Role of cytokines in the differentiation of CD4+ T-cell subsets in vivo

Gamma interferon is critical for resistance to Theiler's virus-induced demyelination

Administration of neutralizing monoclonal antibody to gamma interferon increased Theiler's virus-induced demyelination and virus antigen persistence in the spinal cord in susceptible SJL/J mice and completely abrogated resistance such that all C57BL/10SNJ mice developed demyelination. These experiments support the hypothesis that gamma interferon is critically important for resistance to Theiler's virus-induced disease but is not required for myelin destruction.

Effect of bismuth salts on systemic and mucosal immune responses to orally administered cholera toxin

While the antimicrobial and antisecretory effects of bismuth salts are well documented, little is known regarding their effects on immune responses to enterotoxins such as that of V. cholerae or to orally administered vaccine antigens. To evaluate the effects of Pepto Bismol (PB) on the induction of systemic and mucosal immune responses to cholera toxin (CT), C57BL/6 mice were orally administered 10 micrograms CT and PB, or mice were pretreated with PB 30 min prior to CT administration. When co-administered with CT, PB attenuated serum IgG1, IgG2a, IgG2b and IgG3 anti-CT responses in a dose-dependent manner and also reduced levels of circulating anti-CT IgA and total serum IgE. Similarly, anti-CT intestinal IgA responses were also decreased. However, when administered 30 min prior to CT, PB had little to no effect on serum or intestinal anti-CT immunoglobulin responses. Administration of bismuth subsalicylate (BSS), the active component of PB, or sodium salicylate did not reduce immune responses to CT, suggesting that the combination of BSS plus other constituents contained within PB contributed to the decreased immune response to CT. Moreover, bismuth subgallate alone inhibited antibody responses to CT. Our data are consistent with the hypothesis that, when administered orally with CT, PB and bismuth subgallate create a physical barrier to antigen uptake.

Th1 and Th2 subsets: paradigms lost?

The T helper 1 (Th1)/Th2 model has provided a valuable framework to investigate and explain many immune reactions and now pervades current thinking on the regulatory role of T cells. However, individual T cells and clones display remarkable diversity in their cytokine profiles, collectively forming a continuous spectrum in which Th1 and Th2 cells may be only two of the possible extreme phenotypes. For these reasons, Anne Kelso argues that cytokine-producing T cells cannot be classified into discrete subsets.

Correlation of in vitro and in vivo effects of interferon-gamma with the spontaneous regression of a rat histiocytoma

Cytokines trigger activation of different lymphocyte populations, resulting in augmentation of humoral and cell-mediated immunity. We have examined the role of IFN-gamma in mediating AK-5 tumor regression. High levels of circulating IFN-gamma and IL-2 marked the process of regression. Moreover, interaction of immune NK cells with antibody-tagged AK-5 resulted in IFN-gamma secretion, providing in vitro evidence for the involvement of this cytokine. IFN-gamma and IL-2 potentiated the cytolytic activity of naive NK cells, suggesting their role in antitumor activity. Furthermore, pretreatment of immune NK cells with protein tyrosine kinase inhibitor downregulated the IFN-gamma release, suggesting that the secretion of IFN-gamma is phosphorylation dependent. Nonimmune cells could be induced to secrete IFN-gamma when exposed to rIL-12, demonstrating IL-12 dependence in inducing IFN-gamma release. In vivo administration of anti-IFN-gamma inhibited the cytotoxic activity and the process of tumor regression, further substantiating the role of IFN-gamma in regulating the rejection of AK-5 tumor. These observations suggest a definitive role for IFN-gamma in AK-5 regression. This cytokine in concert with IL-2 and IL-12 might aid in designing effective anticancer therapy.

Response of scid mice to establishment of Leishmania major infection

The initiation of Leishmania major infection in susceptible BALB/c mice is regulated by interferon-gamma (IFN-gamma). To examine further the mechanisms of IFN-gamma-dependent regulation of the establishment of L. major, we studied the characteristics of the infection in severe combined immunodeficient (scid) mice. In the first 2 weeks of infection, we observed a delay in the development of the lesions in the footpads and lower numbers of parasites in scid compared with BALB/c mice. By week 5 after infection, the size of the leishmanial lesion was similar in both strains of mice, but the number of parasites in scid mice was 100-fold higher than in BALB/c. Treatment with anti-IFN-gamma during the establishment of L. major did not alter the course of infection in scid mice, while it exacerbated lesion development in BALB/c mice. Macrophages from scid mice were unable to kill L. major when stimulated with IFN-gamma in vitro, and produced lower levels of nitric oxide compared with macrophages from susceptible BALB/c or the resistant C57Bl/6 mice. We examined whether delayed lesion development in scid mice was due to their inability to mount appropriate inflammatory responses. While significantly fewer nucleated cells were present in the footpads of scid mice compared with BALB/c, 2 and 3 weeks after infection, no difference in inflammatory response between scid and BALB/c mice was observed in response to L. major antigen in the footpads. In contrast, there was a dramatic increase in the number of cells in the popliteal lymph nodes of BALB/c mice. Decreased inflammatory responses of scid mice in the footpad (at the site of infection) may contribute to slower development of leishmanial lesions during the first 2 weeks of infection.

Tolerogenic forms of auto-antigens and cytokines in the induction of resistance to experimental allergic encephalomyelitis

Resistance to experimental allergic encephalomyelitis (EAE) induction by homogenized myelin (MSCH) in complete Freund's adjuvant (CFA) and pertussigen (P) in SJL mice was seen 1 week after intravenous injection of PLP 139-151 coupled to spleen cells (PLP-ECDI-SP). Although this resistance could be transferred by spleen cells enriched for CD8+ T cells and thus had a component of immunoregulatory T cells, it was primarily due to anergy, as it was reversible by four daily injections of interleukin (II)-2 starting 3 days after the PLP-ECDI-SP. Earlier treatment with IL-2 did not reverse the tolerance. In view of the known higher sensitivity to anergy induction of Th1 than of Th2 cells, a change in the cytokine balance in the response to MSCH+CFA after anergy induction might be responsible for the resistance to EAE induction. The effect of treatment with cytokines alone on induction of EAE was therefore also determined. Short-term (1-2 weeks) daily pretreatment with IL-2 (4000 U) or TGF-beta 2 (1 micrograms) somewhat decreased the susceptibility to subsequent EAE induction, but IL-4 (5 ng), IL-10 (5 micrograms) or IL-12 (50-200 ng) had no effect under those conditions, even if low doses of PLP were injected simultaneously. Daily injections of IL-4 over an 8-week period prior to immunization, however, significantly lowered the incidence of EAE. Simultaneous injections of IFN-gamma (2000 U/day) completely abolished this effect of IL-4. The effect of these cytokines administered immediately after the immunization with MSCH + CFA + P was also examined. As shown earlier, TGF-beta 2 (100-1000 ng/day) caused a marked protection when it was given intraperitoneally on days 5-9 after injection of MSCH + CFA. IL-4 (5 ng/day), in contrast, was very protective when administered on days 0-4 and less so when given on days 5-9 or even on days 0-12. IL-10 (1 microgram/day) was not protective under these conditions and IL-12 (50 ng/day) significantly increased the severity and mortality of EAE when given on days 0-4 after MSCH + CFA.

The influence of allo-class II MHC-specific Th2 cells on the generation of CD4 and CD8 cytotoxic T cells to associated class I and class II MHC alloantigen

There is considerable interest in whether CD4 T cell function can affect the outcome of allogeneic transplants. In mice tolerant to an isolated class II MHC disparity, the normal Th1 activity in vitro associated with graft rejection is switched to Th2 in tolerant animals. Because clinical transplants involve multiple class I and II MHC disparities we tested how the switch to Th2 activity of tolerant mice would affect the generation of CD4 and CD8 cytotoxic T cells (CTL) against MHC alloantigens to which the mice were not tolerant. A.TH mice (KkIsDd) were rendered neonatally tolerant of A.TL (KkIkDd) and the generation of CD4 or CD8 CTL measured in a mixed lymphocyte reaction (MLR) against (A.TL x B6)F1 stimulators. Normal mice generated CD4 CTL against both A.TL and B6 (KbIbDb), but tolerant mice were unable to generate cytotoxicity against either A.TL or B6. However, tolerant cells were able to generate CD8 CTL against B6. IL-4 inhibited the generation of CD4, but not CD8, CTL by normal cells and anti-IL-4 antibody was shown to increase the generation of CD4 CTL against B6 in F1 stimulated cultures. Overall the results showed that a Th2 response could inhibit the generation of CD4 CTL against concomitant alloantigen in a process at least partially involving IL-4, but that, conversely, tolerant Th2 cells could help in the generation of CD8 CTL. The results suggest that with whole MHC disparities a simple change of CD4 T cells to Th2 would not be enough to procure graft acceptance.

Cytokines as adjuvants in immunocompromised hosts

Vaccination of immunocompromised subjects may be ineffective due to the poor immune responses induced. In addition, vaccination with live attenuated organisms may also be dangerous due to the possible lack of control of the infection. This review describes the protection of cytokines in the vaccination of immunocompromised individuals. Cytokines have possible roles as immunological adjuvants, enhancing immune responses to vaccination, and can also have effects on the growth of live vaccines or vaccine vectors.

Contribution of alpha/beta and gamma/delta T lymphocytes to immunity against Mycobacterium bovis bacillus Calmette Guérin: studies with T cell receptor-deficient mutant mice

Mutant mice with defined T cell deficiencies were infected with Mycobacterium bovis bacillus Calmette Guérin (BCG) and the relative contribution of alpha/beta T cells and gamma/delta T cells to the host immune response was assessed. Recombinase activating gene (RAG-1)-/- mutants as well as T cell receptor (TcR) beta-/-, but not TcR-delta-/-, mutants succumbed to M. bovis BCG infection and failed to develop granulomatous lesions. Antigen-induced IFN-gamma production by spleen cells in vitro was abrogated in RAG-1-/- mutants and markedly diminished in TcR-beta-/- and TcR-delta-/- mice. Reconstitution experiments suggest that both alpha/beta and gamma/delta T cells are essential for antigen-specific IFN-gamma secretion. Our data formally prove the crucial role of alpha/beta T cells and reveal accessory functions of gamma/delta T cells in optimum immunity against M. bovis BCG.

Effect of granulocyte-macrophage colony-stimulating factor in experimental visceral leishmaniasis

GM-CSF induces three effects potentially beneficial in visceral leishmaniasis: blood monocyte mobilization, macrophage activation, and amelioration of granulocytopenia. To determine the experimental role and effect of GM-CSF in this intracellular infection, livers from Leishmania donovani-infected BALB/c mice were tested for GM-CSF mRNA expression and mice were treated with anti-GM-CSF antiserum or GM-CSF. L. donovani infection upregulated hepatic GM-CSF mRNA expression by 10-fold, and anti-GM-CSF treatment exacerbated visceral infection and tripled liver parasite burdens 4 wk after challenge. In euthymic mice with established infection, treatment with 1-5 micrograms/d murine GM-CSF induced three dose-related effects: peripheral blood leukocytosis, preferential accumulation of myelomonocytic cells at visceral foci of infection, and leishmanicidal activity comparable to that achieved by IFN-gamma. These effects were either largely or entirely T cell dependent. Treatment with human GM-CSF also induced anti-leishmanial activity but with little effect on peripheral leukocyte number or tissue myelomonocytic cell influx; human G-CSF stimulated marked peripheral granulocytosis and neutrophil tissue accumulation but induced little antileishmanial effect. These results identify a role for endogenous GM-CSF in the initial host defense response to L. donovani, reemphasize the influxing monocyte as an effector cell, and indicate that GM-CSF can be used as an antileishmanial treatment.

T cell and non-T cell compartments can independently determine resistance to Leishmania major

In experimental murine cutaneous leishmaniasis caused by Leishmania major (Lm), the cellular determinants governing development of protective or exacerbative T cells are not well understood. We, therefore, attempted to determine the influence of T cell and non-T cell compartments on disease outcome. To this end, T cell chimeric mice were constructed using adult thymectomized lethally irradiated, bone marrow-reconstituted (ATXBM) animals of genetically resistant, C57BL/6, or susceptible, BALB/c, backgrounds. These hosts were engrafted with naive T cell populations from H-2-congenic susceptible, BALB.B6-H-2b, or resistant, C57BL/6.C-H-2d, animals, respectively. Chimeric mice were then infected with Lm, and disease outcome was monitored. BALB/c T cell chimeric mice, BALB/c ATXBM hosts given naive C57BL/6.C-H-2d T cells, resolved their infections as indicated by reductions in both lesion size and parasite numbers. Furthermore, the mice developed typical Th1 (interferon[IFN]-gamma hiinterleukin[IL]-4lo) cytokine patterns. In contrast, both sham chimeric, BALB/c ATXBM hosts given naive BALB/c T cells, and control irradiated euthymic mice succumbed to infection, producing Th2 profiles (IFN-gamma loIL-4hiIL-10hi). C57BL/6 T cell chimeras, C57BL/6 ATXBM hosts given naive BALB.B6-H-2b T cells, resolved their infections as did C57BL/6 sham chimeras and euthymic controls. Interestingly, whereas C57BL/6 control animals produced Th1 cytokines, chimeric animals progressed from Th0 (IFN-gamma hiIL-4hiIL-10hi) to Th2 (IFN-gamma loIL-4hiIL-10hi) cytokine profiles as cure ensued. Both reconstitution and chimeric status of all mice were confirmed by flow cytometry. In addition, T cell receptor V beta usage of Lm-specific blasts was determined. In all cases, V beta use was multiclonal, involving primarily V beta 2, 4, 6, 8.1, 8.2, 8.3, 10, and 14, with relative V beta frequencies differing between H-2b and H-2d animals. Most importantly, however, these differences did not segregate between cure and noncure outcomes. These findings indicate that: (a) genetic traits determining cure in Lm infection can direct disease outcome from both T cell and non-T cell compartments; (b) the presence of the curing genotype in only one compartment is sufficient to confer cure; (c) curing genotype T cells autonomously assume a Th1 cytokine profile-mediating cure; (d) noncuring genotype T cells can mediate cure in a curing environment, despite the onset of Th2 cytokine production; and lastly, (e) antigen specificity of responding T cells, as assessed by V beta T cell receptor diversity, is not a critical determinant of disease outcome.

Interleukin-12 profoundly up-regulates the synthesis of antigen-specific complement-fixing IgG2a, IgG2b and IgG3 antibody subclasses in vivo

The influence of the cytokine interleukin-12 (IL-12) on humoral immune responses was studied in vivo. CBA/J mice immunized with protein antigens (keyhole limpet hemocyanin, phospholipase A2) adsorbed to aluminum hydroxide (Alum) develop a Th2-like immune response characterized by the production of large amounts of IgG1 as well as some IgE but little IgG2a, IgG2b and IgG3 antibodies. IL-12 is a cytokine that promotes the development and the activation of Th1 cells. Th1 cells are involved in the induction of cellular immunity, which is characterized by low or absent antibody production. On the other hand, some Th1-like immune responses are associated with a strong antibody production of the IgG2a, IgG2b and IgG3 subclasses. Thus, we investigated whether treatment with IL-12 would down-regulate the humoral immune response or stimulate antibody production of the IgG2a, IgG2b and IgG3 subclasses. We observed that: 1) administration of IL-12 to mice together with protein antigens adsorbed to Alum strongly enhanced the humoral immune response by increasing the synthesis of antigen-specific antibodies of the IgG2a, IgG2b and IgG3 subclasses 10- to 1000-fold. The synthesis of IgG1 was not or only slightly (2-5-fold) enhanced, whereas that of the IgE isotype was suppressed. 2) These effects of IL-12 were observed when high (10 micrograms, 100 micrograms) or low doses (0.1 microgram) of antigen were used for immunization. 3) Titration of IL-12 in vitro revealed that IgG2a is strongly up-regulated over a wide dose range of IL-12 (10 to 1000 ng/day). 4) The effects of IL-12 in vivo are at least partially interferon (IFN)-gamma-dependent because an anti-IFN-gamma mAb in combination with IL-12 prevented most of the enhanced IgG2a production. 5) Mice receiving IL-12 showed a strong up-regulation of IFN-gamma but no inhibition of IL-5 synthesis by spleen cells activated ex vivo with antigen. These results suggest that IL-12 is a potent adjuvant for enhancing humoral immunity to protein antigens adsorbed to Alum, primarily by inducing the synthesis of the complement-fixing IgG subclasses 2a, 2b and 3.

Cytokine expression in the liver during the early phase of murine tularemia

Cytokine expression was determined in the livers of mice inoculated subcutaneously with Francisella tularensis LVS. During the first 48 h of infection, there was a logarithmic increase of bacteria in the liver, with a doubling time of 2.5 h. Within 48 h, tumor necrosis factor alpha (TNF-alpha), interleukin 10 (IL-10), IL-12, and gamma interferon (IFN-gamma) mRNAs were expressed, and production of TNF-alpha and IFN-gamma was demonstrated. There was no expression within 96 h of mRNA from IL-2, IL-3, or IL-4. After subcutaneous inoculation of heat-killed LVS, no expression of any of the cytokine mRNAs and no increase in the levels of TNF-alpha or IFN-gamma occurred. The expression of TNF-alpha, IL-12, and IFN-gamma is held to be important to evoke an early T-cell-independent host defense against F. tularensis as well as to drive the expansion of a protective Th1 cell response.

Immunoglobulin isotype modulation after administration of IL-12

We have begun a series of experiments assessing the role of IL-12 in the humoral immune response. IL-12 is known to enhance cellular immunity causing a shift toward a Th1, as opposed to a Th2, response. IL-12 is also a potent stimulator of IFN-gamma production which, among other activities, modulates isotype expression particularly with respect to IgG2a. We have performed a series of experiments involving the concurrent dosing of mice with murine IL-12 and TNP-KLH followed by the monitoring of IgG1 and IgG2a anti-TNP responses and total IgG1 and IgG2a levels. Following administration of IL-12, specific anti-TNP titers showed an IgG2a increase while IgG1 responses were markedly lower than those exhibited by animals which did not receive IL-12. Total IgG1 levels in IL-12 treated mice remained at or near baseline while untreated mice demonstrated an increase in total IgG1 levels. In addition, lymph nodes from these mice were removed, stimulated with KLH and assayed for expression of murine IFN-gamma and IL-4. Murine IFN-gamma levels in supernatants obtained from IL-12 treated mice were elevated over those seen in untreated mice while IL-4 levels were suppressed.

Interferon gamma-independent effects of interleukin 12 administered during acute or established infection due to Leishmania major

Interleukin 12 (IL-12) is a powerful stimulus for the growth of activated T and natural killer cells, their generation of interferon gamma (IFN-gamma), and the differentiation of T helper type 1 (Th1) effector cells from naive precursors in vitro. These activities are consistent with the capacity of exogenous IL-12 to heal otherwise susceptible BALB/c mice infected with the intramacrophage parasite Leishmania major. Using this characterized model of CD4 cell subset differentiation, we examined the immunologic effects of IL-12 administered either at the time of infection, when naive T cells are primed, or after 14 days of infection, by which time CD4+ subset differentiation has occurred. Given with the inoculation of parasites, IL-12 induced IFN-gamma and IL-10 and markedly suppressed IL-4. Effects on IL-10 and IL-4 were comparable in mice with homozygous disruption of the IFN-gamma gene (IFN-gamma 0/0), and suppression of IL-4 was unchanged by administration of neutralizing anti-IL-10 antibody. Induction of IFN-gamma and IL-10 mRNA by IL-12 also occurred in infected SCID mice. Given after day 14 of infection, however, IL-12 not only induced IFN-gamma and IL-10 but also induced IL-4 in normal and IFN-gamma 0/0 mice. These data demonstrate direct effects of IL-12 independent of IFN-gamma, IL-10, and IL-4 and demonstrate that the ineffectiveness of IL-12 administered following infection with L. major correlates with resistance of differentiated Th2 cells to the IL-4-suppressing activity of IL-12.

From AIDS to parasite infection: pathogen-mediated subversion of programmed cell death as a mechanism for immune dysregulation

Premature cell death can result either from cell injury or degeneration, leading to necrosis, or from the activation of a physiological cell-suicide process, termed programmed cell death or apoptosis, that is regulated by intercellular signalling. This process plays an essential role in the selection of developing lymphocytes, and is also involved in the function of the mature adaptative immune system. A growing number of experimental findings during the last 4 years has provided support to our hypothesis that inappropriate HIV-mediated dysregulation of programmed T-cell death is relevant to AIDS pathogenesis. A series of recent experimental results also supports the general concept that the persistence and pathogenesis of several infectious pathogens, ranging from retroviruses to parasites, may be related to their capacity to dysregulate programmed cell death in various cell populations including lymphocytes. Subversion by pathogens of the physiological control of programmed cell death provides a paradigm for the pathogenesis of a wide range of infectious diseases that involve immune dysregulation and suggests therapeutic potential for the in vivo modulation of cell signalling.

Depletion of interleukin-4 in BALB/c mice with established Leishmania major infections increases the efficacy of antimony therapy and promotes Th1-like responses

Whereas most inbred mouse strains mount a protective Th1 helper T-cell response following infection with Leishmania major, an ineffective Th2 response develops in BALB/c mice, leading to the development of disseminated, ultimately fatal disease. Interleukin-4 (IL-4) production is required for the initiation of the Th2 response, though little is known about the requirements for the long-term maintenance of this response. In order to investigate the role of the expanding parasite population on the Th2 response, mice infected for 2 weeks with L. major, which exhibited a Th2-like cytokine profile, were treated with a leishmanicidal agent (Pentostam) and/or various doses of anti-IL-4 antibody. Untreated mice, mice treated with Pentostam alone, or mice treated with 2.5 mg of anti-IL-4 antibody given at days 13 and 21 of infection developed progressive disease. However, in 8 of 10 mice treated with this dose of anti-IL-4 antibody plus Pentostam lesion development was arrested and lesions were either controlled or eventually healed. Healing was associated with the production of high levels of gamma interferon by spleen cells, and low levels of immunoglobulin E in serum compared with levels for control animals, indicating that a Th1-like response had developed in mice receiving both treatments. Thus, depletion of IL-4 only in combination with a reduction in the parasite burden allowed the expression of a Th1 response. When the dose of anti-IL-4 antibody was increased to 5 mg per injection, all mice treated with this dose of antibody, with or without Pentostam therapy, healed. However, combined therapy with Pentostam in mice treated with this dose of antibody had an additional protective effect. As expected, a Th1 response developed in mice treated with this dose of anti-IL-4 antibody with or without combined therapy with Pentostam, whereas a Th2 response developed in control mice. Thus, a significant effect on the course of disease is noted when mice with established L. major infections are treated with anti-IL-4 antibody in combination with Pentostam, suggesting that the combined effect of inhibiting IL-4 and reducing the parasite burden has a dramatic effect on the development of resistance to L. major.

Horizons in pharmacologic intervention in allergic contact dermatitis

The treatment of allergic contact dermatitis remains a major challenge. Current management strategies consist of elimination of the allergen when possible and therapy for symptoms with topical or systemic corticosteroids. With increasing exposure of the human skin to environmental antigens and haptens, more selective treatment options are needed. Advances in the elucidation of the skin immune system and of the cellular and molecular events in immunologic processes may allow targeted methods of controlling delayed hypersensitivity reactions. This review focuses on mechanisms of established therapeutic agents and new developments, such as FK 506 (tacrolimus), pentoxifylline, and vitamin D3 derivative, for suppression of any phase of allergic contact dermatitis.

Interferon-gamma and host antimicrobial defense: current and future clinical applications

In the 1980s, substantive experimental data and emerging clinical results suggested that interferon-gamma (IFN-gamma), a T-cell-derived lymphokine with broad macrophage-activating effects, had considerable potential in the treatment of nonviral infections as a host defense-enhancing antimicrobial agent. During the past 6 years, the breadth of the experimental activity with IFN-gamma against nonviral pathogens has been expanded still further, and pilot studies and formal clinical trials using IFN-gamma have been undertaken in the treatment of patients both at risk for and with active infections. Thus far, IFN-gamma has been approved for use as prophylaxis in patients with chronic granulomatous disease. However, IFN-gamma also appears effective as adjunctive therapy for at least one disseminated intracellular infection (visceral leishmaniasis), and in conjunction with conventional therapy, may benefit patients with certain forms of cutaneous leishmaniasis, disseminated Mycobacterium avium complex infection, and lepromatous leprosy. Despite a rationale for its use, IFN-gamma has not yet been tested in tuberculosis or fungal or common bacterial infections nor sufficiently examined in the prevention and/or treatment of the opportunistic infections related to acquired immunodeficiency syndrome. IFN-gamma remains a promising host defense-enhancing cytokine with still unexplored clinical potential.

Cytokines and regulation of allergic sensitization to chemicals

Sensitization to chemicals and the elicitation of allergic reactions results from the stimulation of specific immune responses. Adaptive immunity is orchestrated by cytokines, a family of inducible glycoproteins that influence in many ways the behaviour of, and interaction between, cells which mediate immune and inflammatory responses. In this article the role of cytokines in the development of cutaneous immune responses to chemical allergens and in directing the quality of immune responses provoked by such materials is discussed.

Cytokines and T cell switching

In recent years, the phenotypic characterization of T cell subsets has given way to a functional dichotomy based essentially on their cytokine profiles. In this context, the CD4+ helper T cell subset has been shown to consist of two types, termed Th1 and Th2. In general, Th1 cells produce interleukin (IL)-2 and interferon (IFN)-gamma, while Th2 cells characteristically produce IL-4, IL-5, and IL-6. The major function of the Th1 subset is to mediate delayed-type hypersensitivity reactions and their secondary function is suppression of B cell activity. In contrast, the major function of the Th2 subset is to provide B cell help, while their secondary function is cell-mediated immune suppression. A similar dichotomy has also been described for CD8+ T cells. The role that these functional T cell subsets and their cytokines play in terms of their protective and nonprotective outcomes in a variety of infectious and oral diseases is reviewed.

Mucosal immunity to infection with implications for vaccine development

The induction of effective mucosal immunity that also provides systemic immunity is a considerable challenge. Over the past two years, efforts to develop novel mucosal vaccine delivery systems to induce mucosal immunity against bacterial and viral diseases, including HIV, have dramatically increased. Here we cite novel vaccines and delivery systems being used to establish effective mucosal immunity.

Cloning and expression of the cervine interleukin 4 gene

Interleukin 4 (IL-4), a cytokine produced by the T helper 2 subset of T lymphocytes is involved in up regulating antibody responses. A source of recombinant cervine IL-4 would be useful for studying the immune response of deer to tuberculosis. We report here the cloning, sequencing and expression of recombinant cervine IL-4. To achieve this mRNA was isolated from red deer (Cervus elaphus) mononuclear leucocytes. First strand cDNA was synthesized from the mRNA and the IL-4 cDNA was amplified, cloned and sequenced. The IL-4 cDNA is 408 bp in length and the deduced amino acid sequence is 92% homologous with the published bovine IL-4 amino acid sequence. IL-4 was expressed using the baculovirus expression system in Spodoptera frugiperda Sf9 cells. Northern blot, SDS-PAGE analysis and bioassay were used to confirm the expression of IL-4.

Interleukin-12 but not interferon-gamma production correlates with induction of T helper type-1 phenotype in murine candidiasis

By means of polymerase chain reaction-assisted mRNA amplification, we have monitored message levels of interleukin (IL)-12 in splenic macrophages and of interferon-gamma (IFN-gamma), IL-4, and IL-10 in CD4+ and CD8+ T cells using Candida albicans/host combinations that result either in a T helper type-1 (Th1)-associated self-limiting infection ("healer mice") or in a Th2-associated progressive disease ("nonhealer mice"). The timing and pattern of message detection did not differ qualitatively by the expression of IFN-gamma or IL-10 mRNA in CD4+ and CD8+ cells from healer (i.e. PCA-2 into CD2F1) vs. nonhealer (i.e. CA-6 into CD2F1 or PCA-2 into DBA/2) mice. In contrast, IL-4 mRNA was uniquely expressed by CD4+ cells from nonhealer animals. IL-12p40 was readily detected in macrophages from healer mice but was detected only early in infection in mice with progressive disease. Cytokine levels were measured in sera, and antigen-driven cytokine production by CD4+ and CD8+ cells was assessed in vitro, while IFN-gamma-producing cells were enumerated in CD4- CD8- cell fractions. Overall, our results showed that (i) antigen-specific secretion of IFN-gamma protein in vitro by CD4+ cells occurred only in healing infection; (ii) IL-4- and IL-10-producing CD4+ cells would expand in nonhealer mice in the face of high levels of circulating IFN-gamma, likely released by CD4- CD8- lymphocytes; (iii) a finely regulated IFN-gamma production correlated in the healer mice with IL-12 mRNA detection, and IL-12 was required in vitro for yeast-induced development of IFN-gamma-producing CD4+ cells. Although the mutually exclusive production of IL-4/IL-10 and IFN-gamma by early CD4+ cells may be the major discriminative factor of cure and noncure responses in candidiasis, IL-12 rather than IFN-gamma production may be an indicator of Th1 differentiation.

T helper type 1 development of naive CD4+ T cells requires the coordinate action of interleukin-12 and interferon-gamma and is inhibited by transforming growth factor-beta

It was observed in vitro and in vivo that both interferon (IFN)-gamma and interleukin (IL)-12 can promote the development of T helper type 1 (TH1) cells. Since IL-12 was shown to be a costimulator for the production of IFN-gamma by T or natural killer (NK) cells, IL-12 might play only an indirect role in TH1 differentiation by providing IFN-gamma which represents the essential differentiation factor. Using anti-CD3 monoclonal antibody (mAb) for activation of naive CD4+ T cells in the absence of accessory cells we could demonstrate that costimulation by IFN-gamma alone results only in marginal TH1 development. Similarly, IL-12 in the absence of IFN-gamma is only a poor costimulator for inducing differentiation towards the TH1 phenotype. Our data indicate that both cytokines are required to allow optimal TH1 development and that IL-12 has a dual role, it promotes differentiation by direct costimulation of the T cells and also enhances the production of IFN-gamma which serves as a second costimulator by an autocrine mechanism. Another cytokine that was reported to favor TH1 differentiation in certain experimental systems is transforming growth factor (TGF)-beta. With naive CD4+ T cells employed in this study TGF-beta strongly inhibited the production of IFN-gamma triggered by IL-12 as well as the IL-12-induced TH1 development. When TGF-beta was combined with anti-IFN-gamma mAb for neutralization of endogenous IFN-gamma the TH1-inducing capacity of IL-12 was completely suppressed.

CD4pos, NK1.1pos T cells promptly produce interleukin 4 in response to in vivo challenge with anti-CD3

Injection of anti-CD3 antibodies causes prompt expression of interleukin (IL)-4, IL-2, and interferon gamma (IFN-gamma) mRNA among spleen cells. The optimal dose of anti-CD3 for such induction was 1.33 microgram/animal; lymphokine mRNA was first observed at 30 min, peaked at 90 min, and was undetectable (for IL-4) or had declined markedly by 4 h. Cells harvested from spleens of mice injected with anti-CD3 90 min earlier secreted IL-4, IL-2, and IFN-gamma without further stimulation. By contrast, in vitro stimulation with anti-CD3 of spleen cell suspensions or splenic fragments from noninjected donors failed to cause prompt production of IL-4 and, even after 24 h of stimulation, the amount of IL-4 produced in such cells was substantially less than that secreted within 1 h by spleen cell suspensions or splenic fragments from mice injected with anti-CD3 90 min earlier. Production of IL-4 by spleen cells from anti-CD3-injected mice was not inhibited by pretreatment with anti-IL-4 antibody or with IFN-gamma or tumor growth factor beta nor enhanced by treatment with IL-4. By contrast, CTLA-4 immunoglobulin (Ig) treatment clearly diminished IL-4 production in response to in vivo anti-CD3, indicating that cellular interactions involving CD28 (or related molecules) were important in stimulation. Cell sorting analysis indicated that the cells that produced IL-4 in response to in vivo injection of anti-CD3 were highly enriched in CD4pos cells with the phenotype leukocyte cell adhesion molecule-1 (LECAM-1)dull, CD44bright, CD45RBdull, NK1.1pos. Indeed, the small population of CD4pos, NK1.1pos cells had the great majority of the IL-4-producing activity of this population. Injection with Staphylococcal enterotoxin B also caused prompt induction of IL-4 mRNA; the cells that were principally responsible for production also had the phenotype of CD4pos, NK1.1pos. These results suggest that possibility that this rare population of T cells may be capable of secreting IL-4 at the outset of immune responses and thus may act to regulate the pattern of priming of naive T cells, by providing a source of IL-4 to favor the development of T cell helper 2-like IL-4-producing cells.

Differential effects of interleukin-12 on the development of naive mouse CD4+ T cells

The influence of interleukin (IL)-12 and IL-4 on the differentiation of naive CD4+ T cells was studied in an accessory cell-free in vitro system. Dense CD4+ T cells were purified from unimmunized mice and activated using immobilized anti-CD3 monoclonal antibodies (mAb) in the presence of IL-4, IL-12, or a combination of both cytokines, and restimulated after 6 days by re-exposure to anti-CD3-coated culture wells. T cells initially activated in the presence of IL-4 produced substantial amounts of IL-4 and trace amounts of interferon (IFN)-gamma after restimulation at day 6 with plate-bound anti-CD3 mAb. By contrast, T cells primed in the presence of IL-12 produced high levels of IFN-gamma and only minimal amounts of IL-4, thus indicating that IL-12 and IL-4 by acting directly on stimulated naive CD4+ T cells support the development of TH1 and TH2 cells, respectively. When naive CD4+ T cells were stimulated in the presence of IL-12 together with IL-4 in comparable concentrations, the effect of IL-12 on TH1 differentiation was largely inhibited by IL-4. On the other hand, IL-12 exerted no inhibitory effect on IL-4-induced TH2 differentiation but rather enhanced the production of IL-4 after restimulation of the respective T cells. Decreasing amounts of IL-4 in combination with a high level of IL-12 led to an increasing production of IFN-gamma by the emerging T cells and, simultaneously, to a relatively high production of IL-4. These data were confirmed by time-course experiments which revealed that the delayed addition of IL-4 to IL-12-primed T cell cultures resulted in a gradual restoration of IFN-gamma production whereas in parallel the secretion of IL-4 was not reduced over a wide period of delay (6-72 h). These results, therefore, demonstrate that (a) IL-4 dominates the effect of IL-12, (b) IL-12 promotes the development of TH1 cells; however, in the presence of IL-12 and relatively high levels of IL-4 also the development of TH2-like cells is slightly but significantly enhanced by IL-12, and (c) high amounts of IL-12 in combination with relatively low levels of IL-4 give rise to a T cell population that upon rechallenge exhibited a cytokine profile resembling that of TH0 cells.

Regulatory interactions between CD45RBhigh and CD45RBlow CD4+ T cells are important for the balance between protective and pathogenic cell-mediated immunity

BALB/c mice infected with the intracellular protozoan Leishmania major mount a T helper cell 2 (Th2) response that fails to control growth of the parasite and results in the development of visceral leishmaniasis. Separation of CD4+ T cells into CD45RBhigh and CD45RBlow subsets showed that the L. major-specific Th2 cells were contained within the CD45RBlow population as these cells produced high levels of antigen-specific interleukin 4 (IL-4) in vitro and transferred a nonhealing response to L. major-infected C.B-17 scid mice. In contrast, the CD45RBhighCD4+ population contained L. major-reactive cells that produced interferon gamma (IFN-gamma) in vitro and transferred a healing Th1 response to L. major-infected C.B-17 scid mice. Transfer of the Th1 response by the CD45RBhigh population was inhibited by the CD45RBlow population by a mechanism that was dependent on IL-4. These data indicate that L. major-specific Th1 cells do develop in BALB/c mice, but their functional expression is actively inhibited by production of IL-4 by Th2 cells. In this response, the suppressed Th1 cells can be phenotypically distinguished from the suppressive Th2 cells by the level of expression of CD45RB. Although the CD45RBhigh population mediated a protective response to L. major, C.B-17 scid mice restored with this population developed a severe inflammatory response in the colon that was independent of L. major infection, and was prevented by cotransfer of the CD45RBlow population. The colitis appeared to be due to a dysregulated Th1 response as anti-IFN-gamma, but not anti-IL-4, prevented it. Taken together, the data show that the CD4+ T cell population identified by high level expression of the CD45RB antigen contains cells that mediate both protective and pathogenic Th1 responses and that the reciprocal CD45RBlow population can suppress both of these responses. Whether suppression of cell-mediated immunity is beneficial or not depends on the nature of the stimulus, being deleterious during L. major infection but crucial for control of potentially pathogenic inflammatory responses developing in the gut.

Endogenous IL-10 and IFN-gamma production controls thymic cell proliferation in mice acutely infected by Trypanosoma cruzi

Thymocytes from mice with experimental Trypanosoma cruzi infection respond poorly to Con-A stimulation. However, the proliferative capacity of these cells is not impaired, as demonstrated by the fact that at high doses, exogenous rIL-2 restores thymidine uptake. This finding could be explained either by insufficient IL-2 production or by the appearance of inhibitory factors during T. cruzi infection. This paper shows that in response to Con A, IL-2 production is decreased in the model. Furthermore, the whole profile of cytokine production is modified, with a striking increase in IL-10, IFN-gamma, IL-4, IL-5 and IL-6 production. The results indicate that IL-10 plus IFN-gamma are responsible for the decrease in the Con A-induced proliferation since a normal proliferative response as well as normal IL-2 production can be restored if both cytokines are neutralized by adding their monoclonal antibodies (MoAbs). Evidence is provided also for an enhanced non-specific cytotoxicity of thymic cells from infected mice that might involve IL-4, IL-5 and IL-6. This is the first study demonstrating an alteration of thymic cell function by T. cruzi infection which results from overstimulation of IL-10 and IFN-gamma production.

Commitment to lymphokine profile during primary in vitro stimulation

We have shown previously that different conditions in primary in vitro SEB stimulation of resting CD4+ T cells, could induce selectively production of either IFN gamma or IL4 and IL10. The present investigation shows that the priming conditions also decide which lymphokines will be produced during restimulations. The cells that had been induced to produce mainly IFN gamma during the primary SEB stimulation, or during stimulation with IL4 and IL10, synthesized the same lymphokines at restimulation, regardless of stimuli and were unaffected by exogenous IL4. Thus, at an early stage of primary SEB stimulation, cells became committed to produce a certain pattern of lymphokines which remained throughout the period of in vitro culture testing.

Antigen-presenting human T cells and antigen-presenting B cells induce a similar cytokine profile in specific T cell clones

One of the factors that may influence the cytokine secretion profile of a T cell is the antigen-presenting cell (APC). Since activated human T cells have been described to express major histocompatibility complex (MHC) class II molecules as well as costimulatory molecules for T cell activation, like e.g. ICAM-1, LFA-3 and B7, they might play a role as APC and be involved in the regulation of T-Tcell interactions. To define further the role of T cells as APC we tested their capacity to induce proliferation and cytokine production in peptide- or allospecific T cell clones and compared it with conventional APC, like B lymphoblasts (B-LCL) or HTLV-1-transformed T cells, or with non-classical APC, like activated keratinocytes or eosinophils. CD4+, DP-restricted T cell clones specific for a tetanus toxin peptide (amino acids 947-967) and CD4+, DR-restricted allospecific T cell clones produced interleukin (IL)-2, IL-4, tumor necrosis factor-alpha and interferon-gamma (IFN-gamma) after phorbol 12-myristate 13-acetate and ionomycin stimulation and a more restricted cytokine pattern after antigen stimulation. Dose-response curves revealed that the antigen-presenting capacity of activated, MHC class II+, B7+ T cells was comparable to the one of B-LCL. Both APC induced the same cytokine profile in the T cell clones despite a weaker proliferative response with T cells as APC. Suboptimal stimulations resulted in a lower IFN-gamma/IL-4 ratio. Cytokine-treated, MHC class II+ keratinocytes and eosinophils differed in the expression of adhesion molecules and their capacity to restimulate T cell clones. The strongly ICAM-1-positive keratinocytes induced rather high cytokine levels. In contrast, eosinophils, which express only low densities of MHC class II and no or only low levels of adhesion molecules (B7, ICAM-1 and LFA3), provided a reduced signal resulting in a diminished IFN-gamma/IL-4 ratio. We conclude that non-classical APC differ in their capacity to restimulate T cell clones, whereby the intensity of MHC class II and adhesion molecules (B7, ICAM-1) expressed seems to determine the efficacy of this presentation.

Interferon-gamma and interleukin-4 in human Leishmania donovani infections

Clinical and immunological similarities between Leishmania donovani infections in humans and L. major infections in mice suggest that some of the pathophysiological mechanisms are the same in the two conditions. Both infections can result either in a fatal systemic disease or in a self-limiting infection with few and mild symptoms. In the murine model the outcome of the infection is critically related to the cytokines produced by T lymphocytes activated by leishmanial antigens. Activation of the IFN-gamma producing Th1 subset of CD4 positive T cells results in cure and survival, whereas activation of the IL-4 secreting Th2 subset results in a progressive disease with fatal outcome. A similar Th1/Th2 dichotomy in the cytokine response to L. donovani may exist in humans, and may have influence on the outcome of infection. In murine leishmaniasis the levels of IL-4 and IFN-gamma at the time of infection can direct the T cell response into Th1 or Th2 type. If similar mechanisms operate in humans, the outcome of L. donovani infections may depend on the local cytokine environment in which early activation of Leishmania specific T cells takes place. Cytokines secreted by cross-reactive memory T cells, activated by antigens from the invading micro-organism, may contribute to determine this environment.

Differential regulation of IL-9-expression after infection with Leishmania major in susceptible and resistant mice

IL-9 is a pleiotropic lymphokine, one of its activities being the growth stimulation of certain CD4+ T lymphocytes. In murine cutaneous leishmaniasis, depending on the genetic background of the host mouse strain, vigorous proliferation of either mainly Th1 in resistant C57BL/6 mice or Th2-type CD4+ T cells in susceptible BALB/c mice occurs after infection with Leishmania major (L. major). Since little is known about the involvement of IL-9, the possible role of this cytokine with regard to its immunregulatory function was evaluated by comparing its presence in the serum and its expression kinetics in spleen and lymph nodes in resistant and susceptible mice. To this sera of L. major-infected mice were tested functionally for IL-9. In addition the PCR-aided detection of IL-9 mRNA in organs of mice and measurement of the lymphokine in supernatants of restimulated lymph node and spleen cell cultures were used. We show here that although no functionally active IL-9 was detected in sera of both BALB/c and C57BL/6 mice, IL-9 is produced after in vitro antigenic restimulation and its mRNA was found to be expressed in lymph nodes and spleens during an immune response against L. major. Shortly after infection no principal differences in the kinetics of IL-9 expression could be observed, which had its maximum between day 5 and 7 after infection. The rate of production however was higher in the susceptible BALB/c mice. In athymic BALB/c nu/nu mice and in mice depleted of CD4+ T cells no IL-9 production was detectable in vivo at the level of mRNA and no IL-9 was produced after stimulation with L. major antigen in vitro. Treatment of infected mice with cyclosporin A ablates antigen-specific IL-9 production when tested in vitro without affecting its production after polyclonal T cell stimulation. Positively selected, purified CD4+ T cells were fully capable of producing IL-9. From 4 weeks after infection, IL-9 synthesis was observed only in BALB/c mice, correlating with the expansion of antigen-specific Th2 type T helper cells in these mice. Treatment of BALB/c mice with neutralizing anti-IL-4 mAb, a regimen known to lead to subsequent cure of infected BALB/c mice, suppressed late IL-9 synthesis.

Expression of the murine interleukin-4 gene in an attenuated aroA strain of Salmonella typhimurium: persistence and immune response in BALB/c mice and susceptibility to macrophage killing

Cytokines are potentially useful in vaccination as adjuvants or modulators of the type of response induced. The work below describes the expression of a cloned cytokine gene for murine interleukin-4 (mIL-4) by a live vaccine vector, an attenuated aroA strain (SL7207) of Salmonella typhimurium, in a murine model system. SL7207 was used as a carrier for two different high-level expression vectors. Both resulting strains, designated SL7207(pOmpAmIL-4) and SL7207(pKKmIL-4), expressed the cloned gene product as monitored by both immunological and biological assays. However, SL7207(pOmpAmIL-4) produced mIL-4 at higher levels and was more stable in vitro than SL7207(pKKmIL-4). When SL7207(pOmpAmIL-4) was used as a live vaccine in BALB/c mice, this strain grew and survived at higher levels than the parental attenuated strain or empty plasmid-carrying strain in spleens, livers, and intestines. This difference in growth and survival did not appear to be caused by alterations in specific lymphocyte-mediated anti-Salmonella immune responses such as delayed-type hypersensitivity or serum antibody as measured by enzyme-linked immunosorbent assay; such alterations have been induced by IL-4 administration in other in vivo systems, and the lack of effect here may reflect the fact that IL-4 is not secreted from the bacteria in large quantities, most of the cytokine being in the cytoplasmic-membrane-bound fraction. Conversely, the ability of mouse macrophages to kill the bacteria in vitro was inhibited by bacterial production of mIL-4. This reduction in macrophage killing activity suggests that bacterial production of mIL-4 may be detrimental to host defense against Salmonella infection and may explain the enhanced bacterial growth and survival in vivo.

Cytokines in leishmaniasis: a complex network of stimulatory and inhibitory interactions

The work of immunologists, cell biologists and parasitologists in the field of leishmaniasis has not only provided important insights into the immunopathogenesis of this disease, but also yielded fundamental contributions to our understanding of basic immunological phenomena and of host-parasite interactions. The ability of recombinant interferon-gamma to induce the microbicidal activity of phagocytes and the opposite effect of inhibitory cytokines was first demonstrated with Leishmania-infected macrophages. The selective development of protective and disease-mediating CD4+ T lymphocytes as well as their differential influence on the course of the disease has been long investigated in the murine Leishmania major model and now represents one of the best examples for the in vivo induction of type 1 versus type 2 T helper lymphocytes. At the same time, this model has also been extensively used for immunization studies and cytokine therapy, which shed light on the functions of cytokines in vivo as well as on the mechanism(s) of disease resistance and susceptibility. In this review we will discuss the present picture of the cytokine network in murine L. major infections.

T-cell-T-cell collaboration in allograft responses

T-cell-T-cell collaboration in allogeneic responses traditionally has been viewed as the requirement for CD4+ T helper cells in the activation of CD8+ cytotoxic T cells. In this regard, the role of the CD4+ T cell is primarily to provide growth factors, such as interleukin-2, on which the CD8+ T cell is dependent. However, expanding information concerning the function of T-cell subsets, and the roles of antigen-presenting cells and cytokines in regulating immune responses, requires that the basic tenets of T-cell interactions be re-evaluated.

Molecular mechanisms used by tumors to escape immune recognition: immunogenetherapy and the cell biology of major histocompatibility complex class I

In this article, we explore the hypothesis that tumor cells can escape recognition by CD8+ T cells via deficiencies in antigen processing and presentation. Aspects of the molecular and cellular biology of major histocompatibility complex class I are reviewed. Evidence for histology-specific molecular mechanisms in the antigen-processing and -presentation deficiencies observed in some human and murine tumors is presented. Mechanisms identified include down-regulation of antigen processing, loss of functional beta 2-microglobulin, and deletion of specific alpha-chain alleles. Finally, we discuss studies using an antigen-presentation-deficient mouse tumor as a model for the immunogenetherapy of an antigen-presentation deficiency.

The role of natural killer cells in innate resistance to infection

Natural killer cells were first identified by their cytotoxic activity against tumor cells, suggesting a role in immunological surveillance against neoplasia. However, there is now increasing evidence that natural killer cells are important mediators of innate resistance against a variety of pathogenic micro-organisms. Recently, several important advances have been made in our understanding of how these cells are activated during infection, the contribution of cytokines derived from natural killer cells to host resistance and their influence on the development of antigen-specific T-cell responses.

T-cell and cytokine responses in leishmaniasis

Intracellular pathogens, particularly those that inhabit lymphocytes and macrophages, represent unique challenges to the immune system. Leishmania are protozoan parasites that replicate exclusively in macrophages and are thus in an excellent position to influence lymphocyte responses. T cell responses are critical in determining the outcome of infections with Leishmania. In both murine and human infections, strong T helper type 2 responses have been associated with disease, and a decreased or absent T helper type 2 response has been associated with healing.

Natural killer cells are a source of interferon gamma that drives differentiation of CD4+ T cell subsets and induces early resistance to Leishmania major in mice

Infection of mice with the protozoan Leishmania major provides an excellent model to define the factors involved in T helper (Th) subset development, since Th1 cells confer protection in resistant strains of mice, whereas Th2 cells are associated with the fatal outcome of susceptible mice. We previously found that interferon gamma (IFN-gamma) was required for Th1 cell development after infection of mice with L. major. In this report, we evaluate the contribution of natural killer (NK) cells to IFN-gamma levels early in L. major infection. NK cell activity was higher in resistant C3H/HeN mice than in susceptible BALB/c mice during the first week of infection, and removal of NK cells significantly decreased IFN-gamma levels and promoted interleukin 4 (IL-4) production in both the draining lymph nodes and spleen. IFN-gamma production by NK cells required the presence of CD4+ T cells or IL-2, but not CD8+ T cells. Enhanced disease, as measured by parasite numbers and lesion development, was observed in NK cell-depleted mice. Furthermore, a comparison of the NK cell response and the subsequent parasite burden in several inbred strains of mice demonstrated that NK cells mediate early resistance to L. major. Together, these data indicate that the stimulation of NK cells, through the production of IFN-gamma, plays an important role in initiating Th1 cell differentiation in leishmaniasis and in controlling early resistance to L. major.

Adoptive transfer of low numbers of CD4+ T cells into SCID mice chronically treated with soluble IL-4 receptor does not prevent engraftment of IL-4-producing T cells

After intravenous injection of 10(5) purified, lymph node (LN)-derived dm2 (H-2d/Ld-) CD4+ T cells into young C.B-17 scid/scid (severe combined immunodeficiency, SCID) mice (H-2d/Ld+), the transplanted Ld-T cells show a selective pattern of engraftment: they repopulate the spleen, the lamina propria of the small intestine and the mesenteric LN (but not other peripheral LN) of the immunodeficient host. CD4+ cells repopulating different lymphoid organs of the SCID recipient mice produce interleukin-2 (IL-2) and interleukin-4 (IL-4) in response to polyclonal stimulation in vitro. Some evidence has recently been provided that cytokines (e.g. IL-4) present at the site of antigen stimulation in vivo decisively influence the pattern of cytokines expressed by T cells activated at these sites. We therefore asked if neutralization of IL-4 by chronic treatment of SCID mice with high doses of recombinant soluble IL-4 receptor (sIL-4R) changes the IL-4 or IL-2 expression pattern of CD4+ T cells adoptively transferred into young SCID recipients. Transplanted SCID mice were chronically treated with two different, recombinant murine sIL-4R proteins. The experimental series further included groups of transplanted SCID mice treated with a recombinant human sIL-4R protein (which does not bind murine IL-4), treated with the anti-murine IL-4 monoclonal antibody (MoAb) 11B11, or non-treated. Transplanted SCID mice treated with the recombinant murine sIL-4R protein preparations displayed detectable sIL-4R serum levels, which demonstrates that the substitution therapy could maintain neutralizing serum levels of anti-IL-4 activity in SCID mice. By contrast, no serum sIL-4R levels were detectable in the sensitive ELISA readout in transplanted SCID mice which were non-treated, treated with the MoAb 11B11, or treated with the recombinant humans sIL-4R protein. The efficiency and the pattern of CD4+ T-cell engraftment, and the lymphokine-producing phenotype of the engrafted dm2 CD4+ cells, was not affected by the continuous IL-4-neutralizing treatment of mice with either the MoAb 11B11 or the soluble IL-4R preparations. Hence, in contrast to the published evidence of the dramatic effect of IL-4 on the lymphokine-producing phenotype of CD4+ T cells stimulated in vitro or in vivo, the chronic suppression in vivo of IL-4 activity (by either different sIL4-R protein constructs, or by the anti-IL-4 MoAb 11B11) did not lead to preferential engraftment of Th1-type CD4+ T cells after adoptive transfer of CD4+ T-cell populations into an immunodeficient recipient.

Rheumatoid inflammatory T-cell clones express mostly Th1 but also Th2 and mixed (Th0-like) cytokine patterns

This study was performed in order to characterize whether T cells from rheumatoid synovial inflammation belong to the Th1- or Th2-like functional subsets. Cytokine production was studied in 26 CD4+ alpha beta+ and 2 CD8+ alpha beta T-cell clones from the synovial fluid, the synovial membrane and peripheral blood of 5 patients. Fifteen of the CD4+ clones were raised against various mycobacterial antigens and 11 CD4+ clones and 2 CD8+ clones were raised unspecifically using PHA and/or IL-2. The specificities of these clones are not known. In the mycobacterial antigen-specific group, all CD4+ alpha beta T-cell clones produced IFN-gamma at high levels, while the production of IL-4 was generally absent or low (< 1 ng/ml), consistent with a Th1-like profile. Some of these clones, however, also produced various amounts of IL-10 which has been regarded as a Th2 product but can be produced also in lower amounts by Th1 cells. One HSP-65-specific clone produced levels of IL-4 and IL-10 in the same order as that of IFN-gamma, thus appearing to be Th0-like. Among the 11 unspecific CD4+ clones, 7 showed a Th1-like pattern but with lower levels of IFN-gamma than the antigen-specific clones. However, three clones did not produce any IFN-gamma activity but produced IL-4 and one of them also produced distinct amounts of IL-10, compatible with a Th2-like pattern. In addition, one of the clones also showed an almost equally strong IFN-gamma and IL-4 production, thus most likely representing a Th0-like clone.

Leishmania major-specific, CD4+, major histocompatibility complex class II-restricted T cells derived in vitro from lymphoid tissues of naive mice

Several studies indicate that the outcome of experimental murine cutaneous leishmaniasis caused by Leishmania major (Lm) is determined by immunological events occurring shortly after infection. These events lead to outgrowth of either protective CD4+ T cells in the C57BL/6 mouse, which cures, or exacerbative cells in the BALB/c mouse, which succumbs to disease. Potential factors influencing the outgrowth of protective or exacerbative T cells include antigen-presenting cells (APC), cytokines, and parasite antigens. An in vitro system, in which one could precisely control the factors shaping early events in the T cell response to Lm, would be very useful. To this end, we have examined the in vitro response of naive lymphocytes to Lm promastigotes. The data presented here show that Lm-specific CD4+ T cell receptor alpha/beta + T cells can be generated in vitro from spleen and lymph node cell populations of naive mice. Furthermore, they can be obtained from the CD44low (unprimed) population of T lymphocytes, indicating that in vitro priming occurs. The ability to generate these T cells is dependent on the presence of live parasites and is not due to a parasite-derived nonspecific T cell mitogen. Restimulation, as assayed by proliferation, requires APC bearing syngeneic I-A. Optimal restimulation of the in vitro derived T cells is achieved only when live promastigotes are used. The T cells do not proliferate in response to a frozen-and-thawed lysate of promastigotes, yet they exhibit mild reactivity to lysates prepared from heat-shocked promastigotes. Furthermore, they do not recognize two predominant antigens on the promastigote surface, lipophosphoglycan and gp63. T cells derived in vitro with Lm show crossreactivity with live L. donovani, less crossreactivity with live L. mexicana, and no crossreactivity with live Bacillus-Calmette-Guerin or live Brugia malayi microfilariae. Finally, these early T cells, whether derived from healing C57BL/6 or nonhealing BALB/c mice, produce interleukin 2 (IL-2), IL-4, and interferon gamma.

Selective differentiation of CD4+ T helper cell subsets

During the past year significant advances have been made in our understanding of the factors contributing to the differentiation of CD4 T helper cell subsets. These have been driven, in part, by the realization that signals (cytokines) from the innate immune response are critical in T cell subset differentiation. In addition, several studies have also elucidated how the antigen-presenting cell, the antigenic epitope and the antigen concentration may contribute to the selective development of a particular T helper cell subset.