Human suppressor T cell clones lack CD28

Alloantigen-induced regulatory CD8+CD103+ T cells

Regulatory T cells (Tregs) appear of great importance in the balance between alloreactivity and tolerance and subsets of both CD4(+) and CD8(+) T cells have been recognized to function as regulatory T cells after allogenic transplantation. Among the CD8(+) T-cell subsets, the CD103(+) cells were most recently identified as regulatory. In this review, we describe their phenotypical and functional properties, as well as their relevance for the alloimmune response in vivo. These CD8(+)CD103(+) Tregs are generated within mixed lymphocyte cultures (MLCs) and are elevated by additional transforming growth factor-beta. Interestingly, myeloid dendritic cells are the responsible cell type for induction of CD103(+) Tregs. Allostimulated CD8(+)CD103(+) Tregs display an antigen-experienced effector phenotype with limited effector functions such as cytotoxicity and interferon-gamma production and show a reduced proliferation capacity after restimulation. Beside this anergic phenotype, CD8(+)CD103(+) Tregs are able to suppress alloreactive effector T cells. Through intracellular cytokine staining and transwell assays, we showed that the mechanism of suppression is cytokine independent, but close cell-cell contact is required for suppression.

Regulatory functions of CD8+CD28- T cells in an autoimmune disease model

CD8+ T cell depletion renders CD28-deficient mice susceptible to experimental autoimmune encephalomyelitis (EAE). In addition, CD8-/-CD28-/- double-knockout mice are susceptible to EAE. These findings suggest a role for CD8+ T cells in the resistance of CD28-deficient mice to disease. Adoptive transfer of CD8+CD28- T cells into CD8-/- mice results in significant suppression of disease, while CD8+CD28+ T cells demonstrate no similar effect on the clinical course of EAE in the same recipients. In vitro, CD8+CD28- but not CD8+CD28+ T cells suppress IFN-gamma production of myelin oligodendrocyte glycoprotein-specific CD4+ T cells. This suppression requires cell-to-cell contact and is dependent on the presence of APCs. APCs cocultured with CD8+CD28- T cells become less efficient in inducing a T cell-dependent immune response. Such interaction prevents upregulation of costimulatory molecules by APCs, hence decreasing the delivery of these signals to CD4+ T cells. These are the first data establishing that regulatory CD8+CD28- T cells occur in normal mice and play a critical role in disease resistance in CD28-/- animals.

Cytokine production and expression of leucocyte-differentiation antigens by human mononuclear cells in response to mycobacterium tuberculosis antigens

The aim of this work was to characterize a leucocyte-differentiation antigen or chemokine receptor that allows the identification of type 1 (T helper 1 (Th1), Tc1) and type 2 (Th2, Tc2) lymphocytes in short-term-cultured human peripheral blood mononuclear cells. In addition, we assessed the type of response induced by mycobacterial antigens in tuberculosis patients and healthy contacts. Cells were stimulated with an unfractionated culture filtrate or 30 kDa antigen from Mycobacterium tuberculosis. Then, CD4 and CD8 cell labelling was combined with CD30, CD27, CD28, CD45RA or CD45R0 staining, detection of intracellular interferon-gamma (IFN-gamma) or interleukin-4 (IL-4) and analysis by three-colour flow cytometry. In separate experiments, the expression of different chemokine receptors (CCR1, CCR3, CCR5, CXCR3 and CXCR4) was also studied. We found that none of the cell-surface molecules studied was preferentially expressed by Th1 or Th2 cells. Thus, our results indicate that these lymphocyte subsets cannot be identified in short-term-cultured mononuclear cells on the basis of preferential expression of the cell markers studied, and that it is necessary to look for additional molecules that allow the discrimination of Th1 and Th2 cells.

Costimulation of CD28- T cells through CD3 and beta1-integrins induces a limited Th1 cytokine response

The costimulatory molecule CD28 regulates antigen-specific T-cell proliferation and the synthesis of multiple cytokines. The absence of CD28 on a subset of CD8bright+ T cells suggests that these cells may utilize alternative costimulatory pathways or have a limited cytokine response to presented antigen. We used fibronectin, a ligand for the beta1-integrins alpha4beta1 and alpha5beta1, as an alternate costimulatory ligand to assess the functional phenotype of CD8bright+CD28- T cells. CD25 expression was significantly up-regulated in CD8bright+CD28- T cells by immobilized anti-CD3i with fibronectin. Costimulation with fibronectin also significantly augmented anti-CD3i-induced IFN-gamma production only among CD8bright+CD28- T cells. The CD8bright+CD28- T cells did not produce significant IL-2 and IL-10 even in response to maximal stimulation with phorbol myristate acetate and ionomycin. These data support a costimulatory role for ss1-integrins in CD8bright+CD28- T cells and indicate that CD8bright+ CD28- T cells have a restricted Th1 cytokine repertoire.

Antigen presenting cells integrate opposing signals from CD4+ and CD8+ regulatory T lymphocytes to arbitrate the outcomes of immune responses

An individual's set of polymorphic HLA class II and I molecules is known to select the T cell repertoire in the thymus and to present processed antigenic peptides (pAg) to mature peripheral CD4+ T helper (Th) and CD8+ T cytotoxic (Th) cells in the periphery. This review highlights new studies which address how antigen presenting cells (APC) integrate the responses of cognate Th and T suppressor (Ts) cells to determine the outcome of immune responses. Together with other findings, these studies emphasize that understanding the mechanism of immune processes requires consideration of HLA molecules in the context of the peptides they bind, the antigen presenting cells (APC) that express them and the T lymphocytes that recognize them. The activities of lymphocyte and APC surface structures are becoming integrated into a physiological understanding of the cellular interactions between regulatory and effector T cells with APC.

Combinations of four virostatics applied in rotational sequences induce an exponential VL regression curve, the first part of which is rapidly decreasing to a PCR-undetectable level, while the last part is insensitive to the model. Indications for virostatic and immunotherapeutic reinforcements?

Between 1992 and 1995, we have had five virostatics available: zidovudine (AZT), didanosine (ddI), zalcitabine (ddC) (as retrotranscriptase nucleosidic antagonists, RTNA), acriflavine (ACF), and hydroxy-methyl-ellipticine (HEL), as respectively a DNA synthesis and structure antagonist, and a topoisomerase II inhibitor. Between 1995 and now, we have had ten virostatics the same, plus lamivudine (3TC), stavudine (d4T) as RTNA, and indinavir (IDV), ritonavir (RTV) and saquinavir (SQV) as protease inhibitors. We first conducted a phase I-like study concerning the ratios of the drug numbers in combinations over the numbers available. The optimal model for the study was that of four virostatics selected out of the ten. The four virostatic combinations were applied in short (3 week) sequences, differing each others by drug rotation. The patients were, before treatment, nine at the phase of AIDS, one at the A3 stage. They presented a very rapid decrease of viral load (VL) which became undetectable at PCR, being first below 200 RNA copies/mL, then below 20. We call this condition 'minimum residual disease' as HIV1 persistence is revealed by virus rebounds, reversible, and probably induced by cofactors. The frequency of the latter selection is due to the very frequent (each 3 weeks) VL evaluations. The last part of the VL exponential curve which the minimum residual disease represents, is almost horizontal and quasi insensitive to the powerful virostatic model described above, though no resistance has appeared at the combination or sequence levels. Thus we propose to add phases of: a) reinforcements by virostatics, adding two more ones to the four of the model; and b) treatment complement by active immunotherapy phases: the most adapted immunomodulator is the combination of the peptidic cytokine, tuftsine, and of its antipeptidase, bestatine If they are not available, another interleukine, able to help restoring the AIDS disturbed immunologic system, interleukin 2, could be tried, as it has induced beneficial effects at very small doses by subcutaneous injections.

Age-related changes in blood lymphocyte subsets of Chinese children

BACKGROUND

Flow cytometric analysis of major lymphocyte populations and their subsets reveals age-related changes in the human cellular immune system.

SUBJECTS AND METHODS

Immunophenotypic markers were evaluated in 136 healthy pediatric subjects divided into groups of newborn infants (cord blood), children aged 1 to 2 years, 2 to 5 years, and 6 to 15 years.

RESULTS

The percentage of T cells increased gradually with age and the evolution of the percentage of B and NK cells was found to be variable. The percentage of CD4+ cells remains relatively unchanged from infancy to adolescence, but the percentage of CD8+ T cells was lowest at birth and reached maximal levels in the one to two year-old period. The percentage of naive T cells declined with time, but the percentage of memory T cells increased with age. Similar trends were seen in T-cell receptor alphabeta- and gammadelta-bearing T cells. The percentage of CD 11b+CD8+ T cells increased gradually from birth and reached maximal levels from 6 to 15 years old. The expression of the activation markers CD25 and HLA-DR on CD4+ T cells increased with age. The percentage of CD16+CD56- NK cells declined with age, but the evolution of the percentage of CD 16-CD56+ NK cells was variable. The fraction of B cells that expressed CD5 was high at birth (72.9%) and was highest in one to two year olds (73.1%), then declined steadily over time. The CD23 antigen was expressed on 41.9% of B cells at birth and 68.6% during the first to second year, then declined steadily with age.

CONCLUSION

These data may serve as a reference range for studies of Chinese pediatric subjects.

B7-1, But Not CD28, Is Crucial for the Maintenance of the CD4+ T Cell Responses in Human Leprosy

We used human leprosy as a model to compare patterns of costimulatory molecule expression in respect to the clinical/immunologic spectrum of disease. We found that B7-1, B7-2, and CD28 transcripts dominated in tuberculoid leprosy patients, who have potent T cell responses to Mycobacterium leprae. In contrast, CTLA-4 was more strongly expressed in lesions from lepromatous patients, who manifest specific T cell anergy to the leprosy bacterium. T cell clones from tuberculoid lesions were CD4+CD28+ or CD4+CD28−, and T cell clones from lepromatous lesions were predominantly CD8+CD28−. The M. leprae-specific recall response of CD4+ T cell clones from tuberculoid lesions was blocked by anti-B7-1 mAb, but not by anti-B7-2 mAb or CTLA-Ig. However, anti-CD28 and anti-CTLA-4 mAbs did not block activation of clones from tuberculoid lesions, suggesting that B7-1 may utilize another costimulatory pathway. Peripheral blood T cell responses in the lepromatous form were strongly regulated by CD28 during T cell activation, in contrast to the tuberculoid form. Thus, B7-1 costimulation could play a role in maintaining a strong immune response to the pathogen.

Age-related loss of immunoregulatory function in peripheral blood CD8 T cells

CD8+ T cells from young individuals become inhibitory for the (Staphylococcus aureus + interleukin 2)-induced differentiation of autologous B cells into immunoglobulin secreting cells (ISC) after exposure to pokeweed mitogen (PWM), dimaprit or intracellular cAMP raising agents, such as forskolin or dibutyryl-cAMP. In the present study this immunoregulatory activity was found to be lacking in CD8+ T cells from peripheral blood lymphocytes (PBL) of aged (> 67 years old) subjects. Splenic CD8+ T cells from most individuals examined, including some aged subjects, exhibited this activity. While an age-related decrease in the CD8+ T cell subset, primarily in the virgin CD8+ T cells in PBL, was detected, this decrease was not sufficient to explain a total absence of activity. There was no age-related decrease in cAMP upregulation by forskolin or dimaprit in peripheral blood T cells. However, whereas PWM induced a highly significant increase in mRNA for transforming growth factor-beta (TGF-beta) in T cells from young individuals, no such increase could be detected in T cells from aged subjects. It is suggested that the decrease in immunoregulatory activity in PBL from the elderly may at least in part be due to a decrease in TGF-beta production.

CD28 expression in T cell aging and human longevity

Functional decrements of the immune system have a major contribution to aging and age-related diseases. Here, we further characterize the decline in proportion of CD28-positive T cells previously identified in centenarians. Cohorts of 97 centenarians, 40 subjects aged 70-90 (ELD group), and 40 young adults (under age 40) were phenotyped for T cell surface expression of CD28, CD4, and CD8 antigens. The significant decline in T cells expressing CD28 (p < 10(-4) for comparisons between adults and either ELD or centenarians) affects preferentially the CD8+ subset of T cells. This decline accounts largely for the age-related diminution of T cell responsiveness to mitogenic signals. CD28 expression is modulated in T cell cultures in a growth-related fashion and this modulation is dampened in cultures from centenarians. We propose that the decrease in CD28 expression reflects a compensatory adaptation of the immune system during aging in the face of chronic stimulation.

Primary defect in CD8+ lymphocytes in the antibody deficiency disease (common variable immunodeficiency): abnormalities in intracellular production of interferon-gamma (IFN-gamma) in CD28+ ('cytotoxic') and CD28- ('suppressor') CD8+ subsets

We have measured by flow cytometry the ability of subsets of CD8+CD3+ lymphocytes within mononuclear cell preparations to make intracellular cytokines (IL-2, tumour necrosis factor-alpha (TNF-alpha) and IFN-gamma) on stimulation in vitro with phorbol myristate acetate (PMA) and ionomycin for 16 h. These CD8+ subsets were defined by the presence or absence of CD28 or HLA-DR. Subsets of normal CD8+ cells were compared with cells from the antibody deficiency disease common variable immunodeficiency (CVID). In CVID there was a significant increase in the production of IFN-gamma in the CD8+CD28+ subset ('cytotoxic'). This reflects a shift in this disease towards an excessive Th1 response away from B cell help. Paradoxically, some CVID patients also showed a reduction in IFN-gamma production in the CD8+CD28- subset ('suppressor') which was associated with a failure of these cells to maintain a state of activation after a stimulus in vitro. The B cell problem in this disease is known to be related to a failure of T cell help shown by an inability to produce the antigen-specific CD4+ memory T cells needed for successful B cell maturation. The two pathological CD28 subsets of CD8+ cells we have found in CVID may both be detrimental to a normal CD4-dependent immune response. The CD28- suppressor subset expands and is unable to maintain activation and cytokine secretion, and the CD28+ cytotoxic subset is over-producing the Th1 cytokine IFN-gamma.

HIV type 1 envelope glycoprotein 120 carboxy-terminal peptide-induced human T cell lines selectively suppress heterogeneous proliferative T cell responses to soluble antigens

It has been proposed that the highly conserved human immunodeficiency virus type 1 (HIV-1) envelope gp120 carboxy-terminal sequence, TKAKRRVVEREKR (CT120), may represent a functional mimic of the human leukocyte antigen (HLA) class II DR beta-chain third hypervariable region (HVR3) sequence motif located at position 69-81. Presentation of this potentially pathogenic fragment by HLA class I and/or II molecules, in a manner analogous to the indirect pathway of allorecognition, may induce both widespread cellular activation and also break self-tolerance, resulting in the selective and progressive anti-self HLA class II-directed immune suppression, which is a central feature of HIV-1 infection and the associated acquired immune deficiency syndrome (AIDS). To investigate the functional role of the HIV-1 gp120 C-terminal fragment T cell lines (TCLs) were raised from three healthy HIV-1-seronegative subjects at low risk of HIV-1 exposure, by repeated stimulation with a short synthetic 13-mer CT120 peptide in vitro. Graded concentrations (10[3] to 5 x 10[4]) of CT120 TCLs suppressed the primary 6-day proliferation of autologous PBMCs in response to the soluble antigens tetanus toxoid (TT) and purified protein derivative (PPD). In contrast, CT120 TCLs demonstrated no suppressive effect on 3-day phytohemagglutinin (PHA), concanavalin A (ConA), and pokeweed mitogen (PWM) mitogenic responses. Fractionation of CT120 TCLs into highly purified CD4+ and CD8+ T cell subsets demonstrated that the CD8+ T cell fraction mediated the suppressor effector function. HLA restriction analysis revealed a complex pattern as both anti-HLA class II DR and anti-HLA class I (A, B, C) MAbs inhibited proliferation of oligoclonal CD8+ CT120 TCLs. Strategies aimed at specifically inhibiting such putative immunopathogenic HIV-1-encoded T cell epitopes may be an important consideration for development of future HIV-1 immunotherapy.

Immunity aging. I. The chronic perduration of the thymus acute involution at puberty? Or the participation of the lymphoid organs and cells in fatal physiologic decline?

The author has focused the subject on the perduration of puberty thymus involution as a cause of immunity aging, a term in which he does not include senescence. The decrease between immune reactions against HIV1 at 25 years of age and those at 35 is considerable; the decrease is also indirectly revealed by spontaneous tumor exponentially growing incidence after 40 years in man and its equivalent, 16 months in mice: the immunity parameters indicate a regression correlated with this incidence growth. He regrets the neglect of suppressor cell and anti-idiotype problems by the basic immunologic research. Given the role of cofactors non specifically related to the antigen, such as that CD28 and its ligands, he suggests the interest to approach immunology via the science of chaos and fractals, which would be more appropriate than classical methodology to study highly complex phenomena on which apparently minimal interventions may induce considerable effects.

The last revised "Euro-American classification" of lymphoid leukemias and non-Hodgkin's lymphomas: the same inaccuracies and inconsistencies in a chaotic complexity

After a review of the recent physiologic, cellular genetic and molecular genetic acquisitions, a critical comment of the proposed classification is presented concerning especially a) the inclusion in the so-called "precursor B-lymphoblastic leukemias", which are pre-B neoplasias, of Burkitt's leukemic lymphoma, the cells of which are sIg+, hence B and not pre B; b) the inclusion in the chronic B lymphocytic leukemia of the so-called Galton's "prolymphocytic" leukemia, the cells of which are also sIg+, thus B and not pro B. In fact, the transformed blastoid medium size cells of this leukemia present the markers of the plasmablasts, which are the precursors of the long-lived plasma cells and migrate from the lymphoid tissue T-zone to bone marrow, where they secrete IgD, or G, or E, or to the mucosae, where they secrete IgA. Thus the so called "B-prolymphocytic leukemia" is the leukemic conversion of the (blastoid medium size cell) plasmablast lymphoma. There is in the new classification, a "large cell lymphoma" entity, which makes redundance with the "large cell follicle centre lymphoma". This large cell lymphoma representes a heterogen complex, as it includes the B-immunoblastic lymphoma which is not presented as an entity. As far as T lymphomas are concerned, it is not indicated that the CD8 cells may be CD57 + or - , and CD28 + or -. It could be mentioned that the cytotoxic T-cells are CD8+ C57- CD28+, while the suppressor T-cells are CD8+ CD57+ CD28-.

Will killing the last HIV1 particle cure AIDS patients? II: Second Part. Decrease of viral load and of T-suppressor cells, and increase of the cytotoxic cells, without effect on CD4, after the use of 10 virostatics applied in 3 or 4 drug combinations of different sequences. The time for CD4 immunotherapy?

We reported in the first part of this editorial and in an article AIDS therapy with five HIV1 virostatics applied in two then three, or initially three, or initially four agent combinations, given in 3 week sequences differing from each other due to drug rotation, the contrast between: a) the decrease of viral load, possible below the detectable level, b) the absence of effect on the helper CD4+, the CD8+ C57- cytotoxics and the CD8+ C57+ suppressor cells. We proposed a thesis according to which the HIV1-AIDS complex might have another pathogenic component other than HIV1, ie, a microchimerism graft-versus host reaction (GvH) or an autologous GvH-like reaction. Shifting from five to 10 virostatics owing to the availability of lamivudine or 3TC, stavudine or d4T and three HIV1 protease inhibitors, saquinavir, ritonavir and indinavir, applied according to the same modality, we have enhanced the reduction of viral load, and significantly decreased the CD8+ C57+ suppressor cell counts, and increased those of the CD8+ C57- cytotoxic cells. This result which indirectly shows the role of HIV1 in the increase of suppressor CD8+ cells, hence in the late loss of immune memory and of opportunistic infections, reinforces the thesis of a role, in AIDS pathogenesis, of a latent GvH reaction activated by HIV1 primo-infection, and its evolution from the hyperplastic phase to the hypoplastic one, which, inducing severe immune suppression, is responsible for HIV1 active infection relapse after the so-called latent phase. Hence the proposition we make, of an indication of CD4 modulation with non specific immunotherapy by bestatin, of which we showed the effect in another population of HIV1-AIDS complex patients. Its effect can be potentiated by tuftsin. When the suppressor cell number goes up over that of the cytotoxic one after the HIV1 active infection relapse, interferon gamma could be added, which, by amplifying the CD28 pathway on CD8+ cytotoxics, while suppressor cells lack CD28, which might reestablish a ratio of suppressor over cytotoxic cells nearer to normal. It remains that the role of the five secondarily included agents in the decrease of suppressor cells will only be attributed with certainty and entirely to their virostatic effect, if it is shown that none of them exerts a selective anti-suppressor cell action.

Alterations in levels of CD28-/CD8+ suppressor cell precursor and CD45RO+/CD4+ memory T lymphocytes in the peripheral blood of multiple sclerosis patients

A comprehensive peripheral blood immunophenotype analysis of 16 multiple sclerosis (MS) patients was performed by three-color flow cytometric analysis, and the results were compared with those for age-matched healthy controls. The cell subsets quantified included T cells (CD3+), B cells (CD19+), NK cells (CD56+), CD4+ and CD8+ T cells, cytotoxic (CD28+) and suppressor precursor (CD28-) CD8+ T cells, CD45RA+ and CD45RO+ T cells (CD4+ and CD8+), and CD5+ T and B cells. Analysis of MS patients' peripheral blood revealed essentially normal levels of total T, B, and NK cells. In agreement with results obtained by other investigators, it was found that MS patients had an increased CD4/CD8 ratio, primarily due to a decrease in CD8+ T cells. MS patients were found to have a significantly decreased level of suppressor precursor (CD28-) CD8+ T cells compared with that of controls but to have normal levels of cytotoxic (CD28+) CD8+ T cells. These data indicate that MS patients do not have a general decrease in CD8+ T cells but that they have a specific decrease in the suppressor precursor subset only and normal levels of cytotoxic CD8+ T cells. MS patients also had a significant increase in memory (CD45RO+) CD4+ T cells and displayed a trend towards a decrease in naive (CD45RA+) T cells in the peripheral blood.

Definition of a human suppressor T-cell epitope

The quality of the response produced by regulatory or helper T (Th) cells presently receives much attention because of its possible implications for vaccine development and immunomodulation. Apart from cytokines and so-called costimulatory signals, antigens and the presenting major histocompatibility complex (MHC) molecules may play a role in determining the type of T-cell response generated toward antigens. To examine the role of antigen and/or HLA in control of T-cell subset activation, we have studied a special case, namely CD4+ suppressor T (Ts) cells in leprosy. Mycobacterium leprae-induced Ts cell clones have been previously isolated from peripheral blood and skin lesions of lepromatous leprosy patients and were shown to specifically down-regulate mycobacterium-specific Th cell responses. Despite considerable effort, the antigens recognized by these Ts cells have thus far not been identified. Here we report that all HLA-DR2-restricted CD4+ Ts cell clones derived from a lepromatous leprosy patient recognize an epitope that maps between the amino acid residues 439 and 448 of the mycobacterial hsp65. The peptide was presented to these Ts cells by HLA-DRB1*1503, a recently discovered HLA-DR2 variant. Non-suppressor T-cell clones derived from the same patient recognized antigens other than the hsp65 and were also stimulated by other HLA-DR2 variants. In independent cloning experiments peptide 435-449 and recombinant hsp65 induced exclusively Ts cells in this lepromatous leprosy patient. The Ts clones recognizing this particular epitope were derived from at least seven different progenitors, as they expressed different T-cell receptor alpha and beta chains. Thus, our data indicate that a specific peptide-HLA class II combination may exclusively activate Ts cells.

Z-100, a lipid-arabinomannan extracted from Mycobacterium tuberculosis, improves the resistance of thermally injured mice to herpes virus infections

The effect of Z-100, a lipid-arabinomannan extracted from Mycobacterium tuberculosis strain Aoyama B, was investigated on the resistance of thermally injured mice (TI-mice) to herpes simplex virus type 1 (HSV) infections. The susceptibility of TI mice to infection was about 100 times greater than it was in normal mice (N mice). However, the increased susceptibility of TI mice to infection was effectively counteracted to the levels observed in N mice when treated with Z-100 (10 mg/kg i.p.; 1, 3 and 5 days after thermal injury). Adoptive transfer of burn-associated CD8+ CD11b+ TCR gamma/delta + suppressor T (BAST) cells, prepared from TI mice, increased the susceptibility of N mice to infection by HSV, while the susceptibility of N mice, inoculated with the CD8+ T-cell fraction prepared from Z-100-treated TI mice (ZTC), to infection was not changed. In addition, the suppressor cell activity of BAST cells was not demonstrated when they were assayed in vitro in the presence of anti-IL-4 monoclonal antibody (mAb). BAST cells released IL-4 into their culture fluids without stimulation. The suppressor cell activity of ZTC and IL-4 production by ZTC were minimal. These results suggest that Z-100 may improve the resistance of TI mice to HSV infection through the regulation of BAST cells and/or the release of IL-4 from these cells.

Suppressor T cells: some answers but more questions

Many properties of suppressor T cells and the antigen-binding factors derived from them have evaded molecular genetic definition. Here, Martin Dorf and colleagues discuss recent data in the context of a growing awareness of the molecules and principles involved.

Characterization of suppressor T cell clones derived from a mouse tolerized with conjugates of ovalbumin and monomethoxypolyethylene glycol

The induction of antigen-specific tolerance in mice by conjugates of ovalbumin (OVA) and monomethoxypolyethylene glycol (mPEG) previously had been shown to be associated with the generation of antigen-specific suppressor T (Ts) cells. For the elucidation of the nature of these Ts cells, five nonhybridized OVA-specific Ts cell clones were generated from the spleen cells of a BDF1 mouse which had been immunosuppressed by the tolerogenic conjugate, OVA(mPEG)12. The cloned Ts cells were maintained in vitro by periodic stimulation with OVA and feeder cells and were able to suppress the in vitro antibody production in an OVA-specific and MHC class I (H-2Kd or H-2Dd)-restricted manner. All these Ts cell clones were shown to be Thy1.2+, CD4-, CD5-, CD8+, and to express CD3 and the alpha beta heterodimer of the T cell receptor. The cell-free extracts of these cells contained soluble suppressor factors which could mimic in vitro the suppressive activity of the intact cells. In contrast to cytotoxic T lymphocytes (CTL), none of the cloned Ts cells were endowed with cytolytic activity as revealed in the perforin-mediated microhemolysis and in the 18-hr51Cr release assays. These results demonstrate that (i) OVA-specific Ts cell clones can be generated from mice pretreated with OVA(mPEG)12 by employing conventional T cell culture techniques, and (ii) these Ts cells are functionally different from conventional CD8+ CTL.

Differing lymphokine profiles of functional subsets of human CD4 and CD8 T cell clones

Functional subsets of human T cells were delineated by analyzing patterns of lymphokines produced by clones from individuals with leprosy and by T cell clones of known function. CD4 clones from individuals with strong cell-mediated immunity produced predominantly interferon-gamma, whereas those clones that enhanced antibody formation produced interleukin-4. CD8 cytotoxic T cells secreted interferon-gamma. Interleukin-4 was produced by CD8 T suppressor clones from immunologically unresponsive individuals with leprosy and was found to be necessary for suppression in vitro. Both the classic reciprocal relation between antibody formation and cell-mediated immunity and resistance or susceptibility to certain infections may be explained by T cell subsets differing in patterns of lymphokine production.