Subpopulations of B cells distinguished by cell surface expression of Ia antigens. Correlation of Ia and idiotype during activation by cloned Ia-restricted T cells

We have investigated in vitro the induction of antibody responses to phosphorylcholine (PC) by cloned T helper (Th) cell lines. The cloned Th cells are antigen specific, in this case ovalbumin (OVA), self-Ia recognizing, and induce antibody secretion only if the hapten, PC, is physically linked to the carrier (OVA) molecule. The plaque-forming cell (PFC) response generated in the presence of cloned Th cells is idiotypically diverse with 5-40% of the secreting B cells bearing the TEPC-15 (T15) idiotype. The interaction of the cloned Th cells and unprimed B cells requires recognition of B cell surface Ia glycoproteins for all B cells activated to secrete anti-PC antibody, whether they be T15-bearing or not. More importantly, however, effective interaction between a cloned Th cell and a B cell is determined by the quantity of B cell surface Ia glycoproteins. Our results indicate that quantitative differences in B cell surface Ia antigens are directly related to B cell activation by the cloned Th cell. The high Ia density B cells are most easily activated by cloned Th cells, and these appear to be mainly non-T15-bearing. These data suggest that the failure of cloned Th cells to effectively activate T15-bearing B cells in vitro may be due to the lower relative Ia density of these B cells and therefore to their inability to interact effectively with cloned Ia-recognizing Th cells. These results imply that monoclonal T cells may distinguish between T15-bearing and non-T15-bearing B cells based on their Ia density.     

Antigen-binding T cells as helper cells. Separation of helper cells by immune rosette formation

The spleen T cells from mice immunized 6 days earlier with either chicken gamma globulin (CGG) or with donkey erythrocytes (DRC) were rosetted with CGG-coated sheep erythrocytes or with DRC. The immune rosettes (RFC) (antigen-binding cells) were separated from the bulk of nonrosette-forming cells (non-RFC) by 1-g velocity sedimentation and the RFC and non-RFC tested for helper activity in cooperative antihapten responses in vitro. RFC or non-RFC were mixed with normal or hapten-primed spleen cells, challenged with the appropriate hapten-carrier conjugate and cultured for 4 days in Marbrook tissue cultures. The helping activity was quantitated from the numbers of antihapten antibody-producing cells generated per culture. The results show that specific helper cell activity could be selectively recovered in the immune rosette-forming cell population whereas the non-RFC population was depleted of help. These findings indicate that the helper T cells express specific antigen binding receptors.     

Distinct functional lineages of human V(alpha)24 natural killer T cells

CD1d-restricted autoreactive natural killer (NK)T cells have been reported to regulate a range of disease conditions, including type I diabetes and immune rejection of cancer, through the secretion of either T helper (Th)2 or Th1 cytokines. However, mechanisms underlying Th2 versus Th1 cytokine secretion by these cells are not well understood. Since most healthy subjects express <1 NKT cell per 1,000 peripheral blood lymphocytes (PBLs), we devised a new method based on the combined used of T cell receptor (TCR)-specific reagents alpha-galactosylceramide (alphaGalCer) loaded CD1d-tetramers and anti-V(alpha)24 monoclonal antibody, to specifically identify and characterize these rare cells in fresh PBLs. We report here that CD4(+) and CD4(-)CD8(-) (double negative [DN]) NKT cell subsets represent functionally distinct lineages with marked differences in their profile of cytokine secretion and pattern of expression of chemokine receptors, integrins, and NK receptors. CD4(+) NKT cells were the exclusive producers of interleukin (IL)-4 and IL-13 upon primary stimulation, whereas DN NKT cells had a strict Th1 profile and prominently expressed several NK lineage receptors. These findings may explain how NKT cells could promote Th2 responses in some conditions and Th1 in others, and should be taken into consideration for intervention in relevant diseases.     

Requirement for three signals in B cell responses. II. Analysis of antigen- and Ia-restricted T helper cell-B cell interaction

We have recently reported that resting B cells must receive at least three different signals in a T helper cell (TH)-dependent as well as in a lipopolysaccharide (LPS)-induced B cell response (3), i.e., a specific TH signal (that can be bypassed by LPS), a nonspecific TH signal (mediated by Ia or antigen-nonspecific B cell helper factor), and an antigen (hapten) signal. In a system using male (H-Y) antigen- specific cloned TH of C57BL/6 origin and male (or female) B cells, we now confirm and extend these findings by demonstrating that H-Y- specific TH must see both H-Y and Ia determinants on the B cells (and not only on macrophages) to provide the first specific TH signal required for a plaque-forming cell (PFC) response. This signal was interfered with by a monoclonal anti-I-Ab antibody at the B cell level, was not mediated by detectable soluble factors (in contrast to the nonspecific signal also provided by the TH), and could be bypassed by LPS, in which case anti-I-Ab antibody had no effect. However, although the H-Y-specific TH induced a polyclonal PFC response (B cell differentiation) in the apparent absence of an antigen seen by the B cells, significant clonal expansion of PFC precursors occurred only when the B cells also recognized an antigen (hapten).     

Lymphokine-mediated regulation of the proliferative response of clones of T helper 1 and T helper 2 cells

Murine Th1 and Th2 subsets differ not only in the lymphokines they produce, but also functionally. It is not clear what factors influence the preferential activation of one subset versus the other and what regulatory interactions exist between them. The purpose of this study was to examine the effect of lymphokines produced by clones of Th1 cells (IL-2 and IFN-gamma), Th2 cells (IL-4), and APC (IL-1) on the proliferative response of Th1 and Th2 cells after antigenic stimulation. Activation of both types of clones in the presence of antigen and APC resulted in the acquisition of responsiveness to the proliferative effects of both IL-2 and IL-4, although Th2 cells were more responsive to IL-4 than Th1 cells. Responsiveness of Th1 and Th2 cells to both lymphokines decreased with time after initial antigenic activation; Th1 cells lost their responsiveness to IL-4 more rapidly and to IL-2 more slowly than Th2 cells. IFN-gamma partially inhibited the IL-2 and IL-4-mediated proliferation of Th2, but not Th1 cells. Although the presence of IL-1 was not required for the response of Th1 or Th2 cells to IL-4, its presence resulted in a synergistic effect with IL-2 or IL-4 in Th2 but not in Th1 cells. Both subsets responded to a mixture of IL-2 and IL-4 in synergistic fashion. Delayed addition and wash-out experiments indicated that both IL-2 and IL-4 had to be present simultaneously in order for synergy to occur. These results suggest that Th cell subsets might regulate each other via the lymphokines that they secrete and that the pathways of IL-2 and IL-4 mediated proliferation are interrelated.     

T helper 1 and T helper 2 cells are pathogenic in an antigen-specific model of colitis.

Dysregulated T cell responses to enteric bacteria have been implicated as a common mechanism underlying pathogenesis in rodent models of colitis. However, the bacterial species and T cell specificities that induce disease have been poorly defined. We have developed a model system in which target antigen, bacterial host, and corresponding T cell specificity are defined. OVA-specific T cells from DO11.RAG-2(-/-) TCR transgenic mice were transferred into RAG-2(-/-) recipients whose intestinal tracts were colonized with OVA-expressing or control Escherichia coli. Transfer of antigen-naive DO11.RAG-2(-/-) T cells into recipients colonized with OVA-E. coli resulted in enhanced intestinal recruitment and cell cycling of OVA-specific T cells; however, there was no development of disease. In contrast, transfer of polarized T helper (Th) 1 and Th2 populations resulted in severe wasting and colitis in recipients colonized with OVA-expressing but not control E. coli. The histopathologic features of disease induced by Th1 and Th2 transfers were distinct, but disease severity was comparable. Induction of disease by both Th1 and Th2 transfers was dependent on bacterially associated OVA. These results establish that a single bacterially associated antigen can drive the progression of colitis mediated by both Th1 and Th2 cells and provide a new model for understanding the immunoregulatory interactions between T cells responsive to gut floral antigens.     

Separation of helper and suppressor T lymphocytes. II. Ly phenotypes and lack of DNA synthesis requirement for the generation of concanavalin A helper and suppressor cells

Using a Ficoll velocity sedimentation gradient, we have been able to fractionate concanavalin A (Con A)-induced helper and suppressor cells into separate pools. Cells activated by Con A to mediate helper activity are Ly1+, do not require DNA synthesis for induction, and remain as small cells after activation. Suppressor cells are Ly23+, are found in the blast cell fraction and their induction is not inhibitable by prior treatment with mitomycin C or irradiation, both of which inhibit DNA synthesis. The implications of such findings are discussed.     

Distinct regulatory roles of lymphocyte costimulatory pathways on T helper type-2 mediated autoimmune disease

We assessed the role of CD40-CD40L, cytotoxic T lymphocyte (CTL)A4/CD28- B7s, and CD2-CD48/CD58 lymphocyte costimulatory pathways in the development of mercury chloride (HgCl2)-induced autoimmune disease in mice, which is believed to be mediated by T helper (Th) subset Th2. Inhibition of CD40-CD40-L and CTLA4/CD28-B7s interactions by anti-CD40- L antibody and soluble CTLA4-immunoglobulin (Ig) fusion protein, respectively, abrogated the autoimmune disease without affecting interleukin 4 (IL-4) production, showing the importance of physical contact between T and B lymphocytes in the Th2-mediated process. In contrast, two anti-CD2 antibodies that have been shown to induce immunosuppression of Th1-mediated events exacerbated the autoantibody response and augmented IgG1, IgE, and IL-4 production, transforming a mild mesangial glomerulopathy into a severe systemic immune complex disease. These observations demonstrate that manipulation of lymphocyte accessory counterreceptor interactions may affect the course of Th2- associated autoimmune disease and suggest that signals resulting from CD2 engagement play an essential role in the regulation of the Th1-Th2 effector equilibrium.     

Cloned mouse cells with natural killer function and cloned suppressor T cells express ultrastructural and biochemical features not shared by cloned inducer T cells

We have examined the morphology, cytochemistry, and biochemistry of mouse leukocyte subsets by analyzing cloned leukocyte populations specialized to perform different immunologic functions. Cloned cells expressing high-affinity plasma membrane receptors for IgE and mediating natural killer (NK) lysis and cloned antigen-specific suppressor T cells contained prominent osmiophilic cytoplasmic granules similar by ultrastructure to those of mouse basophils. Both clones also incorporated 35SO4 into granule-associated sulfated glycosaminoglycans, expressed a characteristic ultrastructural pattern of nonspecific esterase activity, incorporated exogenous [3H]5-hydroxytryptamine, and contained cytoplasmic deposits of particulate glycogen. By contrast, cloned inducer T cells lacked cytoplasmic granules and glycogen, incorporated neither 35SO4 nor [3H]5-hydroxytryptamine, and differed from the other clones in pattern of nonspecific esterase activity. These findings establish that certain cloned cells with NK activity and cloned suppressor T cells express morphologic and biochemical characteristics heretofore associated with basophilic granulocytes. However, these clones differ in surface glycoprotein expression and immunologic function, and the full extent of the similarities and differences among these populations and basophils remains to be determined.     

Both a monoclonal antibody and antisera specific for determinants unique to individual cloned helper T cell lines can substitute for antigen and antigen-presenting cells in the activation of T cells

Two antisera and a monoclonal antibody raised in BALB.K mice against cloned, major histocompatibility complex (MHC)-restricted, antigen-specific helper T cell lines are described. These antibodies are specific for individual cloned T cell lines and are potent inducers of T cell proliferation. The induction of T cell proliferation by these antibodies requires the presence of an adherent accessory cell. There is no H-2 restriction between this accessory cell and the cloned T cell, nor is this antibody-induced proliferation blocked by a monoclonal anti-Fc receptor antibody. The requirement for an accessory cell, however, is eliminated in the presence of an IL-1- or IL-2-rich supernatant. Thus this system allows the analysis of helper T cell activation with only a single cell type present. Anti-T cell sera also induce T cell-dependent B cell proliferation and immunoglobulin secretion. The induction of T cell-dependent B cell activation by these sera does not require H-2-matched T cells and B cells. The specificity of these antibodies and their ability to stimulate cloned helper T cells in the absence of antigen and antigen-presenting cells strongly suggest that these antibodies are directed against antigen and/or Ia recognition sites on the T cell.     

Idiotype-recognizing T helper cells that are not idiotype specific

In this study T helper cells that recognize idiotypes as carriers for a hapten-specific B cell response were analyzed under limiting dilution conditions. T helper cells, induced by phosphorylcholine-hemocyanin (PC-Hy) priming, recognize trinitrophenylated TEPC-15 and MOPC-167 (TNP-T15, TNP-167) equally well. Limiting dilution analysis indicates identical frequencies of helper cells for TNP-T15 and TNP-167. Double immunization protocols using TNP-T15 and TNP-167 fail to demonstrate additive effects. Inhibition of carrier recognition in vitro using free hapten, PC, and unconjugated T15 or M167 indicates identical specificities of helper cells for T15 and M167. Collectively, these results provide strong evidence that PC-Hy priming induces only one population of idiotype-recognizing helper cells that are unable to distinguish between the T15 and the M167 idiotopes. The helper cell induction circuit was further analyzed. PC-Hy priming induces T15/167-specific helper T cells in X-linked immune defect-expressing F1 mice. This indicates that a B cell response to PC is not required to induce idiotype-recognizing T cells. Adoptive cotransfer of B cells from PC-Hy-primed mice together with normal T cells fails to induce idiotype-recognizing T cells. These results indicate the existence of a T helper1-T helper2 induction loop. In this scheme, the T helper1 cell carries T15-like receptors and the T helper2 cells, anti-T15-like receptors. Monoclonal antiidiotypic antibodies specific for T15 also induce a T15/167-recognizing T helper cell population. This finding demonstrates that idiotope-specific priming induces non-idiotype-specific T cells. Evidently, the idiotypic T cell network is based on a different selection of idiotope determinants than the selection of the B cell idiotype network.     

Distinct role of antigen-specific T helper type 1 (Th1) and Th2 cells in tumor eradication in vivo.

The role of T helper type 1 (Th1) and Th2 cells in tumor immunity was investigated using Th cells induced from ovalbumin (OVA)-specific T cell receptor transgenic mice. Although Th1 cells exhibited stronger cytotoxicity than Th2 cells, both cell types completely eradicated tumors when transferred into mice bearing A20 tumor cells transfected with the OVA gene (A20-OVA). Th1 cells eradicated the tumor mass by inducing cellular immunity, whereas Th2 cells destroyed the tumor by inducing tumor necrosis. Both Th1 and Th2 cells required CD8(+) T cells to eliminate tumors, and neither of these cells were able to completely eliminate A20-OVA tumors from T and B cell-deficient RAG2(-/-) mice. Mice cured from tumors by Th1 and Th2 cell therapy rejected A20-OVA upon rechallenge, but CD8(+) cytotoxic T lymphocytes were induced only from spleen cells prepared from cured mice by Th1 cell therapy. Moreover, we demonstrated that Th1 and Th2 cells used distinct adhesion mechanisms during tumor eradication: the leukocyte function-associated antigen (LFA)-1-dependent cell-cell adhesion step was essential for Th1 cell therapy, but not for Th2 cell therapy. These findings demonstrated for the first time the distinct role of antigen-specific Th1 and Th2 cells during eradication of established tumors in vivo.     

滤泡辅助性T细胞在类风湿关节炎发病中的临床意义

目的通过检测类风湿关节炎(RA)患者外周血滤泡辅助性T淋巴细胞(Tfh))和白细胞介素-21(IL-21)等的表达,探讨其在RA发病过程中可能的免疫学发病机制。方法根据病情活动度不同将病例组分为轻、中、重度活动组(各30例),健康对照组30例;流式细胞仪检测RA和健康对照组外周血单个核细胞(PBMCs)中CD4-异硫氰酸荧光素(FITC)、CXCR5-藻红蛋白(PE)、ICOS-别藻蓝蛋白(APC)标记的CD3+CD4+CXCR+、CD3+CD4+ICOS+及CD3+CD4+CXCR+ICOS+Tfh百分率;酶联免疫吸附试验(ELISA)检测IL-21、类风湿因子(RF-IgM)、抗环瓜氨酸肽(CCP)抗体(CCP-IgG)及红细胞沉降率(ESR)、C反应蛋白(CRP),分析其与Tfh的相关性。结果 RA轻、中、重度活动组患者外周血中Tfh百分率明显高于健康对照组(P0.05);Tfh百分率随着RA活动度的增加呈上升趋势,组间差异有统计学意义(P0.05);Tfh细胞百分率与RA患者ESR、CRP、RF及抗CCP抗体滴度呈正相关,差异有统计学意义(P0.05)。结论 RA患者外周血Tfh、IL-21、CRP、ESR、RF及CCP水平明显升高,与疾病活动度等有明显相关性,提示Tfh细胞可能在RA发病中起着一定的作用。     

Clonal analysis of F1 hybrid helper T cells. I-A subregion-encoded hybrid determinants restrict the activity of keyhole limpet hemocyanin- specific helper T cells

Clonal expansion of isolated precursors to helper T cells was induced in limiting dilution cultures of keyhole limpet hemocyanin (KLH)-primed F1 hybrid lymph node cells. Progeny of each isolated precursor was tested for helper activity by transfer to independent cultures with hapten-primed B cells of either parental or F1 hybrid origin. The major histocompatibility complex (MHC) restriction specificity of each F1 hybrid helper T clone was determined. To assess the contribution of I-A and I-E subregion-encoded genes to the expression of these restriction elements, helper T cell cultures derived from F1 hybrids between strains with recombinant H-2 haplotypes were analyzed. Parental and unique F1 hybrid MHC determinants that are encoded entirely within the I-A subregion were found to restrict the activity of KLH-specific helper T cells.     

T cell receptor-independent immunosuppression induced by dexamethasone in murine T helper cells.

The immune and inflammatory responses are largely inhibited by glucocorticosteroids. In thymocytes, for example, glucocorticosteroids cause apoptosis, whereas they suppress the activity of phospholipase A2 and the production of eicosanoids in tissues actively engaged in inflammation. The immunosuppressive action of dexamethasone (DEX) was studied in vitro by employing a model cell system, namely the murine Th2 clone D10.G4.1 (D10) and its clonotypic anti-T cell receptor (TCR) mAb 3D3. Although the proliferative response of D10 cells to 3D3 stimulation was not affected by DEX, the costimulation provided by IL-1 was dramatically inhibited. Substitution of 3D3 by exogenous IL-4 (as the IL-1 costimulant) failed to prevent the inhibition of proliferation caused by DEX. Yet, when 3D3-mediated stimulation of TCR was supplemented with IL-2, D10 cells were capable of proliferating, even in the presence of DEX. Thus, TCR stimulation on D10 cells remained intact and their resulting propagation was not compromised by DEX treatment. These results provide evidence that immunosuppression caused by DEX is TCR independent and involves an early cytokine-signalling event.     

Viral persistence redirects CD4 T cell differentiation toward T follicular helper cells

CD4 T cell responses are crucial to prevent and control viral infection; however, virus-specific CD4 T cell activity is considered to be rapidly lost during many persistent viral infections. This is largely caused by the fact that during viral persistence CD4 T cells do not produce the classical Th1 cytokines associated with control of acute viral infections. Considering that CD4 T cell help is critical for both CD8 T cell and B cell functions, it is unclear how CD4 T cells can lose responsiveness but continue to sustain long-term control of persistent viral replication. We now demonstrate that CD4 T cell function is not extinguished as a result of viral persistence. Instead, viral persistence and prolonged T cell receptor stimulation progressively redirects CD4 T cell development away from the Th1 response induced during an acute infection toward T follicular helper cells. Importantly, this sustained CD4 T cell functionality is critical to maintain immunity and ultimately aid in the control of persistent viral infection.     

HIV and T follicular helper cells: a dangerous relationship

HIV infection leads to progressive destruction of infected CD4 T cells, hypergammaglobulinemia, and loss of memory B cells. Germinal centers, which are key to memory B cell formation and protective antibody responses, are major HIV reservoirs in which the virus replicates within T follicular helper (TFH) cells. In this issue of the JCI, the Koup and Streeck groups report that chronic SIV/HIV infection promotes TFH cell accumulation, which may drive B cell dysregulation. Their discoveries suggest that HIV harnesses TFH cells to evade the antibody response.