IL-17 Induction by ArtinM is Due to Stimulation of IL-23 and IL-1 Release and/or Interaction with CD3 in CD4+ T Cells

ArtinM is a D-mannose-binding lectin extracted from the seeds of Artocarpus heterophyllus that interacts with TLR2 N-glycans and activates antigen-presenting cells (APCs), as manifested by IL-12 production. In vivo ArtinM administration induces Th1 immunity and confers protection against infection with several intracellular pathogens. In the murine model of Candida albicans infection, it was verified that, in addition to Th1, ArtinM induces Th17 immunity manifested by high IL-17 levels in the treated animals. Herein, we investigated the mechanisms accounting for the ArtinM-induced IL-17 production. We found that ArtinM stimulates the IL-17 production by spleen cells in BALB/c or C57BL/6 mice, a response that was significantly reduced in the absence of IL-23, MyD88, or IL-1R. Furthermore, we showed that ArtinM directly induced the IL-23 mRNA expression and the IL-1 production by macrophages. Consistently, in cell suspensions depleted of macrophages, the IL-17 production stimulated by ArtinM was reduced by 53% and the exogenous IL-23 acted synergistically with ArtinM in promoting IL-17 production by spleen cell suspensions. We verified that the absence of IL-23, IL-1R, or MyD88 inhibited, but did not block, the IL-17 production by ArtinM-stimulated spleen cells. Therefore, we investigated whether ArtinM exerts a direct effect on CD4⁺ T cells in promoting IL-17 production. Indeed, spleen cell suspensions depleted of CD4⁺ T cells responded to ArtinM with very low levels of IL-17 release. Likewise, isolated CD4⁺ T cells under ArtinM stimulus augmented the expression of TGF-β mRNA and released high levels of IL-17. Considering the observed synergism between IL-23 and ArtinM, we used cells from IL-23 KO mice to assess the direct effect of lectin on CD4⁺ T cells. We verified that ArtinM increased the IL-17 production significantly, a response that was inhibited when the CD4⁺ T cells were pre-incubated with anti-CD3 antibody. In conclusion, ArtinM stimulates the production of IL-17 by CD4⁺ T cells in two major ways: (I) through the induction of IL-23 and IL-1 by APCs and (II) through the direct interaction with CD3 on the CD4⁺ T cells. This study contributes to elucidation of mechanisms accounting for the property of ArtinM in inducing Th17 immunity and opens new perspectives in designing strategies for modulating immunity by using carbohydrate recognition agents.     

Neutrophils Contribute to the Protection Conferred by ArtinM against Intracellular Pathogens: A Study on Leishmania major

ArtinM, a D-mannose binding lectin from Artocarpus heterophyllus, has immunomodulatory activities through its interaction with N-glycans of immune cells, culminating with the establishment of T helper type 1 (Th1) immunity. This interaction protects mice against intracellular pathogens, including Leishmania major and Leishmania amazonensis. ArtinM induces neutrophils activation, which is known to account for both resistance to pathogens and host tissue injury. Although exacerbated inflammation was not observed in ArtinM-treated animals, assessment of neutrophil responses to ArtinM is required to envisage its possible application to design a novel immunomodulatory agent based on carbohydrate recognition. Herein, we focus on the mechanisms through which neutrophils contribute to ArtinM-induced protection against Leishmania, without exacerbating inflammation. For this purpose, human neutrophils treated with ArtinM and infected with Leishmania major were analyzed together with untreated and uninfected controls, based on their ability to eliminate the parasite, release cytokines, degranulate, produce reactive oxygen species (ROS), form neutrophil extracellular traps (NETs) and change life span. We demonstrate that ArtinM-stimulated neutrophils enhanced L. major clearance and at least duplicated tumor necrosis factor (TNF) and interleukin-1beta (IL-1β) release; otherwise, transforming growth factor-beta (TGF-β) production was reduced by half. Furthermore, ROS production and cell degranulation were augmented. The life span of ArtinM-stimulated neutrophils decreased and they did not form NETs when infected with L. major. We postulate that the enhanced leishmanicidal ability of ArtinM-stimulated neutrophils is due to augmented release of inflammatory cytokines, ROS production, and cell degranulation, whereas host tissue integrity is favored by their shortened life span and the absence of NET formation. Our results reinforce the idea that ArtinM may be considered an appropriate molecular template for the construction of an efficient anti-infective agent.     

Plant lectin,ATF1011, on the tumor cell surface augments tumor-specific immunity through activation of T cells specific for the lectin

Summary The possibility that a plant lectin as a carrier protein would specifically activate T cells, resulting in the augmentation of antitumor immunity was investigated. ATF1011, a nonmitogenic lectin for T cells purified from Aloe arborescens Mill, bound equally to normal and tumor cells. ATF1011 binding on the MM102 tumor cell surfaces augmented anti-trinitrophenyl (TNP) antibody production of murine splenocytes when the mice were primarily immunized with TNP-conjugated MM102 tumor cells. The alloreactive cytotoxic T cell response was also augmented by allostimulator cells binding ATF1011 on the cell surfaces. These augmented responses may be assumed to be mediated by the activation of helper T cells recognizing ATF1011 as a carrier protein. Killer T cells were induced against ATF1011 antigen in the H-2 restricted manner using syngeneic stimulator cells bearing ATF1011 on the cell surfaces. When this lectin was administered intralesionally into the tumors, induction of cytotoxic effector cells was demonstrated. These results suggest that intralesionally administered ATF1011 binds to the tumor cell membrane and activates T cells specific for this carrier lectin in situ, which results in the augmented induction of systemic antitumor immunity.     

The Lectin ArtinM Induces Recruitment of Rat Mast Cells from the Bone Marrow to the Peritoneal Cavity

Background

The D-mannose binding lectin ArtinM is known to recruit neutrophils, to degranulate mast cells and may have potential therapeutic applications. However, the effect of ArtinM on mast cell recruitment has not been investigated.

Methodology

Male Wistar rats were injected i.p. with ArtinM or ConA (control). The ability of the lectin to degranulate peritoneal and mesenteric mast cells was examined. Recruitment of mast cells to the peritoneal cavity and mesentery after ArtinM injection was examined with or without depletion of peritoneal mast cells by distilled water.

Results

ArtinM degranulated both peritoneal and mesentery mast cells in vitro. Three days after i.p. injection of the lectin there were reduced numbers of mast cells in the peritoneal lavage, while at 7 days post injection of ArtinM, the number of peritoneal mast cells was close to control values. Since immature mast cells are recruited from the bone marrow, the effect of the lectin on bone marrow mast cells was examined. Injection of ArtinM resulted in an increased number of mast cells in the bone marrow. To determine if degranulation of mast cells in the peritoneal cavity was required for the increase in bone marrow mast cells, the peritoneal cavity was depleted of mast cells with ultrapure water. Exposure to ArtinM increased the number of mast cells in the bone marrow of rats depleted of peritoneal mast cells.

Conclusions

The ArtinM induced recruitment of mast cells from the bone marrow to the peritoneal cavity may partially explain the therapeutic actions of ArtinM.     

Specific tumor memory induced by polyethylene-glycol-modified interleukin-2 requires both helper and cytotoxic T cells

Local polyethylene-glycol (PEG)-modified interleukin-2 (IL-2) immunotherapy of the guinea pig Line 10 (L10) tumor was previously demonstrated to evoke long-lasting systemic immunity after cure of the tumor and metastases. T cells, most likely the helper T cell subpopulation, were demonstrated to be crucial to the antitumor effects. Here we show that systemic immunity is induced within 7 days after the start of PEG-IL-2 therapy, indicating a rapid systemic priming of L10-specific T cells. No in vitro cytotoxic activity was detected in cell suspensions obtained from the primary tumor site, the regional lymph node or the spleen when isolated during (days 21 and 28) intratumoral treatment with 200 000 IU PEG-IL-2. These data confirm our carlier results obtained with 60 000 IU PEG-IL-2. Moreover, no cytolytic activity was observed in the chromium-release assay after in vitro restimulation with irradiated tumor cells. Specific L10 immunity can be transferred using spleen cell suspensions. Depletion of such a suspension of helper T cells resulted in rejection of the primary tumor in two out of four animals, but all the guinea pigs developed lymph node metastases. Removal of the cytotoxic/suppressor phenotype caused rejection of the dermal tumor in four of eight guinea pigs, but the capacity to prevent lymph node metastases was retained in all animals. Thus, depletion of either subtype reduces, but does not abrogate, the capacity to transfer L10 immunity with spleen cells. In conclusion, our data suggest that tumor cell killing through direct T cell cytotoxicity is not the main mode of action in PEG-IL-2-induced L10 tumor regression, PEG-IL-2 therapy induces early systemic immunity, resulting in rejection of a distant tumor, and the transfer of this immunity depends mainly on the presence of helper T cells, although cytotoxic T cells may also play a role.     

Spleen cells from athymic mice are ineffective stimulator cells for cytotoxic responses in microcultures and in vivo

The stimulator cells for the activation of cytotoxic T lymphocyte (CTL) precursor cells were studied in vivo and in microculture systems with limiting concentrations of helper factor (interleukin-2). We found in both cases that mixtures of irradiated spleen cells from athymic and euthymic donors of different haplotypes activated CTL responses preferentially against alloantigens which were carried by the euthymic donors. This applied also if athymic and euthymic donors shared parts of the H-2 gene complex. Stimulator cells from athymic and euthymic donors activated, on the other hand, equally strong responses in microcultures which were supplemented with additional helper factor or in conventional macrocultures. This and direct cell mixing experiments showed that the ineffective stimulation by the nude spleen cells in vivo and under conditions of limiting helper factor was not mediated by active suppression. Our experiments are therefore best explained by the assumption that cytotoxic responses under conditions of limiting helper factor require a close proximity between CTL precursor cells and helper T cells. This proximity may be most efficiently provided by the receptors of the CTL precursor cells when helper T cells serve as stimulator cells. Lymph node cells were consistently inferior to spleen cells as stimulator cells, and the nylon wool nonadherent fraction of spleen cells was on the average also inferior to unfractionated spleen cells, indicating that the stimulator T cells belong to a spleen seeking and partly nylon wool adherent T-cell subpopulation or require an additional cell type for optimal stimulation.     

The immunomodulatory effect of plant lectins: a review with emphasis on ArtinM properties

Advances in the glycobiology and immunology fields have provided many insights into the role of carbohydrate-protein interactions in the immune system. We aim to present a comprehensive review of the effects that some plant lectins exert as immunomodulatory agents, showing that they are able to positively modify the immune response to certain pathological conditions, such as cancer and infections. The present review comprises four main themes: (1) an overview of plant lectins that exert immunomodulatory effects and the mechanisms accounting for these activities; (2) general characteristics of the immunomodulatory lectin ArtinM from the seeds of Artocarpus heterophyllus; (3) activation of innate immunity cells by ArtinM and consequent induction of Th1 immunity; (4) resistance conferred by ArtinM administration in infections with intracellular pathogens, such as Leishmania (Leishmania) major, Leishmania (Leishmania) amazonensis, and Paracoccidioides brasiliensis. We believe that this review will be a valuable resource for more studies in this relatively neglected area of research, which has the potential to reveal carbohydrate targets for novel prophylactic and therapeutic strategies.     

T cell control of the antibody response to the T-independent antigen, DAGG-Ficoll

C57BL/6J nu/nu mice respond to the type 2 TI antigen DAGG-Ficoll, but not to the TD antigen SRC. A comparable difference can also be seen in vitro, but only at high spleen cell density and in the presence of selected batches of FBS. At low spleen cell density and in the absence of FBS, the DAGG-Ficoll-induced B cell response is strictly dependent on soluble helper factors or cloned specific helper T cells. The B cell response so induced requires that the T cell-depleted spleen cells be compatible in the I-A subregion of the H-2 complex. These helper factors, induced by antigen in an I-A-restricted T cell-macrophage interaction, provide helper for T cell-depleted spleen cells irrespective of their H-2 haplotype. Under conventional culture conditions, the stringent requirement for helper factors in the in vitro response to DAGG-Ficoll is obscured by FBS. In vitro culture of low numbers of spleen cells, in serum-free medium instead of FBS, provides a sensitive assay for helper factors. We have compared the helper activity for a B cell response to SRC or DAGG-Ficoll as provided by antigen-induced supernatants of various individual EA-specific T cell clones. There was a remarkable and consistent heterogeneity among individual T cell clones: their helper activity in the response to TI and TD antigens did not correlate, nor was there any correlation between helper activity and antigen-induced TCGF (interleukin 2) activity.     

MLC-derived human helper factor(s) that promote B cell differentiation: induction, functional characterization, and role of Ia antigens

Utilizing a PFC assay to quantitate the polyclonal activation of human peripheral blood B lymphocytes, we have investigated the induction and functional activity of MLC-derived human helper factor(s). Our data demonstrate that highly purified responder T cells, but not B or null cells, are required for the elaboration of MLC helper factor(s) that trigger the in vitro differentiation of B lymphocytes into PFC. Helper factor can trigger B cell maturation in the absence of helper T cells, since complement- (C) mediated lysis of the small (less than 5%) fraction of T cells present in anti-F(ab)2 immunoabsorbent column purified B cell population eliminates the PWM induced, but not the helper factor-induced PFC response. Responder T cells required for helper factor production do not bear surface membrane Ia, since alpha p23,30 + C treatment of this population does not affect helper factor generation. In contrast, alpha p23,30 + C treatment of the allogeneic stimulator cell population eliminates helper factor production. Taken together, these results demonstrate that interaction between Ia-bearing stimulator cells and Ia- responder T cells is required for the production of MLC-derived helper factor. In additional experiments, we determined that alpha p23,30, in the absence of C, totally abrogates the PFC response triggered by MLC helper factors. This result suggests an important role for Ia antigens in the functional activity of preformed helper factor molecules.     

Enhanced TNP-reactive helper T cell activity and its utilization in the induction of amplified tumor immunity that results in tumor regression

The present study was designed to investigate the generation of trinitrophenyl (TNP)-reactive helper T cell activity potent enough to induce the regression of a syngeneic tumor; this occurs by augmenting antitumor-specific immunity through T-T cell interaction. Mice whose skin was painted with trinitrochlorobenzene (TNCB) exhibited a variety of anti-TNP T cell responses, including delayed-type hypersensitivity (DTH) and cytotoxic T cell responses, as well as helper T cell activity. Pretreatment of C3H/He mice with TNP-conjugated copolymer of D-glutamic acid and lysine (TNP-D-GL) or cyclophosphamide, which have been shown, respectively, to inactivate TNP-specific suppressor T cells or suppressor T cells in general, exhibited a slight or marginal augmentation of DTH and cytotoxic potentials when tested 5 wk after TNCB painting. In contrast, the same pretreatment regimens induced an appreciably amplified generation of anti-TNP helper T cell activity. This amplified TNP-helper T cell activity was demonstrated to enhance cytotoxic responses to antigens other than TNP in an antigen-nonspecific way. In fact, such helper T cells enhanced antitumor CTL responses when co-cultured with spleen cells from syngeneic X5563 plasmacytoma-bearing mice in the presence of TNBS-modified X5563 tumor cells. This amplified TNP-helper cell system was utilized for its immunotherapeutic potential. When TNCB was injected into X5563 tumor mass of syngeneic C3H/He mice in which the amplified TNP-helper T cell activity had been generated, an appreciable number of growing tumors was observed to regress. This contrasted with the low incidence of tumor regression observed in mice in which TNP-helper activity had been induced by TNCB painting without inactivation of suppressors. Thus, the present model provides an effective immunotherapeutic manipulation for eliciting enhanced in vivo tumor regression, and emphasizes a role of helper T cells in augmentation of syngeneic tumor immunity.     

Generation of T helper cells in vitro. IV. F1 T helper cells primed with antigen-pulsed parental macrophages are genetically restricted in their antigen-specific helper activity.

A sequential culture technique for the in vitro induction and subsequent assay of T helper cells is employed to examine the histocompatibility requirements for antigen recognition by murine T helper cells. F1 T cells are primed in vitro with antigen-pulsed parental strain macrophages and tested for antigen-specific helper activity in cultures containing anti-Thy 1.2 serum and C treated spleen cells from hapten-primed parental or F1 mice. A semiallogenieic system is used and appropriate controls are included to avoid possible complicating effects of allogeneic interactions. The results indicate that F1 T helper cells preferentially stimulate carrier-specific anti-hapten plaque-forming cell responses in spleen cells which are H-2 identical with the macrophage used initially to prime the T cells. Parental spleen cell cultures do not respond to F1 T helper cells which were primed with the other parental strain macrophage. Supplementing this culture with macrophages which are histocompatible with those used to prime the F1T cells is sufficient to restore T helper cell activity. Thus, the genetic restriction described here is between the primed T cell and the macrophage used to elicit secondary responses and not between the T cell and B cell. The results in this semiallogeneic system, however, do not rule out the possibility of additional allogeneic genetic restrictions in the subsequent interaction of T cells with B cells.     

Activation of B cells by autoreactive T cells: cloned autoreactive T cells activate B cells by two distinct pathways

Although the existence of autoreactive T cells has been widely reported, the functional capacities of these populations have been less well defined. Studies were therefore carried out to characterize the relationship of autoreactive T cells to antigen-specific major histocompatibility complex (MHC)-restricted T cells in their ability to act as helper cells for the induction of immunoglobulin synthesis by B cells. A number of autoreactive T cell lines and clones were isolated from antigen-primed spleen and lymph node cell populations. Autoreactive T cells were found to proliferate in response to direct recognition of syngeneic I-A or I-E subregion-encoded antigens in the absence of any apparent foreign antigen. It was shown that cloned autoreactive T cells were capable of activating B cell responses through two distinct pathways. After appropriate stimulation by syngeneic cells, autoreactive T cells polyclonally activated primed or unprimed B cells to synthesize IgM antibodies. These activated T cells functioned in these responses through an MHC-unrestricted pathway in which polyclonal responses were induced in both syngeneic and allogeneic B cells. These cloned autoreactive T cells were also able to activate IgG responses by primed B cells through a different activation pathway. In contrast to the polyclonal activation of IgM responses, the induction of IgG antibodies by the same cloned T cells required primed B cells and stimulation with the priming antigen. The activation of B cells to produce IgG was strongly MHC restricted and required the direct recognition by the autoreactive T cells of self MHC determinants expressed on the B cell surface, with no bystander activation of allogeneic B cells. These results indicate that cloned autoreactive T cells resemble antigen-specific MHC-restricted T cells in their ability to function as T helper cells through distinct MHC-restricted and MHC-unrestricted pathways.     

The induction in vitro of immunological tolerance in T lymphocytes: an inhibitory role of macrophages.

Hapten-reactive helper T cells were generated in the spleen of C57BL/6 mice primed with sulfanilated syngeneic IgG (S-MGG). Specific immunological tolerance was induced in vitro in these helper T cells, when spleen cell suspension was passed through Sephadex G-10 column to remove adherent cells and cultured in the presence of soluble S-MGG for 21 to 24 hours. On the other hand, tolerance was not inducible in unfractionated, primed spleen cells. When G-10-passed spleen cells were added to the culture dishes containing phagocytic, adherent cells of the spleen, tolerance was no more inducible in these reconstituted cell population. From these experimental results, it was concluded that macrophages played an interfering role in tolerance induction. The experimental data were also discussed in terms of macrophage function in the recognition of antigen by T lymphocytes.     

Pulmonary infection with influenza A virus induces site-specific germinal center and T follicular helper cell responses

Protection from influenza A virus (IAV) challenge requires switched, high affinity Abs derived from long-lived memory B cells and plasma cells. These B cell subsets are generated in germinal centers (GCs), hallmark structures of T helper cell-driven B cell immunity. A full understanding of the GC reaction after respiratory IAV infection is lacking, as is the characterization of T follicular helper (T(FH)) cells that support GCs. Here, GC B cell and T(FH) cell responses were studied in mice following pulmonary challenge with IAV. Marked GC reactions were induced in draining lymph nodes (dLNs), lung, spleen and nasal-associated lymphoid tissue (NALT), although the magnitude and kinetics of the response was site-specific. Examination of switching within GCs demonstrated IgG2(+) cells to compose the largest fraction in dLNs, lung and spleen. IgA(+) GC B cells were infrequent in these sites, but composed a significant subset of the switched GC population in NALT. Further experiments demonstrated splenectomized mice to withstand a lethal recall challenge, suggesting the spleen to be unnecessary for long-term protection in spite of strong GC responses in this organ. Final studies showed that T(FH) cell numbers were highest in dLNs and spleen, and peaked in all sites prior to the height of the GC reaction. T(FH) cells purified from dLNs generated IL-21 and IFNγ upon activation, although CD4(+)CXCR5(-) T effector cells produced higher levels of all cytokines. Collectively, these findings reveal respiratory IAV infection to induce strong T helper cell-driven B cell responses in various organs, with each site displaying unique attributes.     

The murine IL 2 receptor. III. Cellular requirements for the induction of IL 2 receptor expression on T cell subpopulations

The accessory cell requirements for the induction of the IL 2 receptor by the lectin Con A on murine T cell subsets were directly assayed with anti-IL 2 receptor monoclonal antibodies. Substantial levels of IL 2 receptor expression were induced on T lymphocytes of the MHC class I-restricted, suppressor/cytotoxic phenotype (L3T4-, Ly-2+) in the presence and absence of accessory cells. In contrast, high levels of IL 2 receptor expression could only be induced on T cells of the MHC class II-restricted, helper/inducer phenotype (L3T4+, LY-2-) in the presence, but not in the absence, of accessory cells. Ia- cells such as the P388D1 macrophage line or cultured fibroblasts (DAP X 3) were as efficient as the Ia+ B cell hybridoma LB in providing accessory cell function for the L3T4+, Ly-2- subset. PMA, but not purified human IL 1, could substitute for accessory cells for both IL 2 receptor expression and IL 2 secretion by the L3T4+, Ly-2- subset. These data suggest that IL 2 receptor induction on the L3T4+, Ly-2- subset is complex, possibly requiring a T cell-accessory cell interaction, whereas the lectin may directly trigger IL 2 receptor expression on L3T4-, Ly-2+ T cells.     

Major-histocompatibility-complex-class-II-positive cells and interleukin-2-dependent proliferation of immune T cells are required to reject carcinoma cells in the guinea pig

Summary Tumor immunity induced by bacillus Calmette-Guérin was studied in the line 10 hepatocellular carcinoma (line 10) in the strain-2 guinea pig. Line 10 immunity was investigatedin vitro with a lymphocyte proliferation assay using line 10 tumor protein extracted with 3 M KCl andin vivo by adoptive transfer of line-10-immune spleen cells. Monoclonal antibodies against guinea pig leucocyte markers were used to block functional properties of the immune cells in order to determine which cell types or cell markers are involved in the immune response to the line 10 tumor.In vitro cells from the spleen, peripheral blood and regional lymph node of immune animals reacted with a proliferative response to line 10 protein. This antigen-specific response was caused by T cells and was regulated by major histocompatibility complex (MHC) class II molecules. In blocking experiments it was found that CT5 (anti-PanT), or MSgp4 [anti-(MHC class I antigen)] monoclonal antibodies did not block but some-times stimulated the proliferative response. The effect of H159 (anti-PanT) was irregular, while H155 [anti-(T helper)], and 5C3 [anti-(IL-2 receptor)] monoclonal antibodies blocked the response almost completely. We studied the relevance of the resultsin vitro obtained and found that mAb 5C3 [anti-(IL-2 receptor)] inhibited the adoptive transfer of line 10 immunity, suggesting that the rejection of line 10 cells is caused by a mechanism that is interleukin-2 (IL-2)-dependent. Moreover, complement lysis of MHC-class-II-antigen-positive immune spleen cells inhibited completely the rejection of the line 10 tumor cell challenge in the adoptive-transfer experiments. In conclusion, our data show that MHC class II molecules or cells possessing these molecules are involved in immunity against line 10 tumor cells, as (a) monoclonal antibodies against MHC class II antigens inhibited thein vitro proliferative response of T cells to tumor antigens and (b) removal of MHC-class-II-positive immune spleen cells abrogated the antitumor effect in the adoptive-transfer experiments. Interleukin-2-dependent proliferation of immune T cells is required for the rejection of line 10 tumor cells.     

Urtica dioica agglutinin, a new mitogen for murine T lymphocytes: unaltered interleukin-1 production but late interleukin 2-mediated proliferation

Urtica dioica agglutinin, a small-molecular-weight lectin purified from stinging nettle rhizomes, induces murine cell proliferation. U. dioica agglutinin is a specific T-cell mitogen for both thymocytes and spleen T lymphocytes; its mitogenic properties are strictly dependent on the presence of accessory cells. The kinetics of proliferation are markedly different from those of the classical T-cell mitogen concanavalin A, with a 2 to 3-day delay for both splenic and thymic populations and a rate of DNA synthesis twofold lower than that observed with concanavalin A. The late T-lymphocyte proliferation induced by U. dioica agglutinin correlates well with (i) the observed late interleukin-2 production and interleukin-2 receptor expression, and (ii) the long-lasting cyclosporin A-sensitive early activation period. In contrast, the production of interleukin-1 is not different, both in terms of concentration and kinetics, from that observed with concanavalin A.     

T cell-dependent hapten-specific and polyclonal B cell responses require release of interleukin 5

CD4+ T cells in the mouse have recently been subdivided into two major subpopulations which differ in their functional activities and in the lymphokines they produce. Although cloned T cells lines representative of both sets will activate B cells in polyclonal responses, only the subset producing interleukin 4 (IL-4) will activate antigen-specific B cells in linked recognition assays. This suggested that IL-4 was essential for such responses. In the present experiments, the requirements were compared for B cell activation in specific as opposed to polyclonal antibody responses by T cell clones of the helper (IL-4 producing) subset. It was found that specific responses involve primarily small B cells, whereas polyclonal responses activate exclusively the large B cells. Second, polyclonal B cell responses can proceed in the absence of T:B contact, whereas specific responses require physical interaction of the two cells. Third, it was found that interleukin 5 (IL-5, formerly known as T cell replacing factor/B cell growth factor II) is essential for these polyclonal responses by inhibition of such responses with monoclonal anti-IL-5 antibody. Anti-IL-5 also inhibits specific antibody responses involving direct T:B interaction. Thus, IL-5 is clearly a critical mediator of differentiation to immunoglobulin secretion of activated B cells, whether such B cells are obtained as large B cells from freshly isolated spleen cells or are initially activated in an IL-4-dependent fashion by cognate interaction by a helper T cell clone.