Involvement of Lyt-2 and L3T4 in activation of hapten-specific Lyt-2+ L3T4+ T-cell clones

The murine T-cell surface molecules Lyt-2 and L3T4 play a role in the activation of antigen-specific T cells. The currently accepted model for the function of these molecules proposes that Lyt-2 and L3T4 increase the overall avidity of the interaction between the T-cell antigen receptor and antigen in association with the major histocompatibility complex (MHC) molecules on the antigen-presenting cell. We have used two unusual Lyt-2+ L3T4+ class II MHC-restricted T-cell clones to test whether Lyt-2 can substitute for L3T4 when the T-cell antigen receptor is class II MHC-restricted. Monoclonal antibodies against L3T4 profoundly inhibited antigen-induced lymphokine production by both T-cell clones. Anti-Lyt-2 monoclonal antibody had no effect. These results strongly suggest that L3T4 and the class II-restricted T-cell antigen receptors are physically close during antigen recognition, probably as part of a multimolecular complex from which Lyt-2 is excluded. The ability of L3T4 but not Lyt-2 to participate in such a complex with class II-restricted T-cell antigen receptors may explain the striking correlation between class II restriction and L3T4 expression in the peripheral T-cell pool.     

Magnitude of response of histocompatibility-restricted T-cell clones is a function of the product of the concentrations of antigen and Ia molecules.

The activation of specific T-cell clones by antigens is dependent upon the corecognition of restriction elements expressed on antigen-presenting cells (APC). For clones that respond by proliferation and lymphokine production, the restriction element is usually an Ia (I-region-associated) molecule. We show here that the magnitude of the proliferative response of such clones is a function of the product of antigen concentration and the number of Ia molecules expressed on APC. This conclusion was reached through the study of antigen concentration-response curves of T-cell clones specific for pigeon cytochrome c. These curves are characterized by a peak in thymidine incorporation, followed by a decrease in the magnitude of the response as antigen concentrations are increased. The decline in response at high concentrations was not the consequence of the emergence of suppressor cells in the APC population, as it was observed when cells of a cloned B-cell hybridoma line were used to present pigeon cytochrome c to these T-cell clones. The critical role of both antigen concentration and the number of Ia molecules on the APC in determining the magnitude of proliferation was demonstrated in several ways. (i) An inverse relationship was observed between the antigen concentration required for maximum proliferation and the number of APC present in culture. At high antigen concentrations, which caused responses less than maximum, reducing the number of APC actually increased the magnitude of the antigen-induced proliferation. (ii) Decreasing the number of relevant Ia molecules per APC (i.e., as in F1 hybrids) resulted in the requirement for an increased antigen concentration for maximal response and in enhanced proliferation at high antigen concentrations. (iii) In the presence of anti-Ia antibody, higher concentrations of antigen were required for maximal response; at high antigen concentrations, proliferation was enhanced in the presence of a monoclonal anti-Ia antibody directed against the Ia restriction element.     

Salmonella-reactive synovial fluid T-cell clones in a patient with post-infectious Salmonella arthritis

From a patient with reactive arthritis following Salmonella typhimurium enteritis, synovial fluid T-lymphocytes were cloned and expanded in vitro. Seven out of 74 clones showed a marked proliferative response to antigens of heat-killed Salmonella typhimurium with autologous T-cell-depleted peripheral blood mononuclear cells as antigen-presenting cells. The Salmonella-reactive clones were of the CD4+ phenotype, antigen-induced proliferation could be inhibited by a monoclonal antibody to HLA class II. One clone recognized both Salmonella and Campylobacter jejuni antigens in the proliferation assay. The multiclonality of Salmonella-reactive synovial fluid T-cells indicates that the microorganisms have been present, at least transiently, within the affected joint and thus recruited specific T-lymphocytes that might initiate synovitis.     

Triggering of the T3-Ti antigen-receptor complex results in clonal T-cell proliferation through an interleukin 2-dependent autocrine pathway.

Human T-cell clones and anti-T-cell-receptor antibodies (clonotypic) directed at surface receptors for antigen (T3-Ti molecular complex) as well as anti-interleukin 2 (IL-2) and anti-IL-2-receptor antibodies were utilized to investigate the mechanism by which alloantigens or antigen plus self-major histocompatibility complex (MHC) (i.e., physiologic ligand) trigger specific clonal proliferation. Soluble or Sepharose-bound anti-Ti monoclonal antibodies, like physiologic ligand, enhanced proliferative responses to purified IL-2 by inducing a 6-fold increase in surface IL-2 receptor expression. In contrast, only Sepharose-bound anti-Ti or physiologic ligand triggered endogenous clonal IL-2 production and resulted in subsequent proliferation. The latter was blocked by antibodies directed at either the IL-2 receptor or IL-2 itself. These results suggest that induction of IL-2 receptor expression but not IL-2 release occurs in the absence of T3-Ti receptor cross-linking. Perhaps more importantly, the findings demonstrate that antigen-induced proliferation is mediated through an autocrine pathway involving endogenous IL-2 production, release, and subsequent binding to IL-2 receptors.     

Separation of antibody helper and antibody suppressor human T cells by using soybean agglutinin.

Soybean agglutinin (SBA) binds specifically to mouse B cells and has been used in the past to separate mouse B and T spleen cells by differential agglutination of the B cells. In the present study it was found that a major T-cell subpopulation of human peripheral blood mononuclear cells is agglutinated by SBA along with the B cells and monocytes. Tests of such cell surface markers as Fc receptors for IgG and IgM, as well as functional assays of antibody production by B cells, revealed that the SBA-agglutinated cell fraction contains the antibody helper T cells whereas the unagglutinated fraction is enriched with antibody suppressor T cells. Similar observations were made in tests of the proliferative response to mumps antigen. A recently prepared monoclonal antibody, anti-Leu 2a, which recognized the same thymus-dependent antigen previously defined by a heterologous anti-human T cell serum (alpha TH2), was found to define by indirect immunofluorescence a subpopulation of SBA- cells of intermediate staining intensity which was not detectable in the SBA+ population.     

Inhibition of functional properties of tetanus antigen-specific T-cell clones by envelope glycoprotein GP120 of human immunodeficiency virus

We investigated mechanisms by which the soluble native envelope glycoprotein gp120 of the human immunodeficiency virus (HIV-1) suppresses antigen-driven T cell responses. For this study, exogenous interleukin-2 (IL-2)-independent, antigen-specific, CD4 positive, human T-cell clones were developed by cyclic restimulation with soluble tetanus toxoid antigen. In the presence of soluble antigen and antigen-presenting cells (APC), T-cell clones proliferated and secreted IL-2. Purified gp120 suppressed the proliferative responses of the T-cell clones with concomitant suppression of IL-2 secretion; proliferative responses of CD8+ T cells preincubated with gp120 were not inhibited. A short pulse of 20 minutes with gp120 was sufficient to inhibit the proliferative response of the T-cell clones. Anti-CD3 monoclonal antibody (MoAb)-driven proliferation of the T-cell clones was also suppressed by gp120, but responses elicited by mitogens, phorbol myristate acetate (PMA) plus calcium ionophore, ionomycin, anti-CD2 MoAbs, and a combination of anti-CD3 plus anti-CD28 MoAb driven responses remained unaffected. Investigation of signal transduction events showed that antigen-driven early activation signals via translocation of protein kinase C (PKC), increase in intracellular inositol phosphates, and increase in intracellular calcium were suppressed in gp120 pretreated, tetanus toxoid antigen-stimulated T-cell clones. One mechanism of immune suppression by gp120 may involve interference with the initiation of signal transduction through the T-cell receptor complex.     

Hybrid hybridoma producing a bispecific monoclonal antibody that can focus effector T-cell activity

Previous studies have shown that heteroconjugates of monoclonal antibodies in which one of the component antibodies is directed at the T-cell receptor and the other is directed against any chosen site can focus effector T cells to function at the targeted site. We report here the production of a hybrid hybridoma cell line, H1.10.1.6, which secretes large amounts of a bispecific hybrid antibody of the IgG2a class, that can focus T-cell activity. The parental hybridoma lines for the secondary fusion were F23.1, which secretes an antibody specific for an allotypic determinant on the T-cell receptor of most mouse strains, and 19E12, secreting an anti-Thy-1.1 antibody. The bispecific hybrid antibody was partially purified by hydroxylapatite chromatography and characterized by isoelectric focusing. It efficiently targets Thy-1.1-expressing tumor cells for lysis by F23.1 receptor-positive cytotoxic T-cell clones in vitro. Such hybrid antibodies produced by hybrid hybridoma cell lines may have application in the therapeutic targeting of tumors or sites of viral infections for attack by T cells.     

B-cell stimulatory factor 1 and not interleukin 2 is the autocrine growth factor for some helper T lymphocytes

Clonal expansion of T lymphocytes of the helper/inducer class is generally thought to be mediated by an interleukin 2 (IL-2)-dependent autocrine mechanism. Thus, T cells stimulated by antigens or mitogenic lectins secrete IL-2 and, under appropriate conditions, express membrane receptors for IL-2, and the specific hormone-receptor interaction induces cellular proliferation. Recent studies indicate that B-cell stimulatory factor 1 (BSF-1) is secreted by T cells and is capable of stimulating T-cell proliferation. We now report that BSF-1 and not IL-2 is the sole autocrine growth factor for certain cloned lines of inducer T lymphocytes. On stimulation by the lectin concanavalin A, anti-receptor antibody, or specific antigen with antigen-presenting cells, such clones secrete a lymphokine that stimulates DNA synthesis by the "IL-2 indicator line," HT2, but is identified as BSF-1 by specific inhibition with monoclonal antibodies. The proliferative response of such BSF-1-secreting clones to receptor-mediated signals is dependent on BSF-1 and not IL-2. These results demonstrate a function of BSF-1 and confirm the existence of a previously unknown autocrine pathway of T-cell activation.     

Platelet activation by CD9 monoclonal antibodies is mediated by the FCγII receptor

The function of the human cell surface CD9 antigen is not known, yet monoclonal antibodies (mAbs) of the IgG1 subclass in the CD9 cluster induce activation of platelets. Previously it had been shown that this activation pathway is comparable both in kinetics and extent to physiological agonists such as thrombin. Here it is demonstrated that activation with CD9 mAbs depends on interaction of the Fc part of the CD9 antibody molecule with Fc receptors on the platelet surface, since: (i) mAb directed against the Fc receptor totally blocked the platelet response to CD9 mAb; and (ii) F(ab')2 fragments of the CD9 mAb SYB-1 which bound to platelets, as demonstrated by flow cytometry, failed to activate them. Furthermore, platelet activation by CD9 mAb closely paralleled the activation caused by cross-linking Fc receptors when comparing: (i) kinetics and extent of aggregation; (ii) thromboxane synthesis; (iii) calcium flux; and (iv) the cytoplasmic alkalinization response. Thus it is concluded that CD9 antigen itself does not necessarily participate in stimulus-response coupling leading to platelet activation by CD9 mAbs, and that this activation can be entirely accounted for by the Fc receptor pathway mechanism. The results suggest a possible novel mechanism for platelet consumption in cases of immune thrombocytopenia.     

Coaggregation of the T-cell receptor with CD4 and other T-cell surface molecules enhances T-cell activation

The CD4 molecule, expressed by T cells restricted by class II major histocompatibility complex (MHC) molecules, is believed to play a role in T-cell activation. We have previously suggested that CD4 interacts with the T-cell receptor for antigen (TCR) and with class II MHC and that this dual interaction stabilizes the bond between the TCR and antigen in association with MHC. To investigate the contribution of CD4-TCR interaction, we have used the murine monoclonal anti-TCR V beta 8 antibody F23.1 to activate cloned T cells. Weak activation by soluble biotinylated F23.1 was markedly enhanced by crosslinking with either avidin or with anti-immunoglobulin (anti-Ig). The monoclonal anti-L3T4 antibody GK1.5, which normally inhibits the activation induced by F23.1, did not inhibit when GK1.5 and F23.1 were coaggregated on T cells by anti-Ig, and in many experiments activation was enhanced. Coaggregation of anti-Thy-1.2, anti-H-2Kk, or anti-LFA-1 with F23.1 also enhanced T-cell activation, although, unlike GK1.5, these antibodies in soluble form had no effect on the response to F23.1. These results are consistent with a model for T-cell activation that proposes a primary interaction between L3T4 and the TCR to stabilize TCR complexes and so to enhance T-cell activation. A related but less specific accessory role for other T-cell surface molecules is also suggested. We propose that the cellular interaction that leads to physiological T-cell activation not only achieves TCR ligation but also promotes through their ligation or redistribution the interaction of other T-cell surface molecules, all of which contribute to the overall strength of the activation signal.     

Modulation of the immunological response to hepatitis B virus by antibodies

Antibodies to HBsAg of IgG class enhanced the helper activity of a human T cell clone to promote the in vitro synthesis of immunoglobulins by autologous B lymphocytes. Using two different assay systems, the effect of antigen-specific antibodies on the helper function of a HBsAg-reactive T cell clone was studied. The monoclonal antibody to HBsAg A5C3 (IgG) increased significantly the T cell-dependent production of immunoglobulins by Staphyloccocus aureus-stimulated autologous B lymphocytes. Furthermore, the results obtained with a different type of assay showed that A5C3 also increased the synthesis of antibody to HBsAg by the autologous B cells in the presence of HBsAg and the helper T cell clone. On the other hand, when the monoclonal antibody to HBsAg of IgM class, H5D3 or the F(ab')2 fragment of A5C3 were tested, no significant enhancement of the helper activity of the T cell clone was observed. Experiments performed in mice showed that the in vivo antibody to HBsAg response to low concentrations of HBsAg was significantly enhanced by mixing this antigen with monoclonal antibody to HBsAg of IgG class. No effect was observed when a monoclonal antibody to HBsAg of IgM class was used to prepare the immune-complexed immunogen. The results presented here suggest that antibodies play a critical role in their own production through regulating the activity of helper T cells. This phenomenon might contribute to the increased antibody synthesis of in vivo secondary immune responses and could be of use in designing more efficient vaccine programs in man.     

A peptidoglycan protein complex purified from M. leprae cell walls contains most or all immunodominant M. leprae T-cell antigens

The outcome of an infection with Mycobacterium leprae is correlated with the T-cell-mediated immune response developed against this pathogenic agent. The identification of M. leprae antigens that are recognized by T cells is therefore of great importance. In this paper we present the results of in vitro lymphoproliferation assays in which T-cell reactivity was measured against a peptidoglycan-protein complex (PPC) which was purified from the cell wall of M. leprae. Twelve M. leprae-reactive T-cell clones with different antigen specificities from a tuberculoid (TT) leprosy patient showed proliferative responses, but only when PPC was presented by HLA-DR-matched antigen-presenting cells (APCs). Four of these clones were known to react with the recombinant mycobacterial 65-kDa protein. A tetanus-toxoid-reactive T-cell line from a healthy control was not stimulated by this complex, supporting the idea that the stimulation by PPC was antigen specific. Both PPD-reactive and M. leprae-reactive T-cell lines from healthy individuals were stimulated by PPC. However, when this complex was presented to PPD-reactive T-cell lines derived from two lepromatous (LL) leprosy patients, we did not observe any proliferative responses. From these results we conclude that PPC contains most or all of the antigens which stimulate M. leprae-reactive T cells in association with relevant HLA class II molecules, including the 65-kDa protein or at least some immunogenic parts of it.     

Efficient IgG-mediated suppression of primary antibody responses in Fcgamma receptor-deficient mice

IgG antibodies can suppress more than 99% of the antibody response against the antigen to which they bind. This is used clinically to prevent rhesus-negative (Rh-) women from becoming immunized against Rh+ erythrocytes from their fetuses. The suppressive mechanism is poorly understood, but it has been proposed that IgG/erythrocyte complexes bind to the inhibitory Fc receptor for IgG (FcgammaRIIB) on the B cell surface, thereby triggering negative signals that turn off the B cell. We show that IgG induces the same degree of suppression of the response to sheep erythrocytes in animals lacking the known IgG-binding receptors FcgammaRIIB, FcgammaRI + III, FcgammaRI + IIB + III, and FcRn (the neonatal Fc receptor) as in wild-type animals. Reinvestigation of the ability of F(ab')2 fragments to suppress antibody responses demonstrated that they were nearly as efficient as intact IgG. In addition, monoclonal IgE also was shown to be suppressive. These findings suggest that IgG inhibits antibody responses through Fc-independent mechanisms, most likely by masking of antigenic epitopes, thereby preventing B cells from binding and responding to antigen. In agreement with this, we show that T cell priming is not abolished by passively administered IgG. The results have implications for the understanding of in vivo regulation of antibody responses and Rh prophylaxis.     

Adduction of soluble proteins with malondialdehyde-acetaldehyde (MAA) induces antibody production and enhances T-cell proliferation

BACKGROUND: The alcohol metabolites malondialdehyde and acetaldehyde can combine to form stable adducts (MAA) which are found in the livers of humans and rats after significant alcohol ingestion. While adducted proteins induce antibody responses in the absence of adjuvants, the mechanisms by which these responses occur are unknown. Thus, it was the purpose of these studies to investigate how MAA modification stimulates antibody and T-cell responses in the absence of adjuvants. METHODS: Hen egg lysozyme (HEL) was modified with increasing levels of MAA and was used as an immunogen, and antibody and T-cell responses were determined. The role of scavenger receptors in the immunogenicity of MAA-adducted proteins was also investigated. RESULTS: Maximum antibody response was induced after immunization with 1.8 nM MAA/nM HEL, and was primarily an IgG1 response to HEL as determined by inhibition ELISAs. T-cell proliferative responses after immunization with HEL-MAA were solely to HEL. Immunization with a scavenger receptor ligand in conjunction with HEL-MAA increased the predominant IgG1 response and sharply decreased the IgG2a response by approximately 50%. Binding of HEL-MAA by splenocytes was determined by flow cytometry to be approximately 15% greater than HEL alone, showing a doubling of the geometric mean fluorescence. Also, most of the cells that bound HEL-MAA were class II positive, indicating that antigen-presenting cells can bind the MAA-adducted HEL, and potentially initiate immune responses. CONCLUSIONS: MAA modification of proteins induces antibody and T-cell proliferative responses in vivo. Initial studies suggest that these responses may be mediated by scavenger receptors that recognize MAA-adducted proteins. This suggests a mechanism by which proteins modified with oxidative products associated with chronic ethanol consumption may alter immune responses that may play an active role in the development and/or progression of alcoholic liver disease.     

Superantigen staphylococcal enterotoxin B-induced T-helper cell activation is independent of CD4 molecules and phosphatidylinositol hydrolysis.

The role of the CD4 molecule in activation of T-helper cells was examined by investigating the effect of an anti-CD4 monoclonal antibody (Leu3a) in conventional peptide antigen-specific cloned T-helper cells that are also reactive to staphylococcal enterotoxin B (SEB). These T-helper cell clones are CD4+/CD45RO+/T-cell antigen receptor beta-chain variable region 12-positive and can respond to nominal peptide antigens and SEB by proliferation in the presence of class II major histocompatibility complex-expressing accessory cells. Although antigen and SEB were comparable in their ability to induce proliferative responses, interleukin 2 (IL-2) production, and IL-2 receptor alpha-chain expression, stimulation with SEB failed to trigger phosphatidylinositol hydrolysis or a rise in the intracellular free calcium ion concentration. Leu3a treatment inhibited antigen-induced proliferative responses of T cells with concomitant suppression of IL-2 production and IL-2 receptor expression. In contrast, SEB-induced responses were unaffected by Leu3a. These findings indicate that the functional consequences of binding (ligation) of conventional antigen and of superantigen with the T-cell receptor are distinct in the context of both signal transduction pathways and participation of CD4 molecules.     

Modulation of T-cell functions in KIR2DL3 (CD158b) transgenic mice.

In humans, a minor subset of T cells express killer cell Ig-like receptors (KIRs) at their surface. In vitro data obtained with KIR(+) alphabeta and gammadelta T-cell clones showed that engagement of KIR molecules can extinguish T-cell activation signals induced via the CD3/T-cell receptor (TCR) complex. We analyzed the T-cell compartment in mice transgenic for KIR2DL3 (Tg-KIR2DL3), an inhibitory receptor for HLA-Cw3. As expected, mixed lymphocyte reaction and anti-CD3 monoclonal antibody (MoAb)-redirected cytotoxicity exerted by freshly isolated splenocytes can be inhibited by engagement of transgenic KIR2DL3 molecules. In contrast, antigen and anti-CD3 MoAb-induced cytotoxicity exerted by alloreactive cytotoxic T lymphocytes cannot be inhibited by KIR2DL3 engagement. In double transgenic mice, Tg-KIR2DL3 x Tg-HLA-Cw3, no alteration of thymic differentiation could be documented. Immunization of double transgenic mice with Hen egg white lysozime (HEL) or Pigeon Cytochrome-C (PCC) was indistinguishable from immunization of control mice, as judged by recall antigen-induced in vitro proliferation and TCR repertoire analysis. These results indicate that KIR effect on T cells varies upon cell activation stage and show unexpected complexity in the biological function of KIRs in vivo.     

Analysis of T-cell subsets in B-cell chronic lymphocytic leukemia: a correlation with the stage of disease

T-cell subsets were determined by the Leu monoclonal antibodies in the peripheral blood and/or bone marrow of 52 patients with B-cell chronic lymphocytic leukemia (B-CLL) not on therapy at the time of study. The diagnosis of B-CLL required that the leukemic cells expressed surface receptors for "la-like" antigen, Fc fragment of IgG, mouse red blood cells (MRBC), C3-coated red cells (EAC), and low density of monoclonal surface immunoglobulin. The Leu-3a+/2a+ ratio was applied to define the balance between the helper/suppressor subsets in the residual T-lymphocytes. Most patients showed a decrease in the Leu-3a+/2a+ ratios at all stages of disease. The decrease in ratio was mainly related to a decrease in the Leu-3a+ T-cell subset. The more advanced stages of B-CLL were associated with lower Leu-3a+/2a+ ratio, higher total white cell and percent lymphocyte counts. There was no correlation between the proportion of EAC or MRBC rosetting cells and stages of B-CLL. This analysis further suggests that B-CLL is an immunosuppressed state that becomes more pronounced in the advanced stages and is characterized by a progressive decrease in the Leu-3a+ (helper) T-cell subset.     

Downregulation of antigen-presenting cell functions after administration of mitogenic anti-CD3 monoclonal antibodies in mice

Antibodies against CD3epsilon are widely used as immunosuppressive agents. Although it is generally assumed that these reagents exert their immunomodulatory properties by inducing T-cell deletion and/or inactivation, their precise mechanism of action remains to be elucidated. Using a murine model, we demonstrate in this report that administration of anti-CD3epsilon antibodies causes the migration and maturation of dendritic cells (DC) in vivo, as determined by immunohistochemical analysis. This maturation/migration process was followed by selective loss of splenic DC, which resulted in a selective inhibition of antigen-presenting cell (APC) functions in vitro. Spleen cells from anti-CD3epsilon-treated animals were unable to productively stimulate naive alloreactive T cells and Th1-like clones in response to antigen, while retaining the ability to present antigen to a T-cell hybridoma and Th2 clones. Anti-CD3epsilon treatment was found to induce a selective deficiency in the ability of spleen cells to produce bioactive interleukin-12 in response to CD40 stimulation. APC dysfunction was not observed when nonmitogenic forms of anti-CD3epsilon antibodies were used, suggesting that splenic DC loss was a consequence of in vivo T-cell activation. Nonmitogenic anti-CD3epsilon monoclonal antibodies were found to be less immunosuppressive in vivo, raising the possibility that APC dysfunction contributes to anti-CD3epsilon-induced immunomodulation. Collectively, these data suggest a novel mechanism by which mitogenic anti-CD3epsilon antibodies downregulate immune responses.     

Autoreactive CD4(+) T-cell clones to beta2-glycoprotein I in patients with antiphospholipid syndrome: preferential recognition of the major phospholipid-binding site

Autoreactive CD4(+) T cells to beta2-glycoprotein I (beta2GPI) that promote antiphospholipid antibody production were recently identified in patients with antiphospholipid syndrome (APS). To further examine antigen recognition profiles and T-cell helper activity in beta2GPI-reactive T cells, 14 CD4(+) T-cell clones specific to beta2GPI were generated from 3 patients with APS by repeated stimulation of peripheral blood T cells with recombinant beta2GPI. At least 4 distinct T-cell epitopes were identified, but the majority of the beta2GPI-specific T-cell clones responded to a peptide encompassing amino acid residues 276 to 290 of beta2GPI (KVSFFCKNKEKKCSY; single-letter amino acid codes) that contains the major phospholipid-binding site in the context of the DRB4*0103 allele. Ten of 12 beta2GPI-specific T-cell clones were able to stimulate autologous peripheral blood B cells to promote anti-beta2GPI antibody production in the presence of recombinant beta2GPI. T-cell helper activity was exclusively found in T-cell clones capable of producing interleukin 6 (IL-6). In vitro anti-beta2GPI antibody production induced by T-cell clones was inhibited by anti-IL-6 or anti-CD40 ligand monoclonal antibody. In addition, exogenous IL-6 augmented anti-beta2GPI antibody production in cultures of the T-cell clone lacking IL-6 expression. These results indicate that beta2GPI-specific CD4(+) T cells in patients with APS preferentially recognize the antigenic peptide containing the major phospholipid-binding site and have the capacity to stimulate B cells to produce anti-beta2GPI antibodies through IL-6 expression and CD40-CD40 ligand engagement. These findings are potentially useful for clarifying the pathogenesis of APS and for developing therapeutic strategies that suppress pathogenic antiphospholipid antibody production in these patients.     

Regulation of the human immune response to HBsAg: effects of antibodies and antigen conformation in the stimulation of helper T cells by HBsAg

The role of accessory cells (antigen-presenting cells) in binding HBsAg in the response of human T cells to this antigen was studied. Antibodies to HBsAg of IgG class increased significantly the amount of HBsAg that was captured and internalized by accessory cells in vitro. On the other hand, antibodies to HBsAg of IgM class or the F(ab')2 and Fab fragments of antibodies to HBsAg of IgG class did not modify the amount of HBsAg associated to these cells. HBsAg that was subjected to various denaturing treatments (acid, organic solvents, urea and heat) was compared for its capacity to react with antibody to HBsAg and stimulate the response of helper T lymphocytes. Results presented here indicate that HBsAg denatured by treatment with formic acid was captured by accessory cells and presented to the T cells much more efficiently than the native HBsAg. These results suggest that the response of helper T lymphocytes to some antigens such as HBsAg can be affected greatly by the presence of antibodies or the antigens' conformation.