Maximal interferon-gamma production and early synthesis of interleukin-2 by CD4+ CDw29- CD45R- p80- human T lymphocytes

Functionally distinct subsets within the T-helper (CD4+) cell population have been described in man, rat and mouse. We have shown previously that the CD4+ 45R- human lymphocytes are producers of IL-2 within 24 hr of polyclonal stimulation and are the major interferon (IFN) producers. The mAbs 4B4 (CDw29) and Leu 8 (p80) are here used together with Leu-18 (CD45R) to characterize the subpopulations of the CD4+ human lymphocytes in more detail. The majority of the CD45R+ cells were CDw29- and the majority of the CDw29+ cells were CD45R-. Most of the CD45R+ cells (78%) were also p80+. A significant number of cells (12%) were CDw29- CD45R-. The predominant subpopulations were defined to be CDw29- CD45R+ p80+ (31%), CDw29+ CD45R- p80- (24%) and CDW29+ CD45R- p80+ (18%). Within the CD4+ CD45R- subpopulation different subsets vary in their capacities to produce IFN and to produce IL-2 within 24 hr after activation. CD4+ CDw29- CD45R- p80- T lymphocytes produced the largest quantities of IFN and IL-2.     

CD4+CD45R+ cells are preferentially activated through the CD2 pathway

CD4 cell subsets, CD4+CD45R+ (CDw29-) cells and CD4+CD45R- (CDw29+) cells, can be differently triggered by various stimuli and possess distinct functions. In the present study, cell activation in CD4+CD45R+ and CD4+CD45R- subsets mediated by CD3-Ti antigen-receptor complex or CD2 molecule were examined by using anti-CD3 antibody or pairs of anti-CD2 antibodies (anti-T11(2) and anti-T11(3) antibodies). The results showed that CD4+CD45R+ cells were preferentially activated through the CD2 pathway, whereas both subsets were equally activated through the CD3-Ti antigen-receptor pathway when a second signal such as monocytes or interleukin 2 was present. The different responsiveness of CD4+CD45R+ and CD4+CD45R- subsets through the CD2 molecule did not appear to be due to differences in the distribution or number of T11(2) and T11(3) determinants. These data suggest that some part of the functional diversity of CD4 cell subsets might be explained by the differences in cell activation through the CD2 molecule.     

Differential effect of cholera toxin on CD45RA+ and CD45RO+ T cells: specific inhibition of cytokine production but not proliferation of human naive T cells

We have studied how cholera toxin (CT) and its non-toxic cell-binding B-subunit (CTB) affect the activation of pure human T cells in an anti-CD3-driven system. CT, as opposed to CTB, strongly suppressed the proliferative responses as well as cytokine production in CD4+ and CD8+ T cells. CT however, had a differential effect on naive and activated/memory T cell subsets. Costimulation through exogenous IL-2 or through CD28 cross-linking rescued the proliferation of CT-treated naive CD45RA+ T cells, but not of activated/memory CD45RO+ cells. IL-2 production and IL-2 receptor expression were markedly reduced by CT in all T cell fractions, i.e. also in CD45RA+ cells which had maintained proliferative responses. However, the proliferative responses of CT-treated CD45RA+ T cells were IL-2-dependent, as shown by blocking experiments using anti-IL-2 antibodies. These results indicate (i) that CTB has no cytostatic effect on human T cells, (ii) that CT affects proliferation and cytokine production by two different signal pathways, and (iii) that CT might interact with a signal pathway generated through or influenced by CD45.     

Human CD4+CD45R0+ and CD4+CD45RA+ T cells synergize in response to alloantigens.

Alloantigens, unlike recall antigens, activate both CD45RA+ (naive) and CD45R0+ (memory) CD4+ cells to the same extent. These T cell subsets may therefore interact with each other in response to alloantigens on transplanted grafts. We have investigated if the ability of activated CD4+CD45RA+ and CD4+CD45R0+ T cells to produce and respond to interleukin 2 (IL2) and IL4 may be involved in this interaction. After activation, both subsets up-regulate their IL2 receptor (IL2R) and IL4R expression, yet IL4 substantially enhanced the proliferation of the CD4+CD45RA+ but not of the CD4+CD45R0+ T cell subset, while IL2 increased the proliferation of CD4+CD45R0+ but not of the CD4+CD45RA+ T cells. Significantly, the CD4+CD45RA+ T cells synthesized two- to threefold more mRNA for IL2 than the CD4+CD45R0+ subset, while the CD4+CD45R0+ T cells synthesized mRNA for IL4 and interferon-gamma exclusively. The addition of IL2 to alloactivated CD4+CD45R0+ T cells further up-regulated their production of all three lymphokine mRNA; in contrast, IL4 induced an increase in mRNA for IL2 in only the alloactivated CD4+CD45RA+ subset. The reciprocity in the ability of both these CD4+ T cells to synthesize and respond to IL2 and IL4 may provide a rationale for the regulation of lymphokine interactions in vivo. Furthermore, the synergy between these subsets in response to alloantigens, which was directly quantitated by co-culturing CD4+CD45RA+ and CD4+CD45R0+ cells together prior to activation, may potentiate the alloreactivity against transplanted grafts in vivo.     

Differential effects of CD28 costimulation upon cytokine production by CD4+ and CD8+ T cells

The impact of CD28 ligation upon CD4+ and CD8+ T lymphocyte proliferation and cytokine production was assessed. Although costimulation increased the proliferative response of both T cell subsets, cytokine production was most markedly increased in the CD4+ subset, as evidenced by a 40-fold increase in interleukin-2 (IL-2), a 14-fold increase in interleukin-3 (IL-3) and 5-fold increases in interferon gamma and GM-colony-stimulating factor (CSF) production. The CD8+ T cell response to CD28 ligation was less marked, maxima being a 5-fold increase in IL-2 production and 2-fold increases in IL-3 and GM-CSF production. Resolution of CD4+ and CD8+ T cells into their CD44lo (na?ve) and CD44hi (memory/effector) subsets revealed that naive CD4+ T cells were the most CD28-responsive subsets. CD28-mediated costimulation promotes distinct differentiation programs in CD4+ versus CD8+ T cells.     

CD45 isoform expression is associated with different susceptibilities of human naive and effector CD4+ T cells to respond to IL-4

Interleukin-4 (IL-4) is the major factor promoting the development of T helper type 2 (Th2) cells from naive precursor T cells. Minute amounts of IL-4 produced by naive T cells seem to be sufficient; however, the molecular mechanisms explaining this efficient utilization of IL-4 are not yet known. Here, we show that human CD4+ CD45RA+ naive T cells, in contrast to CD4+ CD45R0+ effector T cells, show responsiveness to endogenous as well as exogenous IL-4 to proliferate and differentiate towards Th2 cells in vitro. Despite production levels of IL-4 below conventional detection limits, CD45RA+ T cell-derived IL-4 could clearly activate STAT6. Although the expression levels of IL-4R and STAT6 were not different between naive and effector T cells, only naive T cells responded to IL-4 in a STAT6-dependent reporter gene assay. Transfecting a trans-dominant negative form of STAT6 abrogated IL-4-induced proliferation in CD45RA+ cells. A significantly higher protein tyrosine phosphatase (PTPase) activity was detected in CD45R0+ T cells as compared to CD45RA+ T cells. Cross-linking CD45 potently reduced PTPase activity in CD45R0+ T cells and restored their ability to proliferate in response to IL-4. Thus, CD45 PTPase activity contributes to the susceptibility of naive and memory T cells to respond to IL-4.     

Two subsets of human CD4+ T helper cells differing in kinetics and capacities to produce interleukin 2 and interferon-gamma can be defined by the Leu-18 and UCHL1 monoclonal antibodies

Human CD4+ T helper cells were separated into CD4+45R+ and CD4+45R- cells. When stimulated with the polyclonal activator staphylococcal enterotoxin A in the presence of autologous monocytes, these two subsets exhibited a striking difference in production of interleukin 2 (IL2) and interferon-gamma (IFN-gamma). While the CD4+45R- subset produced maximal amounts of IL2 within 24 h and IFN-gamma within 72 h, the CD4+45R+ subset produced no IL2 within 24 h and merely marginal amounts of IFN-gamma as assayed after 24 to 96 h. This discrepancy between the subsets was found when the cells were stimulated by other accessory cell-dependent activators and by the accessory-independent combination of the calcium ionophore A23187 and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate as well. The inability of the CD4+45R+ cells to produce IL2 during the first day of culture was not due to any modulation of either the CD4 or the CD45R antigens, as purified CD4+45R+ cells obtained by negative panning selection with the reciprocal UCHL1 monoclonal antibody responded in a similar manner as the positively selected sorted CD4+45R+ cells. Analysis of the kinetics of IL2 production by the two T helper cell subsets clearly demonstrated that the IL2 recorded after 1 day of culture was entirely produced by the CD4+45R- cells, whereas the CD4+45R+ cells produced IL2 during and after the second day of culture. This discrepancy in kinetics was not due to an increased absorption of IL2 by the CD4+45R+ cells during the first day of culture.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibitory effect of IL-4 on the sepharose-CD3-induced proliferation of the CD4CD45RO human T cell subset

CD45R monoclonal antibodies are able to distinguish two different subsets of the CD4 human T cells. This phenotypic split is accompanied by functional diversity. In this report we have analyzed the capabilities of CD45R subsets of CD4 human T cells to use interleukin 2 (IL-2) and IL-4 as growth factors. We have found that both cell subsets are able to proliferate after stimulation with Sepharose-CD3 in the presence of externally added IL-2 or IL-4. However, the response to IL-4 of CD4CD45RO cells was comparatively lower than the response of CD4CD45RA cells. Both cell subsets showed a good response to Sepharose-CD3 plus adherent cells (AC), but when IL-4 was present in the culture only the CD4CD45RA cells showed an enhancement in the Sepharose-CD3-induced proliferation, while proliferation of the CD4CD45RO T cell subset was inhibited. Similar effects were seen, however, in the response to CD4CD45RA or CD4CD45RO cells to Sepharose-CD3 plus IL-2. Although the precise mechanism of the inhibitory effect of IL-4 is not known, the results obtained suggest that IL-4 could interfere in some way with the signalling of IL-2 to the proliferation of the CD4CD45RO T cell subset.     

Immunoregulatory CD4+ CD45R+ suppressor/inducer T lymphocyte subsets and impaired cell-mediated immunity in patients with Down''s syndrome.

The monoclonal antibodies 2H4 and 4B4 allow CD4+ and CD8+ T lymphocytes to be subdivided into CD45R+ and CDW29+ functional subpopulations. The CD4+ CD45R+ lymphocytes are designated as suppressor/inducer and CD4+ CDW29+ as helper/inducer subsets. Peripheral blood lymphocytes from 19 patients with Down's syndrome and 19 age- and sex-matched normal controls were analysed for the CD45R+ and CDW29+ subsets from the CD4+ and CD8+ T lymphocytes. The percentage of CD4+ CD45R+ cells (suppressor inducer) was markedly increased and of CD4+ CDW29+ cells (helper/inducer) decreased in all patients with Down's syndrome. In contract, the percentage of CD8+ CD45R+ and CD8+ CDW29+ subsets showed no major differences between patients with Down's syndrome and normal controls. Moreover, an alteration in the CD4+ and CD45R+ and CD4+ CDW29+ T cell subsets was accompanied by a markedly reduced proliferative response to phytohaemagglutinin and concanavalin A stimulation of the CD4+ T lymphocytes. Thus, a deficiency exists in patients with Down's syndrome in the CD4+ CDW29+ helper/inducer T cell subset which may contribute to their impaired cell-mediated immunity.     

Impairment of CD3-dependent and CD3-independent activation pathways in CD4+ and in CD8+ T cells from old CBA/RIJ mice

Stimulation of T cells from old mice with anti-CD3 antibodies resulted in a high variability of proliferative responses, which were 2- to 8-fold lower than the responses by T cells from young mice, even in the presence of exogenous rIL-2. Moreover, the CD4+ T cells from these old mice displayed a diminished capacity to produce IL-2 in response to anti-CD3. A partial explanation was found in the observation that T cells from the majority of old mice displayed a diminished expression of CD3 of variable intensity. However, after stimulation of the T cells with the combination of phorbol-12-myristate-13-acetate (PMA) and ionomycin to bypass CD3, 3 out of 6 old mice still exhibited 2-fold lower proliferative responses than T cells from young mice; IL-2 production by the CD4+ T cells was lower in all old mice tested. Comparison of CD4+ T cells and CD8+ T cells from old mice revealed a defective PMA/ionomycin response in both subsets, although this defect seemed more pronounced in CD4+ T cells when compared with the young counterparts. The diminished response of CD8+ T cells was accompanied by a diminished expression of the IL-2R alpha-chain. In contrast, old CD4+ T cells expressed rather higher levels of IL-2R alpha-chain than young CD4+ T cells. Altogether, multiple defects which are not necessarily the same in CD4+ and CD8+ T cells are responsible for defective T cell responses in old mice.     

Activation of human NK cells by plasmacytoid dendritic cells and its modulation by CD4+ T helper cells and CD4+ CD25hi T regulatory cells

Plasmacytoid dendritic cells (pDC) represent a specialized cell population that produce type I interferon (IFN) in response to virus. Although type I IFN is a natural killer (NK) cell modulator, a direct role for pDC in coordinating NK cell functions has not yet been elucidated in detail, especially in humans. Here we report that human pDC, following engagement of Toll-like receptor (TLR) 9, not only activate autologous NK cells, as indicated by the induction of CD69 expression, but also enhance their effector functions, especially cytotoxicity. Moreover, they can induce selective proliferation of CD56bright CD16- NK cells. This activity can be strongly augmented by the addition of autologous CD4+ CD25- T helper cells in an IL-2-dependent fashion. Strikingly, CD4+ CD25hi T regulatory (Treg) cells completely abrogate this IL-2-dependent proliferation of NK cells, while they are not able to influence NK cell activation or proliferation solely induced by pDC. Our data show that TLR9-engaged pDC represent a critical stimulus for human NK cells and that CD4+ Th cells and CD4+ CD25hi Treg cells play an important role in modulating human NK cell responses.     

Similar co-stimulation requirements of CD4+ and CD8+ primary T helper cells: role of IL-1 and IL-6 in inducing IL-2 secretion and subsequent proliferation.

Primary murine CD4+ and CD8+ T helper (Th) cells provide help for various immune responses by secreting lymphokines which activate effector cells. The purpose of the present study was to investigate the co-stimulatory signals that, together with T cell receptor (TCR) cross-linking, induce phenotypically distinct primary Th cells to secrete IL-2 and proliferate. We isolated highly purified populations of primary CD4+ or CD8+ T cells and stimulated them in vitro with platebound anti-CD3 mAb. TCR cross-linking by anti-CD3 mAb induced both IL-2 receptor expression and responsiveness to exogenous IL-2, but was not sufficient to induce either IL-2 secretion or T cell proliferation. Rather, for both CD4+ and CD8+ primary Th cells, IL-2 secretion and proliferation required both TCR cross-linking and antigen presenting cell (APC)-derived co-stimulatory signals. Based on G-10 adherence and sensitivity to gamma-irradiation, the APC populations able to induce primary CD4+ Th cells and primary CD8+ Th cells to secrete IL-2 were indistinguishable. In addition, we found that either IL-1 or IL-6 could replace the requirement for APC-derived co-stimulatory signals for IL-2 secretion and proliferation by both primary CD4+ Th cells and primary CD8+ Th cells. Thus, the present study has examined and compared the co-stimulatory requirements of rigorously purified subsets of IL-2-secreting primary CD4+ and primary CD8+ T cells.(ABSTRACT TRUNCATED AT 250 WORDS)     

CD45R CD4 T cell subset-reconstituted nude rats: subset-dependent survival of recipients and bi-directional isoform switching.

High and low molecular weight variants (CD45R) of the leukocyte common antigen (CD45) divide CD4 T helper cells into subpopulations which display distinct characteristics. In vitro and in vivo evidence suggested that the presence of the high molecular weight splice variants CD45RA or CD45RB distinguished naive CD4 T cells from memory T cells which underwent an irreversible switch to the low molecular weight isoform as a consequence of antigen encounter. In the rat monoclonal antibody MRC OX22 identifies an epitope on the CD45RB molecule. We investigated this proposed differentiation pathway by reconstituting athymic nude rats with highly purified OX22+ or OX22- CD4 T lymphocyte subsets obtained from the thoracic duct (TDL) of euthymic, congenic, allotype-marked donors. Injection of CD4+CD45RB- (45R-) cells ensured long-term survival of nude recipients; recipients of CD4+CD45R+ (45R+) cells died within 2-3 months of injection. Early after transfer (3-4 weeks) the progeny of both 45R+ and 45R- TDL were uniformly 45R-. With time (by 2 months) progeny of both parental types expressed the high molecular weight CD45RB isoform. Nude recipients of 45R- TDL always generated progeny a proportion of which bore the 45R+ phenotype; 3 months to 2 years post-injection, 30%-50% of the donor-derived CD4 T cells were 45R+, 45R- progeny isolated from primary recipients of either 45R- or 45R+ cells transferred into secondary nude recipients induced skin allograft rejection with equal effectiveness and also generated 45R+ offspring. The results indicated that CD4 T cell subsets switched between CD45R isoforms and that the change between high and low molecular weight expression was bi-directional. The splice variants apparently are not lineage or maturation markers, but rather identify CD4 T cells that exist transiently in different functional states.     

Purified Human T Cells Stimulated with Cross-Linked Anti-CD3 Monoclonal Antibody OKT3: rIL-1 is a Co-Stimulatory Factor for CD4+ CD29+ CD45RA− T Cells

Accessory cells (AC) are believed to play two major roles in T-cell activation: they cross-link certain stimuli such as monoclonal antibodies, and they provide needed cytokines. To differentiate between these roles, we cross-linked OKT3 on highly purified T cells by means of Fc-specific goat anti-mouse IgG-coated polystyrene beads and studied T-cell activation after exogenously added cytokines. Following addition of AC, rIL-2, or rIL-1, CD25 was up-regulated, and the cells proliferated and became cytotoxic. Both CD4+ and CD8+ cells were activated in the presence of AC or rIL-2. In contrast, only CD4+CD29+CD45RA- cells responded in the presence of rIL-1. Anti-IL-2R p55 (anti-TAC) monoclonal antibody inhibited the proliferative response supported by rIL-2 or rIL-1. To inhibit proliferation of cells stimulated in the presence of AC, anti-TAC needed to be supplemented with anti-IL-6 antibodies, or to be added in a 10-fold higher concentration. Cultures with AC produced larger amounts of IL-2 than those supplemented with rIL-1. Only AC-containing cultures also produced detectable amounts of IL-6. These findings combined with the observation that none of 2000 purified T cells counted in each of six independent experiments expressed MHC class II antigens strongly suggest that rIL-1 can activate T cells directly, rather than indirectly by potentiating the function of contaminating AC.     

Age-related increase in the fraction of CD27-CD4+ T cells and IL-4 production as a feature of CD4+ T cell differentiation in vivo.

The influence of ageing on phenotype and function of CD4+ T cells was studied by comparing young (19-28 years of age) and aged (75-84 years of age) donors that were selected using the SENIEUR protocol to exclude underlying disease. An age-related increase was observed in the relative number of memory cells, not only on the basis of a decreased CD45RA and increased CD45RO expression, but also on the basis of a decrease in the fraction of CD27+CD4+ T cells. Our observation that the absolute number of CD45RO+CD4+ T cells was increased, while absolute numbers of CD27-CD4+ T cells remained unchanged in aged donors, indicates that the latter subset does not merely reflect the size of the CD45RO+CD4+ T cell pool. The increased fraction of memory cells in the aged was functionally reflected in an increased IL-4 production and T cell proliferation, when cells were activated with the combination of anti-CD2 and anti-CD28, whereas IL-2 production was comparable between both groups. No differences were observed with respect to proliferative T cell responses or IL-2 production using plate-bound anti-CD3 or phytohaemagglutinin (PHA). The observation that IL-4 production correlated with the fraction of memory cells in young donors but not in aged donors suggests different functional characteristics of this subset in aged donors.     

IL-6 produced by type I IFN DC controls IFN-gamma production by regulating the suppressive effect of CD4+ CD25+ regulatory T cells

The dendritic cell family is composed of different subsets differentially governing the immune response. Type I interferon (IFN) dendritic cells (DC) are endowed with the ability to trigger both Th1 and Th2 type responses. In view of the pivotal role of regulatory T cells in limiting the effectiveness of effector cells, we analyzed the interactions between these cells and type I IFN DC. DC were generated from monocytes in the presence of IFN-beta and interleukin (IL)-3 (DCI3) or granulocyte macrophage-colony-stimulating factor and IL-4 (DCG4) and activated by poly(I:C). Despite the release of lower amounts of IL-12 after maturation, DCI3 were able to induce a higher IFN-gamma production by T lymphocytes during the mixed leucocyte reaction (MLR) as compared with DCG4. mRNA analysis disclosed that DCI3 overtranscribed the IL-6 gene and secreted high amounts of the protein. Neutralization of IL-6 revealed that this cytokine specifically contributed to the IFN-gamma release induced by DCI3. Finally, depletion of CD25+ T cells before the MLR identified these cells as a target for IL-6. We conclude that DCI3 are endowed with the property of regulating the suppressive effect of regulatory T cells through high IL-6 production. This novel mechanism of T cell control is relevant for the use of DCI3 in vaccination strategies.     

Inhibition of human T lymphocyte proliferation and cytokine production by 1,25-dihydroxyvitamin D3. Differential effects on CD45RA+ and CD45R0+ cells.

1,25-dihydroxyvitamin D3 (1,25-(OH)2 D3), the biologically active form of vitamin D3, has been shown to modulate lymphocyte functions in vitro. These effects are exerted through binding to specific receptors that are expressed in activated, but not in resting lymphocytes. 1,25-(OH)2 D3 inhibits lymphocyte proliferation, immunoglobulin production and the release of cytokines including interleukin-2 (IL-2) and interferon gamma (IFN gamma) by mitogen driven blood mononuclear cells (MNC). A distinction between CD45RA+ and CD45R0+ subsets of T cells has, however, proven extremely relevant in terms of immunoactivation and immunopathology. The present study was undertaken to evaluate effects of 1,25-(OH)2 D3 on proliferation and cytokine production by purified CD45RA+ and CD45R0+ T cells. 1,25-(OH)2 D3 caused a dose- and time-dependent reduction in phytohemagglutinin-(PHA) and poke-weed mitogen (PWM)-driven proliferation of purified CD45R0+ T cells. In contrast, proliferation of the CD45RA+ subset was unaffected by this treatment. Comparable levels of lymphotoxin (LT), IFN gamma and IL-2 were obtained in cultures of both subsets. 1,25-(OH)2 D3 reduced these levels, but the suppressive effect of the hormone was delayed in cultures of CD45RA+ T cells. The results suggest that the CD45R0+ subset is relatively more sensitive than CD45RA+ subset to the inhibitory effects of 1,25-(OH)2 D3. This finding may be of pharmacological interest, because the CD45R0+ subset plays a key role in immune activation and because these cells have been associated with the pathogenesis of autoimmune diseases such as rheumatoid arthritis and multiple sclerosis.     

Impaired proliferative capacity and abnormal cytokine profile of naive and memory CD4 T cells from HIV-seropositive patients.

Purified naive and memory CD4 T cells from healthy donors, HIV+ asymptomatic carriers and AIDS patients were examined for their proliferative activity and their pattern of cytokine secretion (IL-4, IL-6, interferon-gamma (IFN-gamma) and tumour necrosis factor-alpha (TNF-alpha)) upon stimulation with phytohaemagglutinin (PHA), phorbol myristate acetate (PMA) and cross-linked anti-CD3 MoAb, in the presence of recombinant IL-2 (rIL-2). We found a decrease in the proliferative capacity of naive CD4 T cells following stimulation with PHA and PMA, and a sharp decline in this response upon cross-linked anti-CD3 stimulation in both subsets, although it predominated in the naive subpopulation. In AIDS patients, less pronounced impairment of thymidine uptake by the naive subset was found upon PHA and cross-linked anti-CD3 MoAb stimulation. In addition, an altered secretion pattern of the different cytokines was observed, consisting of abnormal secretion of IL-6 by both naive and memory cells, an abnormal pattern of IFN-gamma secretion and frequent loss of detectable IL-4 production by HIV patients. These abnormalities were even more pronounced in AIDS patients than in the asymptomatic carriers. Overall, our results extend previous reports indicating functional impairment of memory CD4 subsets in HIV+ subjects by showing that this impairment involves naive CD4 T cells.     

ICAM-1 costimulation induces IL-2 but inhibits IL-10 production in superantigen-activated human CD4+ T cells.

We have previously reported that costimulatory pathways including B7-CD28 and lymphocyte function-associated antigen-3 (LFA-3)-CD2 shape distinct activation profiles in human CD4+ T cells. We now show that superantigen (SAg), in combination with intracellular adhesion molecule-1 (ICAM-1) costimulation drives a proliferative response accompanied by high levels of interleukin-2 (IL-2) and moderate levels of interferon-gamma (IFN-gamma) and tumour necrosis factor (TNF). This response profile differs from that observed in B7 or LFA-3 costimulated T cells because our previous results showed that B7-CD28 costimulation was accompanied by high levels of IL-2, IFN-gamma and TNF, whereas LFA-3 was a potent inducer of IFN-gamma and TNF, but had little influence on IL-2 production. The ICAM-1-induced IL-2 production could efficiently be abrogated with monoclonal antibody (mAb) against ICAM-1 or LFA-1, showing that the activation is dependent of a functional ICAM-1-LFA-1 pathway. SAg-induced IL-2, IFN-gamma and TNF were detected in both CD4+ and CD8+ T cells, whereas production of IL-10 was restricted to CD4+ T cells. A major finding in the present study was that ICAM-1 costimulation strongly inhibits IL-10 production in CD4+ T cells. Our data demonstrate that ICAM-1 costimulation is sufficient to induce large amounts of IL-2. The presence of ICAM-1 results in suppression of IL-10 production in T helper (Th) cells, which may favour the development of Th1 and not Th2 T cells.     

Clonal analysis of CD4 mediated accessory function on the effector activity of human CD4+ T cell subsets

Background: It has been reported for the peripheral T cell repertoire that CD4 molecules may enhance adhesion between T cells and antigen presenting cells and, through their physical association with T cell antigen receptors, contribute to signal transduction. Objective: The aims of this study were to determine if the modulation of CD4 molecules had differential effects on T cell recognition, antigen induced cytokine (IL-4 and IFNγ), release and the induction of specific anergy for human TH-0, TH-1 and TH-2 cells. Methods: A panel of anti-CD4 antibodies was examined for its ability to modulate T cell proliferation, cytokine production and tolerance induction in house dust mite (TH-0 and TH-2) and influenza haemagglutinin (TH-1) specific human CD4+ T cell clones all restricted by DRB1^*1101 and isolated from dust mite allergic individuals. Results: We observed that anti-CD4 antibodies may inhibit or enhance antigen mediated T cell proliferation, which may reflect the differential requirements of T cells for selective functions of CD4. Furthermore, IFNγ and IL-4 production was differentially modulated depending on the specificity of the anti-CD4 antibody and the clone of T cells. However, pretreatment of T cells with anti-CD4 antibody alone neither induced nor enhanced the susceptibility of T cells to peptide mediated anergy. Conclusion: Antigen recognition by different subsets of human CD4+ T cells has differential requirements on CD4, whereas the induction of specific anergy appeared to be independent of the functions of CD4 molecules. Antigen induced IFNγ production was more susceptible than IL-4 to the inhibitory effects of anti-CD4 antibodies. Furthermore, it appeared that certain anti-CD4 antibodies can dissociate antigen induced IFNγ and IL-4 production, and may downregulate IFNγ synthesis without inhibiting antigen dependent proliferation.