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

Decreased serum levels of TGF-beta in patients with acute Plasmodium falciparum malaria

Apart from cellular immunity and immunopathology, various cytokines have been implicated in malaria-associated immunosuppression. In this study, serum levels of transforming growth factor-beta (TGF-beta) were determined with an enzyme-linked immunosorbent assay in 37 patients with acute Plasmodium falciparum malaria prior to, during, and after therapy and in 17 healthy controls in Bangkok, Thailand. Patients were treated with artesunate and mefloquine. TGF-beta serum levels were found decreased prior to treatment (14 +/- 11 pg/ml versus 63 +/- 15 pg/ml in healthy controls; P < 0.05). The serum concentrations of TGF-beta increased after initiation of treatment and were within normal range on day 21. Serum levels of both tumor necrosis factor-alpha (TNF-alpha) and soluble TNF-receptor 55 kDa were inversely correlated to serum levels of TGF-beta (r = -0.667 and r = -0.592, n = 37; respectively, P < 0.05 for both). No correlation between parasitemia and serum levels of TGF-beta could be found. The results are compatible with a decreased production and release, an enhanced clearance or utilization, or tissue accumulation of TGF-beta in acute P. falciparum malaria.

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.

Interferon gamma and interleukin 4 secreting cells in the gastric antrum in Helicobacter pylori positive and negative gastritis

Little is known of the function of the T cells in the inflammatory infiltrate in Helicobacter pylori associated gastritis. This study thus measured T cell in vivo activation by enumerating the frequency of interferon gamma (IFN gamma) and interleukin 4 (IL 4) secreting cells isolated from the gastric antral mucosa in patients with or without gastritis and in H pylori positive and negative gastritis. Fifty four samples were examined for cytokine secretion. Four antral biopsy specimens from each patient (n = 51) were taken during diagnostic endoscopy. One was used to estimate histological gastritis and the presence of H pylori, and three of the samples were used to isolate T cells by enzymatic digestion. IFN gamma and IL 4 secreting cells were enumerated by ELISPOT. Thirty four samples had gastritis and 79% of those were H pylori positive. None of the samples from non-inflamed mucosa had H pylori. The numbers of IFN gamma secreting cells per 10(5) T cells were higher in gastritis than in normal mucosa (145 v 20 IFN gamma spots, p < 0.01), and higher in H pylori negative than H pylori positive gastritis (371 v 110 IFN gamma spots, p < 0.05). The frequencies of IL 4 secreting cells did not differ between gastritis and non-inflamed mucosa. In conclusion, there is an increase in IFN gamma secreting cells but not in IL 4 secreting cells in H pylori positive and negative gastritis. It is not known if this TH1 type reaction has a pathogenetic or protective role.

Regulation of the interaction between Th1 and Th2 T cell clones to provide help for antibody production in vivo

On the premise that an individual with an intact immune system has the capability to develop both cellular and antibody immune responses supported by the balance between the lymphokines secreted by T helper (Th) cells, we studied the interaction between different types of Th cell clones in vivo and the parameters that may affect this interaction. We used an adoptive transfer system in which nude or lethally irradiated mice were reconstituted with histocompatible CD4+ keyhole limpet hemocyanin (KLH)-specific T cell clones with defined lymphokine profiles. This approach allowed us to study the effects of the cognate interaction between T and B cells in the presence of a defined set of lymphokines. We demonstrated that the co-transfer of both subsets of Th cells resulted in increased production of IgA, and decreased production of IgE and IgG2a. The concomitant presence of both cell types also increases their functional survival in vivo. We have shown that in the presence of a Th2 clone, higher immunization doses (above 100 micrograms trinitrophenol (TNP)-KLH/mouse) result in increased production of IgE and IgG1. In contrast, when a Th1 clone is present, low immunization doses (less than 50 micrograms TNP-KLH/mouse) resulted in increased production of IgG2a. We were also able to show that the neutralization of interleukin-4(IL-4) and or interferon-gamma (IFN-gamma) was sufficient to abrogate most of the regulatory effects caused by the Th2 or the Th1 clone respectively. Our results indicate that the subset of T cell(s) transferred determines the type of response obtained. In addition, the data presented indicate that the antigen dose used for immunization can modulate the quantitative parameters of the response. Furthermore, we have shown that the interaction between the two subsets of T cells in vivo is characterized by both antagonistic and agonistic effects and that most of the regulatory effects exerted by one subset over the other are mediated by IL-4 or IFN-gamma.

Cytokine-induced differentiation of precursor mouse CD8+ T cells into cytotoxic CD8+ T cells secreting Th1 or Th2 cytokines

Alloantigen-stimulated CD8+ mouse spleen cells, either spontaneously or in the presence of IL-12 or IFN gamma plus anti-IL-4, differentiate into CD8+ T cells secreting a Th1-like cytokine pattern (IL-2 and IFN gamma). IL-4 induced differentiation into CD8+ T cells secreting Th2 cytokines (IL-4, IL-5, IL-6, and IL-10), whereas anti-IFN gamma suppressed the development of CD8+ cells secreting IFN gamma. Clones of IL-4- or IFN gamma-producing CD8+ T cells were relatively stable, as IL-4 or IFN gamma did not cause interconversion of committed CD8+ T cells. Both CD8+ subsets were cytotoxic, failed to provide cognate help for B cell antibody production, and remained CD4-, CD8 alpha+ CD8 beta+. We propose the names TC1 and TC2 for cytotoxic CD8+ T cells secreting Th1-like and Th2-like cytokines, respectively.

Cytokine gene expression during infection of mice lacking CD4 and/or CD8 with Trypanosoma cruzi

The expression of lymphokine genes during infection of virulent (Tulahuén) or mild (CA-I) strains of T. cruzi was studied in mice lacking CD4 and/or CD8 molecules. The increased susceptibility of CD4- and CD4-CD8- mice to infection with CA-I or Tulahuén was parallelled by diminished IFN-gamma mRNA levels. Nitric oxide release and inducible nitric oxide synthase mRNA accumulation by cells from Tulahuén infected CD4- mice was also diminished. CD8- (but not CD4-CD8- mice) showed an increased IL-4 and IL-10 mRNA accumulation upon infection with both strains of T. cruzi. A 'Th2-like' response (higher IL-4 and IL-10 mRNA to IFN-gamma mRNA ratio), was also observed when cells from noninfected CD8- mice were stimulated with T cell mitogens.

Sunlight induced progression of AIDS

Ultraviolet B (UVB) radiation in sunlight damages the cutaneous immune system of individuals primarily by converting trans-urocanic acid (UCA) to its cis isoform which in turn instigates excessive local, and eventually systemic, levels of tumor necrosis factor-alpha (TNF alpha). UVB radiation and TNF alpha have been found to activate HIV from the latent state, and TNF alpha has been implicated in the pathogenesis of several manifestations of the acquired immune deficiency syndrome (AIDS). We hypothesize that the immunosuppressant properties of TNF alpha and cis-UCA, released by intense sun exposure, can accelerate the onset and progression of AIDS in HIV-infected individuals.

Modulation of the antilisterial activity of human blood-derived macrophages by activating and deactivating cytokines

A concept of macrophage deactivation by hormones and cytokines that opposes activation was recently proposed. Deactivation of the antilisterial activity of macrophages by IL-4, IL-10, and TGF-beta, as well as by dexamethasone, was studied here. IL-4, IL-10, and dexamethasone, but not TGF-beta, caused a complete loss of the competence of human blood-derived macrophages infected with Listeria monocytogenes to control or eliminate ingested bacteria. IL-10 and, to a lesser degree, dexamethasone lessened in parallel the capacity of macrophages to secrete H2O2. The antilisterial activity of cells simultaneously exposed to deactivating agents could be significantly augmented by IFN-gamma. Likewise, TNF-alpha and to a limited degree GM-CSF increased the antilisterial activity of cells treated with IL-10 and dexamethasone but not that of cells treated with IL-4. Suppression of TNF-alpha secretion in response to Listeria by TGF-beta, IL-10, dexamethasone, or pentoxifylline did not closely parallel antilisterial activity. Studies by transmission electron microscopy and actin staining suggested that deactivation by IL-10, IL-4, and dexamethasone of human blood-derived macrophages resulted in intraphagosomal multiplication of Listeria followed only then by an escape of bacteria into the cytoplasm. The antibacterial competence of human macrophages is lessened by IL-4 and IL-10 and augmented by IFN-gamma, TNF-alpha, and GM-CSF. The success of human macrophages in controlling intracellular pathogens appears to depend on the balance of activating and deactivating mediators modulating their activity.

T cell genetic background determines default T helper phenotype development in vitro

A host's ability to resist certain pathogens such as Leishmania major can depend upon the phenotype of T helper (Th) subset that develops. Different murine genetic backgrounds are known to significantly alter the direction of Th subset development, although the cellular basis of this influence is poorly understood. To examine the basis of this effect we used an in vitro alpha/beta-T cell receptor (TCR) transgenic system for analysis of Th phenotype development. To control for TCR usage, we derived the DO11.10 alpha/beta-TCR transgene in several genetic backgrounds. Our findings suggest that the effects of genetic background on Th phenotype development reside within the T cell, and not the antigen-presenting cell compartment. Transgenic T cells from both the B10.D2 and BALB/c backgrounds showed development toward either the Th1 or Th2 phenotype under the strong directing influence of interleukin (IL) 12 and IL4, respectively. However, when T cells were activated in vitro under neutral conditions in which exogenous cytokines were not added, B10.D2-derived T cells acquired a significantly stronger Th1 phenotype than T cells from the BALB/c background, correspondent with in vivo Th responses to Leishmania in these strains. Importantly, these cytokine differences resulted in distinct functional properties, because B10.D2- but not BALB/c-derived T cells could induce macrophage production of nitric oxide, an important antimicrobial factor. Thus, the genetically determined default Th phenotype development observed in vitro may correspond to in vivo Th subset responses for pathogens such as Leishmania which do not initiate strong Th phenotype-directing signals.

Differential production of interferon-gamma and interleukin-4 in response to Th1- and Th2-stimulating pathogens by gamma delta T cells in vivo

Exposure to various pathogens can stimulate at least two patterns of cytokine production by CD4-positive T cells. Responses that result in secretion of interferon-gamma (IFN-gamma), lymphotoxin and interleukin-2 (IL-2) are classified as T-helper-1 (Th1); CD4+ T-cell production of IL-4, IL-5, IL-9, IL-10 and IL-13 is called a T-helper-2 response (Th2). Differentiation of CD4+ T cells into either Th1 or Th2 cells is influenced by the cytokine milieu in which the initial antigen priming occurs. Here we use flow cytometry to identify the presence of intracellular cytokines (cytoflow) and analyse T-cell production of IFN-gamma and IL-4 from mice infected with Listeria monocytogenes or Nippostrongylus brasiliensis. We show that T cells bearing gamma delta receptors discriminate early in infection between these two pathogens by producing cytokines associated with the appropriate T-helper response. Our results demonstrate that gamma delta T cells are involved in establishing primary immune responses.

Elevated interleukin-10 levels in patients with rheumatoid arthritis

OBJECTIVE

Interleukin-10 (IL-10) has been shown to exert both antiinflammatory and immunostimulatory effects in vivo and in vitro. We therefore sought to examine the role of this cytokine in rheumatoid arthritis (RA) by assessing serum and synovial fluid IL-10 levels.

METHODS

Serum and synovial fluid samples were collected from patients with RA and patients with various inflammatory, infectious, and noninflammatory arthritides (controls). IL-10 was assayed using an IL-10-specific enzyme-linked immunosorbent assay, and messenger RNA (mRNA) levels were assessed by semi-quantitative polymerase chain reaction (PCR) techniques.

RESULTS

Both RA serum and synovial fluid contained significantly elevated IL-10 levels compared with levels in normal subjects or in control patients (P < 0.01). Some patients with spondylarthropathy also manifested increased serum levels of IL-10. Serum levels of IL-10 did not correlate with standard measures of clinical activity, but were shown to correlate significantly with serum rheumatoid factor (RF) titers and in vitro levels of spontaneous IgM-RF production (P < 0.05). PCR analyses demonstrated the constitutive expression of IL-10 mRNA by the non-T cell population, and semiquantitative PCR analysis documented elevated levels of IL-10 mRNA in circulating mononuclear cells of those RA patients who were not treated with slow-acting antirheumatic drugs. Analysis of IL-10 mRNA revealed the cytokine to be of human, and not viral, origin.

CONCLUSION

These data suggest that there is increased production of IL-10 by non-T cells in patients with RA. This may contribute to the diminished T cell function and increased antibody and RF production in these patients.

Soluble receptors for tumour necrosis factor in clinical laboratory diagnosis

Soluble tumour necrosis factor receptors (sTNF-Rs) play a role as modulators of the biological function of tumour necrosis factor-alpha (TNF-alpha) in an agonist/antagonist pattern. In various pathologic states the production and release of sTNF-Rs may mediate host response and determine the course and outcome of disease by interacting with TNF-alpha and competing with cell surface receptors. The determination of sTNF-Rs in body fluids such as plasma or serum is a new tool to gain information about immune processes and provides valuable insight into a variety of pathological conditions. Regarding its immediate clinical use, sTNF-Rs levels show high accuracy in the follow-up and prognosis of various diseases. In HIV infection and sepsis, sTNF-Rs concentrations strongly correlate with the clinical stage and the progression of disease and can be of predictive value. Determination of sTNF-Rs also gives useful information for monitoring cancer and autoimmune diseases. The information provided is often even superior to that obtained with classical disease markers, probably due to the direct involvement of the "TNF system" in the pathogenetic mechanisms in these patients. The available data imply that the measurement of sTNF-Rs, especially of the sTNF-R 75kD type, is a useful adjunct for quantification of the Th1-type immune response, similar to other immune activation markers such as neopterin and beta 2-microglobulin. Endogenous sTNF-Rs concentrations appear to reflect the activation state of the TNF-alpha/TNF receptor system.

Identification and characterization of a novel GGA/C-binding protein, GBP-i, that is rapidly inducible by cytokines

Immunosuppressive states with accompanying alterations in cytokine profiles have been postulated to play a vital role in the reactivation of viruses from latency. Cytokines regulate gene expression by activating transcription factors via well-characterized signal transduction pathways. In this study, we report the identification of a novel inducible protein, GBP-i, that binds to a double-stranded GGA/C-rich region of the transcriptional control region of the human papovavirus JC virus (JCV), specifically within the origin of viral DNA replication. GBP-i is distinct from previously characterized GC-box-binding proteins with respect to both its sequence specificity and its electrophoretic mobility on native and denaturing gels. GBP-i responds within 90 min to phorbol myristate acetate stimulation; however, unlike typical phorbol myristate acetate-inducible factors, this rapid induction is regulated primarily at the transcriptional level. Further, the induction of GBP-i appears to be widespread and mediated by many inflammatory cytokines, including interleukin-1 beta, tumor necrosis factor alpha, gamma interferon, and transforming growth factor beta. Interestingly, the induced protein acts as a transcriptional repressor in its native context in the JCVL promoter. However, when its binding sequence is transposed to a heterologous promoter, GBP-i appears to function as a transcriptional activator. The data presented here suggest a role for GBP-i in cytokine-mediated induction of viral and cellular genes.

Dysregulation of interleukin 8, interleukin 10, and interleukin 12 release by alveolar macrophages from HIV type 1-infected subjects

We examined the in vitro release of interleukin 8 (IL-8), interleukin 10 (IL-10), and interleukin 12 (IL-12) by alveolar macrophages from normal volunteers and HIV-1-infected subjects. Normal volunteers had very low levels of IL-8 and IL-10 and undetectable IL-12 in the cell-free bronchoalveolar lavage fluid (BALF). Asymptomatic HIV-1-infected subjects had elevated levels of IL-8 and IL-10 in their BALF, and HIV-1-infected subjects with nonspecific interstitial pneumonitis (NIP) or infected with Pneumocystis carinii had the highest BALF levels of IL-10 and IL-8. It was found that alveolar macrophages from asymptomatic HIV-1 subjects and from NIP subjects spontaneously released elevated IL-8, IL-10, and IL-12. However, AIDS subjects infected with P. carinii had cells that released elevated levels of IL-10 and IL-8, but low levels of IL-12. When alveolar macrophages were stimulated with Staphylococcus aureus Cowan (SAC), cells from normal volunteers responded with a considerably increased release of IL-8, IL-10, and IL-12; cells from HIV-1-infected subjects without P. carinii infection responded with a moderate increase in release of all three monokines. SAC stimulation did not enhance the release of monokines by cells from AIDS subjects with P. carinii infection, and IL-12 levels remained low. There was no strict relationship between spontaneous cytokine release and p24 HIV-1 antigen expression by alveolar macrophages. Finally, we showed that neutralizing IL-10 production by alveolar macrophages from AIDS subjects substantially increased IL-12 releasability.(ABSTRACT TRUNCATED AT 250 WORDS)

The Th1-Th2 hypothesis of HIV infection: new insights

In their earlier, much quoted, viewpoint article, Mario Clerici and Gene Shearer examined the role of T helper 1 (Th1)- and Th2-type responses in immune dysregulation associated with human immunodeficiency virus (HIV) infection. In this article, they consider the complications of a Th1-Th2 model raised by the nomenclature, discuss the issue of cytokine production by non-T cells, and compare data obtained from T-cell clones with heterogeneous populations of leukocytes from patients. They define Th-cell responses and cytokine profiles as 'type 1' and 'type 2', and reemphasize the importance of strong cellular immune responses, along with the cytokines that augment and maintain such responses, in protective immunity against HIV infection and AIDS progression. Finally, they present a model of activation-induced, cytokine-modulated, programmed cell death as a major factor in the pathogenesis of HIV infection and AIDS.

Lymphocytic choriomeningitis virus-induced immune dysfunction: induction of and recovery from T-cell anergy in acutely infected mice

Acute infection of immunocompetent mice by lymphocytic choriomeningitis virus induces a potent cytotoxic T-lymphocyte response that eliminates infectious virus. Concurrently and paradoxically, there is a general suppression of lymphocyte responses to mitogens and to other infectious agents. Splenocytes from infected mice released significant amounts of gamma interferon in response to mitogenic stimulation in vitro, but neither interleukin 2 nor interleukin 4 was similarly elevated relative to the amounts released by control cells. Early T-cell receptor-proximal signaling events were found to be intact, confirming that the cells were viable and had received the mitogenic stimuli in an appropriate manner. Acutely infected adult thymectomized mice regained concanavalin A responsiveness in parallel with euthymic mice, if T cells were left unmanipulated for several weeks after clearance of virus from the mice. Therefore, although acute lymphocytic choriomeningitis virus infection has the effect of disrupting proliferation when the T-cell receptor is ligated, this state is only temporary. In contrast, T cells from persistently infected adult mice reveal long-lasting alterations in concanavalin A responsiveness.

Identification and characterization of a novel GGA/C-binding protein, GBP-i, that is rapidly inducible by cytokines

Immunosuppressive states with accompanying alterations in cytokine profiles have been postulated to play a vital role in the reactivation of viruses from latency. Cytokines regulate gene expression by activating transcription factors via well-characterized signal transduction pathways. In this study, we report the identification of a novel inducible protein, GBP-i, that binds to a double-stranded GGA/C-rich region of the transcriptional control region of the human papovavirus JC virus (JCV), specifically within the origin of viral DNA replication. GBP-i is distinct from previously characterized GC-box-binding proteins with respect to both its sequence specificity and its electrophoretic mobility on native and denaturing gels. GBP-i responds within 90 min to phorbol myristate acetate stimulation; however, unlike typical phorbol myristate acetate-inducible factors, this rapid induction is regulated primarily at the transcriptional level. Further, the induction of GBP-i appears to be widespread and mediated by many inflammatory cytokines, including interleukin-1 beta, tumor necrosis factor alpha, gamma interferon, and transforming growth factor beta. Interestingly, the induced protein acts as a transcriptional repressor in its native context in the JCVL promoter. However, when its binding sequence is transposed to a heterologous promoter, GBP-i appears to function as a transcriptional activator. The data presented here suggest a role for GBP-i in cytokine-mediated induction of viral and cellular genes.

Interactions between murine AIDS (MAIDS) and toxoplasmosis in co-infected mice

We coinfected C57B1/6 mice with LP-BM5 murine leukaemia viruses, responsible for murine AIDS (MAIDS), and an avirulent strain of Toxoplasma gondii. Virus-infected mice were infected perorally on day 30 with 10 cysts of T. gondii, and T. gondii-infected mice were challenged with LP-BM5 on day 20, 30 or 60 after parasite inoculation. Uninfected and singly infected mice were used as controls. The kinetics of parasite burden in blood, lungs and brain, together with blood lymphocyte subsets, and spleen and lymph node weights, were serially determined in each group of mice. The kinetics of parasite counts in mice infected by LP-BM5 then by T. gondii were similar to those in mice infected by T. gondii only, except for lung counts, which reached higher values than in animals infected with T. gondii alone, then fell and re-increased until the end of the experiment. The only significant change in parasite burdens when mice were first infected by T. gondii and then by LP-BM5, compared with T. gondii controls, was an increase in lung counts in mice challenged with LP-BM5 20 days after T. gondii inoculation. Whatever the schedule of co-infection, the kinetics of lymphocyte subsets in co-infected mice differed from those in T. gondii- or LP-BM5-infected mice; in dually infected mice CD4+ and CD8+ cell counts were intermediate between values in mice singly infected by the parasite or the virus. Enlargement of spleen and lymph nodes, which is a major criterion of MAIDS progression, was significantly less marked in co-infected mice than in mice infected with LP-BM5 alone. These data point to cross-regulation of T. gondii and LP-BM5 infections, which results in increased susceptibility to T. gondii, and may alter the progression of MAIDS.

Cytokine measurements and interpretation of cytokine assays in human disease

Cytokines are powerful mediator and communication molecules capable of regulating a wide spectrum of biologic functions, including immune responses. Although the role of cytokines in the pathogenesis of human disease is not yet understood, assays for cytokines have become a common feature in research and clinical laboratories. However, numerous pitfalls accompany measurements of cytokine levels in body fluids and of cytokine synthesis or gene expression in tissue. Interpretation of results obtained in cytokine assays, especially those performed with pathologic specimens, is fraught with difficulties. While cytokine assays are clearly of value in monitoring patients treated with recombinant cytokines or receiving anticytokine therapy, the clinical significance of cytokine assays is not yet fully established. In this review, some of the complexities associated with cytokine monitoring are discussed. The crucial importance of understanding cytokine biology for meaningful assay interpretation is emphasized.

Interleukin-12 regulates the proliferation of Th1, but not Th2 or Th0, clones

Our results indicate that interleukin (IL)-12 is an important costimulator of antigen-dependent proliferation of murine Th1 clones. In addition, we demonstrate that IL-10 inhibits splenic antigen-presenting cell (APC)-dependent proliferation of Th1 clones, at least in part, via down-regulation of APC-derived IL-12. Moreover, the failure of activated B cells to provide costimulation via IL-12 accounts for their inability to support optimal proliferative responses of Th1 clones. We also show that IL-12 regulates the ability of Th1 clones to respond to IL-4 and enhances their proliferation in response to IL-2, IL-7, or IL-15. In contrast, Th2 and Th0 clones appear refractory to the effects of IL-12, on antigen-dependent or growth factor-induced proliferation.

Interleukin 4 receptor signaling in human monocytes and U937 cells involves the activation of a phosphatidylcholine-specific phospholipase C: a comparison with chemotactic peptide, FMLP, phospholipase D, and sphingomyelinase

Interleukin 4 (IL-4) diminishes cytokine activation of human macrophage. IL-4 binding to monocyte IL-4R is associated with protein kinase C (PKC) translocation to a nuclear fraction. The cleavage of diacyglycerol (DAG), an activator of PKC, from membrane phospholipids was investigated to define the proximal events of IL-4R signaling. IL-4 induced a statistically significant time-and dose-dependent generation of DAG. The IL-4-triggered production of DAG was not derived from phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis, since neither cytosolic calcium flux nor liberation of inositol phosphates was detected in response to IL-4. Experiments were performed using [14C-methyl]choline-labeled U937 cells and monocytes to determine whether IL-4R activated phospholipase C (PLC), PLD, or PLA2 to use membrane phosphatidylcholine (PC) to form DAG. IL-4 induced a time- and dose-dependent increase of phosphocholine (pchol) with concomitant degradation of membrane PC (p < 0.05 compared with control). The finding that the peak reduction of PC was equivalent to peak production of pchol suggested that IL-4R signaling involved the activation of a PC-specific PLC. Changes in choline (chol) or lyso-PC and glycerolphosphocholine, the respective products of PC cleavage by PLD or PLA2, were not detected in IL-4-treated cells. In contrast, exogenous PLD induced an increase in chol and concomitant loss of membrane PC. Additional investigation suggested that IL-4R signaling does not involve PLD. In cells labeled with L-lyso-3-PC 1-[1-14C]palmitoyl, PLD but not IL-4, increased the production of phosphatidic acid (PA) and phosphatidyl-ethanol when pretreated with ethanol. Propranolol, an inhibitor of phosphatidate phosphohydrolase, and calyculin A, a phosphatase 1 and 2A inhibitor, blocked DAG production in response to FMLP but not to IL-4. In propranolol pretreated cells, PMA but not IL-4 triggered the production of PA and lowered the amount of DAG. Evidence that PLA2 is not coupled to IL-4R is the detection of arachidonate production in response to FMLP but not to IL-4. Furthermore, IL-4R is not coupled to sphingomyelinase (SMase) since IL-4, unlike exogenous SMase, did not generate ceramide but induced the hydrolysis of PC to pchol that was comparable to exogenous PLC. In summary, IL-4R signaling in monocytes and U937 cells involves PLC and not PLD, PLA2, or SMase, and it uses PC and not PIP2 to form DAG.

Identification of an immunodominant 32-kilodalton membrane protein of Leishmania donovani infantum promastigotes suitable for specific diagnosis of Mediterranean visceral leishmaniasis

Sera from 35 patients suffering from Mediterranean visceral leishmaniasis (caused by Leishmania donovani infantum) and 59 patients with various forms of cutaneous leishmaniasis prevalent in the sub-Mediterranean countries (caused by Leishmania major, L. donovani infantum, or Leishmania tropica) were tested by immunoblotting and enzyme-linked immunosorbent assay (ELISA) with both membrane and soluble antigens prepared from L. donovani infantum parasites. Control sera were from healthy children (n = 41), adults with nonleishmanial diseases (n = 40), and patients with Chagas' disease (n = 12). A P32 antigen present in the membrane preparation from L. donovani infantum parasites was recognized by 95% of serum specimens from patients with Mediterranean visceral leishmaniasis but not by serum specimens from patients with cutaneous leishmaniasis or sera from control individuals. An ELISA with electroeluted P32 antigen was found to have a specificity and sensitivity of 94% in the serodiagnosis of Mediterranean visceral leishmaniasis. Healthy children with asymptomatic Leishmania infection were seronegative for the P32 antigen by ELISA. These results suggest that antibodies to P32 antigen develop only in patients with visceral leishmaniasis and that the P32 ELISA may be useful in areas where the disease is endemic for discriminating between patients with this disease and those with other clinical conditions.

Intrathecal synthesis of interleukin-10 (IL-10) in viral and inflammatory diseases of the central nervous system

The intrathecal synthesis of interleukin 10 (IL-10) was investigated in 120 paired cerebrospinal fluid (CSF) and serum specimens from patients with various inflammatory and non-inflammatory diseases of the central nervous system (CNS). IL-10 was not demonstrated in the sera, but detectable levels were found in the CSF from: patients with acute viral ("aseptic") meningitis, but only within 48-72 h of symptom onset; human immunodeficiency virus type 1 (HIV)-infected patients with HIV-related encephalitis/leukoencephalopathy or cryptococcal meningitis; a patient with primary B cell lymphoma of the CNS, and a patient with encephalomeningeal sarcoidosis (in whom IL-10 was demonstrated in all CSF collected over a period of 6-months). In chronic meningeal infections/inflammations, IL-10 seems to be continuously produced within the CSF. Our findings suggest that IL-10, a cytokine which exerts many immunosuppressive actions, may play different immunomodulatory roles in CNS diseases; in particular, its intrathecal synthesis may explain why some infectious and inflammatory meningeal diseases may have slow development and chronic evolution.

Alterations in interleukin-4 and antibody production following pheromone exposure: role of glucocorticoids

We have previously shown that exposure to pheromones from footshock-stressed mice suppresses cell-mediated immunity and enhances humoral immunity. Here we show that stress odor exposure is associated with enhanced antigen-specific antibody production and interleukin (IL)-4 production in BALB/c, but not C57Bl/6, mice. Glucocorticoid receptor antagonism blocks the enhancement of IL-4, but not antibody titers. There is an apparent differential sensitivity of BALB/c and C57Bl/6 spleen cells to in vitro incubation with the synthetic glucocorticoid dexamethasone; IL-2 production by BALB/c spleen cells is more sensitive to the effects of steroid. These data suggest that C57Bl/6 mice may not respond to stress pheromones due to their relative insensitivity to endogenous steroids.

Induction of humoral and cellular immunity to simian immunodeficiency virus: what are the requirements for protection?

In an effort to produce a strong humoral and cellular immune response that might protect against simian immunodeficiency virus (SIV) infection, groups of five rhesus macaques each were immunized intramuscularly at 0, 2 and 6 months with 100 micrograms of an inactivated preparation of SIV/Delta B670 in either an oil-in-water emulsion with Ribi Detox, containing mycobacterial cell wall skeleton and monophosphoryl lipid A (CWS/MPL) (group A) or a water-in-oil emulsion with incomplete Freund's adjuvant, containing CWS/MPL for the first two injections (group B). Animals were challenged with 10-100 monkey ID50 of monkey-cell-grown SIVmac251 3 months after the last injection, along with a group of four unvaccinated controls. Group B animals demonstrated the strongest immune responses following immunization, including neutralizing antibody titres against the challenge virus ranging from 160 to 320 and SIV-specific ELISA titres ranging from 10(5)-10(6) on the day of challenge, as well as strong in vitro lymphoproliferative and interleukin-2 (IL-2) production responses to the immunogen. Neutralizing antibody was not detectable in group A animals, ELISA titres were lower (10(2)-10(4)), no in vitro lymphoproliferative responses were observed, and in vitro IL-2 production was less pronounced. No protection against challenge was observed in either group. Moreover, group B animals exhibited a more pronounced clinical response following challenge than either group A animals or controls, consisting of hyperthermia and a greater degree of lymphadenopathy on day 7, followed by hypothermia and generally higher levels of serum viraemia on day 14.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Cytokines in the treatment of leishmaniasis: from studies of immunopathology to patient therapy

The genus Leishmania, an obligate intramacrophage parasite, causes a wide spectrum of clinical diseases. It is worldwide in distribution and causes 20 million new cases annually with an at risk population of approximately 1.5 billion persons. The most severe forms are associated with high morbidity, mortality and relapses with conventional therapy. The therapeutic issues and responses to standard and alternative therapies are reviewed. Recent developments in molecular biology and immunology methods employed in the study of leishmaniasis have defined an intricate interaction of the parasite with host immune system. Perturbation of the host immune responses may be part of the survival mechanisms of Leishmania. In murine model, the finding of T helper cells that differ by their panel of cytokines has allowed a more precise definition of immunopathogenesis of leishmaniasis. Preliminary data from leishmaniasis patients lend support to this concept of altered immunomodulation. Furthermore, the data from leishmaniasis patients lend support to this concept of altered enhancement of therapeutic response by interferon-gamma has provided a new approach for treatment of patients using recombinant cytokines and for the study of the disease. Current research for early diagnosis, alternative therapies and need for vaccines are reviewed in the context of the immunopathology of leishmaniasis.

Site-specific immunity to Leishmania major in SWR mice: the site of infection influences susceptibility and expression of the antileishmanial immune response

Inbred strains of mice usually develop either of two divergent patterns of infection in response to Leishmania major. Resistant mice, which develop self-limiting infections, respond immunologically with the activation of gamma interferon-secreting Th1 helper T cells, while nonhealing infections in susceptible mice are characterized by the proliferation of interleukin-4-secreting Th2 cells. Development of these divergent responses is dependent primarily on the strain of mouse infected, although factors such as the infective dose, species, and strain of parasite can also influence the degree of resistance. In this study, we show that a single mouse strain, SWR, can develop totally divergent patterns of infection depending on the site of parasite inoculation. Both SWR mice and highly susceptible BALB/c mice developed progressive, ultimately fatal disease when inoculated in the dorsal skin over the base of the tail. However, SWR mice infected in the hind footpad developed far less severe infections, which were for the most part controlled, whereas BALB/c mice infected in this site developed severe, nonhealing lesions. Production of gamma interferon and interleukin-4 and measurement of immunoglobulin E levels in serum were used to assess the degree of Th1 and Th2 cell activation in infected mice. Cytokine profiles early in infection had characteristics of a mixed Th1-Th2 response and were similar in SWR mice infected at either site. These early cytokine responses were not predictive of the ultimate disease outcome, since lymph node cells from healing mice eventually produced higher levels of gamma interferon than did those from nonhealing mice, and healing mice had lower levels of immunoglobulin E in serum, suggesting a functional bias toward Th1 cell activity in these animals. The differential ability of SWR mice to heal infections at different cutaneous sites provides a new model for the study of resistance to cutaneous leishmaniasis. Unlike traditional models of infection in which resistant and susceptible strains of mice are compared, this model allows for the study of factors that contribute to healing and nonhealing infections in a genetically identical strain of mouse.

Divergent T-cell cytokine patterns in inflammatory arthritis

A major immunoregulatory mechanism in inflammatory infections and allergic diseases is the control of the balance of cytokines secreted by Th1/Th2 subsets of T helper (Th) cells. This might also be true in autoimmune diseases; a Th2 pattern that prevents an effective immune response in infections with intracellular bacteria may favor immunosuppression in autoimmune disease. The pattern of cytokine expression was compared in the synovial tissue from patients with a typical autoimmune disease, rheumatoid arthritis, and with a disorder with similar synovial pathology but driven by persisting exogenous antigen, reactive arthritis. We screened 12 rheumatoid and 9 reactive arthritis synovial tissues by PCR and in situ hybridization for their expression of T-cell cytokines. The cytokine pattern differs significantly between the two diseases; rheumatoid arthritis samples express a Th1-like pattern whereas in reactive arthritis interferon gamma expression is accompanied by that of interleukin 4. Studying the expression of cytokines by in situ hybridization confirmed the results found by PCR; they also show an extremely low frequency of cytokine-transcribing cells. In a double-staining experiment, it was demonstrated that interleukin 4 is made by CD4 cells. These experiments favor the possibility of therapeutic intervention in inflammatory rheumatic disease by means of inhibitory cytokines.

Murine AIDS protects mice against experimental cerebral malaria: down-regulation by interleukin 10 of a T-helper type 1 CD4+ cell-mediated pathology

The retrovirus LP-BM5 murine leukemia virus induces murine AIDS in C57BL/6 mice that has many similarities with human AIDS; Plasmodium berghei ANKA causes experimental cerebral malaria in the same strain of mice. The outcome of malaria infection was studied in mice concurrently infected with the two pathogens. The retrovirus significantly reduced the gravity of the neurological manifestations associated with Plasmodium berghei ANKA infection. The protection against experimental cerebral malaria induced by murine AIDS increased with duration of viral infection and, hence, with the severity of the immunodeficiency. Interleukin 10, principally from splenic T cells, was shown to play a crucial role in this protection.

Consequences of secondary or co-infections for immunity

While remarkable progress has been made using genetically altered mice to understand the importance of different cytokines in protecting against experimental infections or co-infections, an examination of the opportunistic infections that occur during HIV infection of humans does not yet show a clear picture of cytokine imbalance. Opportunistic infections appear to result from impairments in cells mediating innate resistance, such as natural killer cells, macrophages, and neutrophils. Some of these defects may not be corrected even if CD4+ T cells were suddenly restored to normal. The lessons from immunodeficient and gene knockout mice now need to be put to the test in the clinic.

T cells which do not express membrane tumor necrosis factor-alpha activate macrophage effector function by cell contact-dependent signaling of macrophage tumor necrosis factor-alpha production

Previous studies have suggested that T cell contact-dependent signaling of macrophages (Mphi) is mediated by membrane tumor necrosis factor-alpha (memTNF-alpha), based on the observation that anti-TNF-alpha could inhibit T cell-mediated Mphi activation. The current report confirms that anti-TNF-alpha does inhibit activation of interferon-gamma (IFN-gamma)-primed Mphi by paraformaldehyde-fixed activated T cells. However, the involvement of membrane molecules other than memTNF-alpha in the contact-dependent signaling is suggested by two lines of evidence. First, the TH2 clone, AK8, displayed neither secreted TNF-alpha/beta nor memTNF-alpha/beta detectable by bioassay or immunofluorescence. Nonetheless, AK8 cells were equally effective, on a per cell basis, in contact-dependent signaling of M phi activation as TH2 and TH1 cells which do express memTNF-alpha. Second, the expression of memTNF-alpha by the TH2 clone, D10.G4, is maximal 24 h after activation, whereas the ability of this clone to activate Mphi is maximal at 6-8 of activation and declines thereafter. Since TNF-alpha is known to play a critical role in activation of Mphi effector function, it was hypothesized that T cell membrane components other than memTNF-alpha might signal Mphi production of TNF-alpha, thus allowing autocrine TNF-alpha stimulation of Mphi effector function. In support of this, it is demonstrated that paraformaldehyde-fixed activated TH2 cells can induce de novo production and release of TNF-alpha by Mphi. This effect was not an artifactual result of paraformaldehyde fixation since paraformaldehyde-fixed resting T cells did not induce TNF-alpha gene expression. Previous studies have demonstrated a role for autocrine TNF-alpha stimulation in LPS induction of effector function in recombinant IFN-gamma-primed Mphi. The current study confirms that TNF-alpha plays a critical role in T cell contact-dependent signaling of Mphi but indicates that memTNF on the T cells may not be a sine qua non factor for contact-dependent signaling. The data suggest that other T cell membrane molecules contribute to activation of Mphi effector function by stimulation of M phi TNF-alpha production.

Interleukin 13 and interleukin 4 protect bronchoalveolar macrophages from productive infection with human immunodeficiency virus type 1

In this study, we examined the impact of the predominantly Th2-type lymphokines interleukin 13 (IL-13) and interleukin 4 (IL-4) on acute infection of human bronchoalveolar macrophages with a macrophage-tropic isolate of human immunodeficiency virus type 1 (HIV-1). Addition of 0.01-10 ng of IL-4 or IL-13 per milliliters significantly blocked HIV-1 replication in infected cells, judging from levels of reverse transcriptase and p24 antigen in the supernatants of infected cells. Both IL-4 and IL-13 were almost as efficient as interferon-gamma (IFN-gamma) in preventing HIV-1 replication, when given in equivalent amounts. Moreover, neither IL-13 nor IL-4 interfered with the IFN-gamma-mediated enhancement of anti-HIV-1 activity in alveolar macrophages. Both IL-4 and IL-13 interfered with enhanced replication of HIV-1 in macrophages pulsed with the growth factor granulocyte-macrophage colony-stimulating factor (GM-CSF). Interleukin 13 also prevented HIV-1 release from peripheral blood mononuclear cells in a cocultivation experiment with feeder cells from a seronegative subject. These data suggest that Th2-derived lymphokines have significant anti-HIV-1 activity in cells of the macrophage lineage, although they may enhance the susceptibility of HIV-1-infected subjects to some opportunistic pathogens.

Non-cytotoxic, IL-4, IL-5, IL-10 producing CD8+ T cells: their activation and effector functions

CD8+ T cells activated in the presence of IL-4 can develop into distinct, non-cytotoxic CD8- and cytotoxic CD8+ subsets that produce IL-4, IL-5, IL-10 but do not produce IFN-gamma. These 'Th2 like' CD8+ cells may enhance Th2 responses, help B cells or suppress Th1 immune responses. Importantly, the switch from the cytotoxic, IFN-gamma producing CD8+ T-cell phenotype could compromise the host response to infectious agents such as HIV.

Role of cytokines in determining T-lymphocyte function

Early events in an immune response stimulate the production of cytokines that direct the subsequent development of T-helper (Th) subsets with discrete patterns of cytokine production. These events are dictated by the type of antigen/microorganism administered to a host, as well as dose and route of immunization. Bacterial stimuli activate macrophages of the innate immune response to produce IL-12 and drive Th1 development and cell-mediated immunity. Conversely, production of IL-4 early in an immune response favors a Th2 or allergic/humoral immune response. The ability of IL-4 and IL-10 to inhibit Th1 development and effector function, as well as the requirement of committed Th1 cells for co-stimulators to induce maximal IFN-gamma production, suggests that cell-mediated immunity is under strict control, probably to achieve immunity with minimum immunopathology.

NO as an effector molecule of parasite killing: modulation of its synthesis by cytokines

It has recently been appreciated that NO, a molecule previously known to play a physiologic role in blood pressure regulation, is a major effector molecule of macrophage cytotoxicity against a variety of microbial targets, including protozoan and helminth parasites. NO production by macrophages is arginine dependent and catalyzed by a cytokine-inducible form of the NO synthase. This activity is positively controlled by several up-regulatory stimuli (including IFN-gamma, TNF-alpha, IL-2) and negatively controlled by others (principally IL-10, IL-4, TGF-beta). Other cell types, such as endothelial cells and hepatocytes, display a similar capacity for NO production in response to cytokine stimulation. In murine models of leishmaniasis and schistosomiasis, in vivo NO synthesis correlates with protective immunity against infection. The effector molecule that plays a similar role in cell-mediated immunity in man has not yet been identified.

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.

Down-regulation of cytokine action

The study of cytokines that regulate all areas of cellular communication has expanded over the past few years. The control and modulation of the complex network of cytokine action remains an area of intense interest. Agents that will modulate cytokine signal transduction at the cellular level will assist in the understanding of the molecular basis of cytokine cellular activation and in the design of drugs for the management of clinical disease. Recent work has demonstrated the existence of complex mechanisms of negative regulation of cytokine action. New methods utilizing isolated protein products that participate in immunomodulation may prove useful for clinical regulation of the host response to cytokine up-regulation. Currently, most interest in soluble cytokine receptors, natural cytokine inhibitors, genetically engineered cytokine antagonists and single or combinations of anti-inflammatory cytokines has focused on the possibility that they may become standard pharmacological agents for the treatment of inflammatory complications of clinical disease. Specifically, TNF and IL-1 inhibitors and the cytokines IL-10 and TGF-beta, alone or in combination may be effective for the inhibition of severe clinical inflammation. Soluble receptors for other cytokines such as IL-6 may prove to be carrier proteins that enhance cytokine action and will require cautious investigation. Because most cytokines are pleiomorphic in their activities, down-regulation through the utilization of direct inhibitors or anti-inflammatory cytokines may cause immunosuppression, making the host susceptible to opportunistic infection. Selective and short-term inhibition of inflammatory cytokine action may be necessary to prevent unwanted clinical side-effects.

Natural autoantibodies, IgG antibodies to tetanus toxoid and CD5+ B cells in patients with Mediterranean visceral leishmaniasis. The Leishmania Study Group

Natural autoantibodies (NaAb) and IgG antibodies to tetanus toxoid (TT) were analysed in the sera of 38 children with active visceral leishmaniasis (VL) previously vaccinated with TT and in 30 healthy controls matched for sex and age. Patients exhibited high levels of NaAb to a panel of self antigens (tubulin, myosin, myoglobin, actin) contrasting to a low level of IgG to TT. Analysis of the circulating B cells in 26 untreated patients showed a low percentage of CD5+ per total B cells (3-66%, mean 36.6%) compared with 14 normal controls (17.8-66.6%, mean 52.7%) (P < 0.001). Evaluation of these parameters after antimonial therapy showed a significant decrease of the level of the NaAb (P < 0.0005), and a spontaneous increase of the level of the IgG to TT without any vaccine boosting (P < 0.01). In contrast, there was a significant increase in CD5+ B cells (P < 0.0005). This result suggests that CD5+ B cells may be sequestrated in parasitized lymphoid organs and may be released after remission. These findings show that the polyclonal B cell activation that occurs during active VL involves mainly B cells bearing NaAb and are in favour of a functional dichotomy of B cells.

CD4+ T-cell clones obtained from cattle chronically infected with Fasciola hepatica and specific for adult worm antigen express both unrestricted and Th2 cytokine profiles

The well-established importance of helper T (Th)-cell subsets in immunity and immunoregulation of many experimental helminth infections prompted a detailed study of the cellular immune response against Fasciola hepatica in the natural bovine host. T-cell lines established from two cattle infected with F. hepatica were characterized for the expression of T-cell surface markers and proliferative responses against F. hepatica adult worm antigen. Parasite-specific T-cell lines contained a mixture of CD4+, CD8+, and gamma/delta T-cell-receptor-bearing T cells. However, cell lines containing either fewer than 10% CD8+ T cells or depleted of gamma/delta T cells proliferated vigorously against F. hepatica antigen, indicating that these T-cell subsets are not required for proliferative responses in vitro. Seventeen F. hepatica-specific CD4+ Th-cell clones were examined for cytokine expression following concanavalin A stimulation. Biological assays to measure interleukin-2 (IL-2) or IL-4, gamma interferon (IFN-gamma), and tumor necrosis factor and Northern (RNA) blot analysis to verify the expression of IL-2, IL-4, and IFN-gamma revealed that the Th-cell clones expressed a spectrum of cytokine profiles. Several Th-cell clones were identified as Th2 cells by the strong expression of IL-4 but little or no IL-2 or IFN-gamma mRNA. The majority of Th-cell clones were classified as Th0 cells by the expression of either all three cytokines or combinations of IL-2 and IL-4 or IL-4 and IFN-gamma. No Th1-cell clones were obtained. All of the Th-cell clones expressed a typical memory cell surface phenotype, characterized as CD45Rlow, and all expressed the lymph node homing receptor (L selectin). These results are the first to describe cytokine responses of F. hepatica-specific T cells obtained from infected cattle and extend our previous analysis of Th0 and Th1 cells from cattle immune to Babesia bovis (W. C. Brown, V. M. Woods, D. A. E. Dobbelaere, and K. S. Logan, Infect. Immun. 61:3273-3281, 1993) to include F. hepatica-specific Th2 cells.

Protective immunity to Brucella ovis in BALB/c mice following recovery from primary infection or immunization with subcellular vaccines

Experiments were performed with BALB/c mice to elucidate the roles of humoral and cell-mediated immune responses in the acquisition of protective immunity to Brucella ovis and to compare infection immunity with immunity developed through vaccination with a hot saline extract (HS) of B. ovis. Mice convalescing from a primary infection with B. ovis displayed a high level of resistance to reinfection, as evidenced by splenic bacterial counts decreased over 10,000-fold from control groups at 2 weeks after challenge. Passive transfer assays revealed that protection was mediated by both T lymphocytes and antibodies but that antibodies had a substantially greater role on the basis of log units of protection that were transferred. Antibodies specific for HS proteins in sera from convalescent mice were predominantly of the immunoglobulin G 2a and 3 isotypes. Vaccination with HS conferred good protection against B. ovis, but protection was greatly enhanced by the incorporation of QS-21 or other adjuvants. Protection provided by the HS vaccine resulted largely from immune responses to its protein moieties. A critical evaluation of the protective efficacy of the rough lipopolysaccharide component of HS was precluded by its poor immunogenicity in BALB/c mice. HS-QS-21 afforded protection against challenge infection with B. ovis as good as that which developed after a primary infection and as good as or better than that provided by attenuated Brucella melitensis vaccine strain Rev 1. Passive transfer experiments confirmed that the magnitudes of both humoral and cell-mediated forms of protective immunity were equivalent in mice vaccinated with HS-QS-21 and those recovering from a primary infection. Protective immunity to B. ovis in mice therefore resembled that to Brucella abortus, except that the relative roles of humoral and cell-mediated immunity, rather than being equivalent, were shifted toward a greater role for antibodies.

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.