly, intramuscular injections of cDNA expression vectors encoding for transforming growth factor beta (TGF beta) or interleukin 2 (IL-2) on disease activity in the MRL/lpr/lpr murine model of systemic lupus erythematosus (SLE). Monthly injections of plasmids cDNA between 6 and 26 weeks significantly elevated the serum levels of TGF beta (P < 0.005) and IL-2 (P < 0.05) compared with a control plasmid without insert. TGF beta encoding plasmid had beneficial effects in murine SLE with a prolonged survival of 70% at 26 weeks compared with 40% in the control group, decreased anti-chromatin and rheumatoid factor antibodies and a 50% decrease in total IgG production. Renal function was improved with reduced BUN levels and kidney inflammation as estimated by an histologic score. Those beneficial effects occurred in the apparent absence of local or systemic side-effects. In contrast, IL-2 cDNA injections appeared harmful with a decreased survival to 20% at 26 weeks, enhanced total IgG synthesis and autoantibodies production with a 4.5-fold increase in antichromatin antibodies. These results indicate that somatic gene therapy may provide a simple, inexpensive and effective mechanism for the long-term control of autoimmune diseases.

Immunoregulation in human lymphatic filariasis: the role of interleukin 10

In humans with lymphatic filariasis microfilaremia is associated with a parasite antigen-specific hyporesponsiveness when assessed by cell proliferation and secretion of interleukin-2 and interferon-gamma. Hyporesponsiveness in these individuals is not only parasite antigen-specific but appears to be limited to Th1-type responses. Th2 mediated responses such as IL-5 secretion and IgE antibody production to parasite antigens are generally strong and usually no different than those seen in immunologically more reactive amicrofilaremic individuals with chronic lymphatic pathology. The mechanisms by which Th1 responses are inhibited have not yet been elucidated, but some studies suggest that down-regulatory cytokines such as IL-10 may be involved in this process. Mononuclear cells from microfilaremic individuals have been found to secrete greater quantities of IL-10 spontaneously and in response to parasite antigens. In this review, mechanisms by which IL-10 may be induced by the parasite and the mode by which IL-10 may regulate parasite antigen-specific Th1 responses in these individuals are discussed.

Environmental lighting alters the infection process in an animal model of AIDS

In this study, we examined the effects of altered environmental lighting on the infection process of a murine leukemia virus, E-55(+), which induces a thymic lymphoma/leukemia in 100% of BALB.K mice inoculated as adults. One to two weeks after inoculation, high levels of proviral DNA are usually found. This is followed by an asymptomatic period of many weeks during which proviral DNA becomes essentially undetectable. Leukemia develops approximately 28 weeks postinoculation. In this experiment, one group of mice was exposed a consistent 10L: 14D cycle while a second was maintained in constant light (LL). A third group was exposed to a rotating cycle characterized by phase shifting a 10L: 14D cycle every three 24-h days (rLD). All cycles began 2 weeks prior to inoculation and were maintained thereafter. Animals were sacrificed at 1, 5, 10, and 15 weeks, and hematopoietic tissue was examined for proviral DNA content. At 1 week, LL- and rLD-exposed animals showed considerably less proviral DNA in bone marrow and spleen compared with controls. At 15 weeks, thymuses from controls were showing signs of infection whereas tissue from LL and rLD mice remained at background levels. We conclude that environmental lighting does alter the infective pattern displayed by this retrovirus, although whether this effect is mediated by changes in the target stem cells or through immunoenhancement has not yet been determined.

CD8+ type-2 T cells enhance the severity of acute herpes virus infection in mice

The role of CD8+ suppressor T cells in acute herpes simplex virus type 1 (HSV) infection was investigated in mice. CD8+ CD11b+ TCR-gamma/delta + suppressor T cells (HSV-STC) were demonstrated in spleens of mice infected intraperitoneally (i.p.) with HSV. When HSV-STC from mice infected with a 10 LD50 of HSV (donors) were adoptively transferred to mice 3 days after being infected with a 1 LD50 dose of HSV (recipients), the morbidity and mortality of recipients were greatly increased (mean survival time in days (MSD): 9.4 days; mortality, 100%) as compared with controls that received CD4+ T cells or a whole T-cell lysate from donors (MSD, > 19.6 days or > 19.1 days; mortality, 38% or 50%). The morbidity and mortality of mice exposed to a 1 LD50 of HSV were also increased when they were continuously treated with recombinant murine IL-4. However, the survival rate of mice exposed to a 10 LD50 of HSV increased after multiple treatments of these mice with anti-IL-4 monoclonal antibody. IL-4-producing cells were detected in a population of HSV-STC, and IL-4 was produced when these cells were cultured in the presence of UV-inactivated HSV in vitro. These results indicate that IL-4 plays an important role in the progression of acute HSV infection and, through the production of IL-4, HSV-STC may increase the severity of the acute-phase infection of HSV in mice.

Activation of CD4+ T cells in the presence of a nondepleting monoclonal antibody to CD4 induces a Th2-type response in vitro

In vitro experiments using purified rat CD4+ T cells in primary and secondary mixed leukocyte cultures (MLC) have been carried out to explore the mechanism of inhibition of cell-mediated autoimmune disease in the rat by a nondepleting monoclonal antibody (mAb) to CD4. Previous work has shown that W3/25, a mouse anti-rat CD4 mAb of immunoglobulin G1 isotype, completely prevents the development of the paralysis associated with experimental allergic encephalomyelitis (EAE) in Lewis rats, but does so without eliminating the encephalitogenic T cells. The in vitro experiments described in this study have shown that when CD4+ T cells were activated in the presence of the anti-CD4 mAb in a primary MLC, the synthesis of interferon (IFN) gamma, but not interleukin (IL) 2, was completely inhibited. After secondary stimulation, now in the absence of the mAb, the synthesis of IL-4 and IL-13 mRNA was greatly enhanced compared with that observed from CD4+ T cells derived from primary cultures in which the mAb was omitted. As IL-4 and IL-13 are known to antagonize cell-mediated immune reactions, and as EAE is cell-mediated disease, the data suggest that the W3/25 mAb controls EAE by modifying the cytokine repertoire of T cells that respond to the encephalitogen. The capacity for the mAb to suppress IFN-gamma synthesis provides, in part, an explanation for this change in cytokine production. These findings are discussed in terms of what is known of the factors that determine which cytokine genes are expressed on T cell activation. Possible implications for the evolution of T cell responses in human immunodeficiency virus infection are also discussed.

In vitro cytokine treatment of B cell defects in HIV-infected hemophilia patients

HIV-infected patients exhibit defects in B cell differentiation and in the IL-6 response of B cells, in association with autoantibody formation against T cells. These autoantibodies have been implicated as important factors in the development of immunodeficiency disease. As the restoration of defective B cell responses might prevent autoantibody formation and the resulting immunosuppression, we studied whether in vitro treatment with recombinant IL-2 (rIL-2), recombinant IL-4 (rIL-4) or recombinant IL-6 (rIL-6) might restore the response of B cells of HIV-infected patients. B cells of 6 HIV-negative hemophilia patients, 4 HIV-positive patients at CDC stage II, III, 4 HIV-positive patients at CDC stage IV, and 6 healthy controls were tested in Staphylococcus aureus Cowan I (SAC-I)-stimulated B cell cultures and Pokeweed mitogen (PWM)-stimulated allogeneic B and T cell cocultures. B cell differentiation was assessed in a reverse hemolytic plaque assay and by ELISA determination of IgM, IgG and IL-6 in culture supernatants. In vitro application of rIL-6 resulted in suppression of both elevated unstimulated and mitogen-stimulated B cell responses in a dose-dependent manner which was in part due to feedback inhibition. PWM- and SAC-I-stimulated IgG and IgM responses, respectively, could be restored after addition of 10 U/ml rIL-2 in HIV-negative patients, but not in HIV-positive patients. Addition of rIL-4 to cultures resulted in suppression of both unstimulated and mitogen-stimulated IL-6 secretion and B cell responses. Severely depressed B cell responses in CDC IV patients were not significantly affected by cytokine application. These results indicate that defective Ig responses in HIV-negative patients may be restored by rIL-2 treatment whereas HIV-induced B cell defects are not corrected by supply of T cell help or cytokines promoting B cell growth and differentiation.

T helper cell dichotomy to Candida albicans: implications for pathology, therapy, and vaccine design

Acquired immunity to Candida albicans is believed to prevent mucosal colonization of adult immunocompetent individuals from progressing to symptomatic infection. Resistance to disease appears to correlate with the detection of delayed-type hypersensitivity responses in vivo and a T helper type 1 (Th1) cytokine secretion profile in vitro. Cellular immunodeficiency, particularly HIV infection, greatly increases the risk of mucosal infection, confirming that CD(4+)-cell-directed immunity is effective locally in controlling infectivity of the yeast. While Th1-type CD4+ cell activation resulting in phagocyte-dependent immunity clearly represents an important mechanism of anticandidal resistance, clinical observations suggest that Th2-type CD4+ cell reactivity may be triggered by Candida antigens in several disease states, including symptomatic infections and immunopathology. This may imply that a Th1-type pattern of reactivity characterizes the saprophytic yeast carriage and resistance to disease by healthy humans, whereas Th2-type responses would be mostly associated with pathology. Moreover, Candida-specific T helper responses, namely humoral and cell-mediated immunity, appear to be reciprocally regulated, as typically occurs in experimental models of parasitic and retroviral infection, where the Th1/Th2 paradigm of acquired immunity has been best characterized. Recent studies, besides providing direct evidence for the occurrence of cross-regulatory Th1 and Th2 responses in mice with candidiasis, emphasize the potential of cytokine/anticytokine therapy for recruiting Candida-specific responses toward protective, Th1-type CD4+ cell reactivity. At the same time, these studies call attention to the possible consequences of C. albicans infection for immunopathology, allergy, and coinfection.

Hot water extracts of Chlorella vulgaris reduce opportunistic infection with Listeria monocytogenes in C57BL/6 mice infected with LP-BM5 murine leukemia viruses

The bacterial elimination after infection with Listeria monocytogenes was impaired in mice with murine acquired immunodeficiency syndrome (MAIDS) by infection with LP-BM5 murine leukemia virus. Oral administration of hot water extracts of Chlorella vulgaris (CVE) restored the capacity of MAIDS mice to eliminate L. monocytogenes in association with improvement of the deteriorated immune response to L. monocytogenes. DTH response to Listeria in CVE-treated MAIDS mice was significantly higher than that of MAIDS mice after Listeria infection in association with increases in number of CD4+CD8- and CD4-CD8+ alpha beta T-cells in the infected sites. CVE might be effective in the treatment of opportunistic infection in retrovirus-induced immunodeficient patients.

Administration of dehydroepiandrosterone reverses the immune suppression induced by high dose antigen in mice

Several factors including antigen concentration, the route of antigen administration, hormones and cytokines have shown to affect T cells to produce the distinct patterns of lymphokines which exert regulatory and effector functions of immune response. In this study, we asked whether administration of dehydroepiandrosterone (DHEA) to mice which were tolerized by high dose of antigen could modulate T cell functions to restore the suppressed cellular immune response and to produce the distinct lymphokines. An intravenous injection of high dose of sheep red blood cells induced suppression of delayed type hypersensitivity (DTH) and a single subcutaneous injection of the tolerant mice with DHEA restored the suppressed DTH response. Furthermore, in vitro treatment of spleen cells from tolerant mice with DHEA abolished the transfer of tolerance to naive recipients. Lymphocytes from the DHEA-treated tolerant mice produced more IFN-gamma and less IL-4 and IL-6 than the cells from tolerant animals without DHEA treatment. These findings indicate that DHEA could recover antigen-specific immune suppression by differentially affecting T cells to produce the distinct lymphokines.

Differential modulation of Th1- and Th2-related cytokine mRNA expression by a synthetic peptide homologous to a conserved domain within retroviral envelope protein

The influence of a synthetic retroviral peptide, CKS-17, on T helper type 1 (Th1)- or Th2-related cytokines was investigated in human blood mononuclear cells. Cells were stimulated with staphylococcal enterotoxin A, anti-CD3 plus anti-CD28 monoclonal antibodies, or lipopolysaccharide to induce cytokine mRNA. mRNA was detected by a reverse transcription-polymerase chain reaction or Northern blot analysis. CKS-17 down-regulated stimulant-induced mRNA accumulation for interferon gamma (IFN-gamma), interleukin (IL)-2, and p40 heavy and p35 light chains of IL-12, a cytokine that mediates development of Th1 response. CKS-17 up-regulated stimulant-induced mRNA accumulation of IL-10 and did not suppress Th2-related cytokine (IL-4, IL-5, IL-6, or IL-13) mRNA expression. A reverse sequence of CKS-17 peptide, used as a control, showed no such action. Anti-human IL-10 monoclonal antibody blocked ability of CKS-17 to inhibit mRNA accumulation for IFN-gamma but not the CKS-17 suppressive activity of IL-12 p40 heavy chain mRNA. Thus, CKS-17-mediated suppression of IFN-gamma mRNA expression is dependent upon augmentation of IL-10 production by CKS-17. This conserved component of several retroviral envelope proteins, CKS-17, may act as an immunomodulatory epitope responsible for cytokine dysregulation that leads to suppression of cellular immunity.

T cells expressing the gamma delta T cell receptor are not required for egg granuloma formation in schistosomiasis

Immunopathology in schistosomiasis consists of a granulomatous response around parasite eggs. It has been established that granuloma formation is mediated by CD4+ T helper cells. However, the role of T cells bearing the gamma delta T cell receptor (TCR) has not been determined. In this study we utilized mutant mice that lack either alpha beta or gamma delta T cells as a result of gene targeting to investigate the relative roles of alpha beta and gamma delta T cells in the induction of immunopathology related to schistosomiasis. Mutant and control mice were infected with Schistosoma mansoni and granuloma formation as well as lymph node cell proliferative responses to egg antigens were analyzed after 8 weeks. TCR delta mutant mice (lacking gamma delta T cells) displayed vigorous formation of egg granulomas that were not significantly different from those observed in normal controls, both in terms of granuloma size and cellular composition. In contrast, TCR alpha and TCR beta mutant mice (lacking alpha beta T cells) were unable to form granulomas. Moreover, mesenteric lymph node cells from TCR delta mutant and control mice responded strongly to egg antigens in vitro, while TCR alpha and beta mutant mice did not. Our studies show that in schistosomiasis granuloma formation and proliferative responses to egg antigens are strictly dependent on alpha beta T cells. They also suggest that gamma delta T cells by themselves can neither mediate a granulomatous inflammation, nor significantly modify one mediated by alpha beta T cells.

Immune complexes inhibit antimicrobial responses through interleukin-10 production. Effects in severe combined immunodeficient mice during Listeria infection

The presence of soluble antigen-antibody complexes renders mice highly susceptible to infection with the intracellular pathogen Listeria monocytogenes. In this report we show that this inhibition is manifest at the level of the innate immune response and is mediated by IL-10. Like immuno-competent mice, mice with the severe combined immunodeficient mutation (SCID) injected with immune complexes died from a sublethal dose of L. monocytogenes. These mice were protected if pretreated with neutralizing antibodies to IL-10. In vitro, immune complexes stimulated IL-10 production by SCID splenocytes and splenic macrophages. Likewise, immune complexes inhibited TNF and IFN-gamma production by SCID splenocytes cultured with heat-killed-L. monocytogenes. This inhibition was reversed by neutralization of IL-10 but not IL-4 or TGF-beta. Immune complexes and rIL-10 inhibited cytokine production by SCID splenocytes if added before or simultaneously with heat-killed-L. monocytogenes. These data support a model in which immune complexes modulate host defense and the immune response by stimulating the production of IL-10 from macrophages.

Immune Evasion by Babesia bovis and Plasmodium falciparum: Cliff-dwellers of the Parasite World

Erythrocyte-dwelling parasites, such as Babesia bovis and Plasmodium falciparum, are not accessible to the host immune system during most of their asexual reproductive cycle because they are intracellular. While intracellular, the host immune response must be directed toward the surface of the infected erythrocyte. Immune individuals mount protective antibody and cell-mediated responses which eliminate most of the parasites, yet some survive to establish chronic infections. In this review, David Allred discusses some of the mechanisms used by these parasites to evade individual immune mechanisms targeting the infected erythrocyte to survive in the hostile environment of an effective immune response.

Is alcohol consumption a cofactor in the development of acquired immunodeficiency syndrome?

Excessive alcohol (EtOH) consumption and acquired immunodeficiency syndrome (AIDS) are two major public health problems in the United States. Overwhelming evidence is showing that heavy EtOH ingestion broadly suppresses the various arms of immune response, seriously impairing the body's normal host defense to invading microbes and tumorigenesis. The onset of clinical symptoms of AIDS (low CD4+ T cells count, opportunistic infections, and tumors) is quite variable among HIV+ individuals with a mean incubation time 3-10 years following seroconversion. Because of the deleterious effects of chronic EtOH consumption on cytokine release, immune response, host defense, nutritional status, and oxidative stress, it has been believed to be a possible cofactor that could enhance the host's susceptibility to infections, and subsequently increase the rate of AIDS development. The purpose of this review is to present evidence indicating clinical disorders during EtOH ingestion in murine AIDS. These EtOH-induced abnormalities may promote a more rapid development of AIDS in HIV-infected individuals.