Selective roles of thymus-derived lymphocytes in the antibody response. I. Differential suppressive effect of carrier-primed T cells on hapten-specific IgM and IgG antibody responses

Under-explored experimental topics related to integral mycobacterial vaccines for leprosy

Many leprosy vaccine studies have utilized live or killed whole mycobacteria, such as Bacille Calmette-Guérin, Indian Cancer Research Center (ICRC) bacilli and Mycobacterium w either alone or in combination with killed Mycobacterium leprae. For Bacille Calmette-Guérin, the vaccine dose is generally that which gives the largest delayed-type hypersensitivity response with minimal side effects. The doses of other integral mycobacterial vaccines appear to be arbitrarily chosen. Hypotheses governing immunologic responses to complex antigens predict that the doses used may be too high, resulting in protection of some individuals and increasing the susceptibility of other individuals to leprosy. The natural history of an individual's prior exposure to environmental mycobacteria will affect the outcome of protective vaccination using a given dose of mycobacterial vaccine in the individual.

Characterization of antigen-binding and MHC class II-bearing T cells with suppressive activity in response to tolerogenic stimulus

Antigen specific non-responsiveness is generally developed through clonal deletion, anergy, and suppression. The term "suppression" is being considered as a functional immune deficit that can be adoptively transferred by regulatory/suppressor T cells. Following tolerance induction protocols the aim of the present study was to characterize the T cells involved in antigen-specific suppression. After defining the immunogenic and tolerogenic protocols in vitro and in vivo, it was shown that CD90(+) cells from tolerogenic mice were able to reduce specific antibody production when adaptively transferred to immunized mice. These cells were shown to highly express CD25 and Foxp3, co-localizing with CD4 and MHC class II antigens (MHCII), while a small percentage of these cells (8-14%) was binding free antigen. Further isolation of CD90(+)MHCII(+) and CD90(+)HSA(+) from mice having received the tolerogenic treatment and adaptive transfer to immunized mice showed that CD90(+)MHCII(+) cells were able to suppress antigen-specific response only when transferred along with the second antigenic challenge, while CD90(+)HSA(+) cells were suppressive only when given along with the first antigenic challenge. The suppressive effect of these two sub-populations could also be obtained in in vitro spleen cell proliferation assays in response to the HSA antigenic stimulus. Both in vitro and in vivo tolerogenic treatments were shown to correlate with soluble MHCII production in culture supernatants or serum respectively. Increase of MHCII in the serum could only be detected upon adaptive transfer of CD90(+)HSA(+) cells, whereas transfer of CD90(+)MHCII(+) cells resulted in increased levels of IL-10 and IFN-γ in the serum. These results defined at least two different levels of suppression, one during the onset which was antigen-specific and MHC restricted, and another non-specific at the end of an immune response.

Regulatory T cells and their role in rheumatic diseases: a potential target for novel therapeutic development

Regulatory T cells have an important role in limiting immune reactions and are essential regulators of self-tolerance. Among them, CD4+CD25high regulatory T cells are the best-described subset. In this article, we summarize current knowledge on the phenotype, function, and development of CD4+CD25high regulatory T cells. We also review the literature on the role of these T cells in rheumatic diseases and discuss the potential for their use in immunotherapy.

The dynamic co-evolution of memory and regulatory CD4+ T cells in the periphery

Whereas memory T cells are required to maintain immunity, regulatory T cells have to keep the immune system in check to prevent excessive inflammation and/or autoimmunity. Both cell types must be present during the lifetime of the organism. However, it is not clear whether both subsets are regulated in tandem or independently of each other, especially because thymic involution severely restricts the production of T-cell populations during ageing. In this Opinion article, we discuss recent evidence in both mice and humans that supports the hypothesis that some CD4(+)CD25(+)FOXP3(+)regulatory T cells can differentiate from rapidly proliferating memory T cells in the periphery.

Molecular dynamics and protein function

A fundamental appreciation for how biological macromolecules work requires knowledge of structure and dynamics. Molecular dynamics simulations provide powerful tools for the exploration of the conformational energy landscape accessible to these molecules, and the rapid increase in computational power coupled with improvements in methodology makes this an exciting time for the application of simulation to structural biology. In this Perspective we survey two areas, protein folding and enzymatic catalysis, in which simulations have contributed to a general understanding of mechanism. We also describe results for the F(1) ATPase molecular motor and the Src family of signaling proteins as examples of applications of simulations to specific biological systems.

T-regulatory cells: are we re-discovering T suppressors?

Regulatory T cells are shown to originate form the thymus and their role is to maintain self-tolerance to intra-thymic as well as extra-thymic self-antigens. Their mode of action, using in vivo and in vitro systems, has led to different conclusions as to the need of cell-cell interactions or regulation upon suppressive cytokines. The more we study regulatory T cells the more we find similarities to the old notion of the suppressor T cell network. The limited knowledge in molecular technology in the early 70s and 80s discouraged investigators to further scrutinize the issue and the terms T suppressors and contra-suppressors that were coined back then have been forgotten over the years. It is now time to remember the work of these investigators and attempt to explain their findings using the current knowledge and technology.

Antibody affinity maturation: the role of CD8+ cells

The cellular control of antibody affinity maturation has been studied in mice genetically selected for their failure to demonstrate an increase in affinity following immunization (low-affinity N/M mice). Depletion of CD8+ cells in low N/M mice by thymectomy and/or anti-CD8 antibody treatment resulted in these animals acquiring the ability to mount an anti-DNP response of progressively increasing affinity. This indicates that CD8+ cells play an important regulatory role in the cellular interactions underlying the process of affinity maturation. In addition, evidence is presented which suggests that the route of immunization may also be critical in determining the affinity of antibody produced.

Experimental zinc deficiency: effects on cellular responses and the affinity of humoral antibody

Mice genetically selected for the production of either high- or low-affinity antibody were fed on diets sufficient or deficient in zinc. The effect of zinc deficiency on immune responses in these animals was analysed in terms of cell-mediated responses and the levels and affinity of antibody produced in response to immunization with T-dependent and T-independent antigens. In comparison with animals fed zinc-containing diets, mice fed zinc-deficient diets had reduced numbers of T cells and T-cell subsets, reduced proliferation to mitogens and specific antigen, and a decreased production of interleukin 2 (IL-2), but the number and affinity of IL-2 receptors were not affected. Furthermore, zinc-deficient animals produced reduced levels of antibody to the T-dependent antigen DNP-human serum albumin, but the affinity of this antibody was significantly elevated compared with that produced by zinc-sufficient animals. However, zinc deficiency had no effect on the levels and affinity of antibody produced to the T-independent antigen DNP-ficoll.

Prostaglandin E2 production is enhanced in mice genetically selected to produce high affinity antibody responses

Spleen cells from mice selectively bred to produce high affinity antibody responses to protein antigens (HI) had reduced responses to both T and B cell mitogens when compared to those from mice selectively bred to produce low affinity (LO) responses. The reduced response by spleen cells from HI mice was partially reversed by the addition of indomethacin in vitro. Spleen adherent cells from HI mice had increased production of prostaglandin E2 when compared to those from LO mice. In addition, spleen adherent cells from mice which fail to show affinity maturation not only produced lower amounts of PGE2 than those from HI mice but also a decreased proportion of spleen cells adhered to plastic in these mice. To test the possibility that the increased PGE2 production in HI mice was responsible for the production of high affinity antibodies, indomethacin was administered in vivo and resulted in a significant reduction in antibody affinity. The possibility that PGE2 production may control the balance between the TH1 and TH2 cells of Mosmann and Coffman is discussed.

Inhibition of an IgE response by secondary B cells of a different isotype

We found that the synthesis of IgE anti-Ars antibodies is strongly inhibited by the presence of secondary non-IgE-producing cells that are specific for the Ars hapten. Such B cells can be induced by inoculation of a protein-Ars conjugate in CFA. The effect is seen after inoculation of OVA-Ars in CFA followed by KLH-Ars in alum, or, more convincingly, after adoptive transfer of B cells induced by antigen in CFA. Dose-response data indicated that inhibition can be effected by B cells containing noninhibitory numbers of contaminating T cells. Possible synergistic effects of carrier-specific regulatory T cells were ruled out by using a different protein carrier for immunization of donor and recipient mice. The effect was shown to be specific for the hapten used for immunization of donor mice.

Experimental strategies for the study of cellular immunity in renal disease

This overview has examined some of the current experimental options available for the study of cellular immunity in the immunopathogenesis of renal disease. T cell immunity, where it has been examined, seems to have a particularly pivotal role in orchestrating and regulating functional patterns of renal injury. The use of the research methods presented here for the study of cell-mediated interactional events in kidney disease, however, has lagged behind similar efforts in other organ systems. We hope, therefore, this report will serve to stimulate and strengthen further interest in the cell biology of the nephritogenic immune response.

Carrier-specific induction of suppressor cells controlling anti-erythrocyte autoantibody production in mice

Mice immunized with rat erythrocytes develop anti-erythrocyte autoantibodies, distinct anti-rat erythrocyte agglutinins, and suppressor-inducer cells, which regulate the production of autoantibody but not anti-rat erythrocyte agglutinins upon transfer to naive recipients. In this report, we have tried to determine the specificity of the suppressor-inducer cells. CBA/N mice (which express an X-linked genetic B-lymphocyte defect) immunized with rat erythrocytes developed no autoantibodies but normal levels of anti-rat erythrocyte antibodies and suppressor-inducer cells, thereby suggesting that neither idiotypes on autoreactive B cells nor idiotypes on autoantibody itself, stimulate suppressor-inducer cells. In contrast, rat erythrocyte-primed spleen cells suppressed both a primary 2,4,6 trinitrophenyl (TNP) response and anti-erythrocyte autoantibody production (but not anti-rat erythrocyte antibodies) upon transfer to naive recipients and challenge with TNP-rat erythrocytes. It is considered that the suppressor-inducer cells are carrier-specific and that they are not stimulated by idiotypes on either autoantibody or autoreactive B cells.

Limiting dilution analyses for the quantification of cellular immune responses in bovine ostertagiasis

A sensitive limiting dilution analysis (LDA) was used to quantitate the local and systemic cellular immune response of cattle after immunization with keyhole limpet hemocyanin (KLH) and infection with Ostertagia ostertagi. The assay measures the proliferative response of bovine T-cells after in vitro stimulation with antigen. Interleukin 2 activity was supplied by supernates from mitogen-stimulated bovine peripheral blood lymphocytes (PBL) and accessory cell function was in the form of irradiated autologous PBL. The assay measures the response of a single cell and was most easily demonstrated in the lymph nodes draining the site of antigen inoculation. Comparison of cell frequencies and maximal responses generated in conventional proliferative assays showed several differences between the two assays. First, after antigen injection, the highest cell frequencies were seen in the draining lymph nodes within 3 days, and decreased by 10 days post-immunization. In contrast, in mass cultures maximal stimulation was not seen until 7-10 days after injection, but remained high up to 4 weeks after immunization. Second, at 17 days post-infection, a time of eruption of the parasite from the gastric glands, high frequencies of inducible cells were demonstrated by LDA in all lymphoid populations tested. In contrast, low levels of proliferation were seen in mass cultures. The reasons for these differences may include different sensitivities to suppression or more stringent requirements for specificity between the two assays. Finally, it was found that immunologically naive calves have relatively high frequencies of Ostertagia-specific cells in PBL, and that after infection these frequencies decrease. These results indicate either active suppression of the potential anti-Ostertagia response or an extra-vascularization of these cells to the site of infection.

Features of KLH-induced suppression in vivo: characterization of two pathways of suppression

Keyhole limpet hemocyanin (KLH) given at high dose (4 mg ip) in mice induced a state of unresponsiveness related to the activation of suppressor T cells. An early pathway of suppression is observed within the first 24 hr following KLH injection and is characterized by its cyclophosphamide (CPM) sensitivity and by the specificity of its effector phase, at the level of KLH helper T cells. A late pathway of suppression occurs at Day 3 following KLH injection and is characterized by its CPM resistance and the nonspecificity of its effector phase acting at the B-cell level. Indeed the anti-FLu antibody response to FLu Ovalbumin or thymus-independent antigen FLu LPS were found altered when these antigens were given with TNP KLH. These two pathways of suppression were found to last 8 months. These results suggest that KLH can trigger in an independent manner two pathways of suppression characterized by different CPM sensitivity and different target cells.

Antibody affinity maturation in selectively bred high and low-affinity mice

The affinity of serum antibodies produced by selectively bred lines of mice [high affinity, low affinity, low nonmaturing (N/M)] injected with T-dependent [human serum albumin (HSA), dinitrophenylated bovine gamma-globulin (DNP-BGG)] and T-independent (DNP-Ficoll) antigens in saline and adjuvant has been determined. The lines of mice differ significantly in the affinity of antibody produced to T-dependent antigens injected in saline but not to the T-independent antigen. Unlike mice of the high and low-affinity lines, low-affinity N/M mice failed to show affinity maturation to HSA and DNP-BGG injected in Freund's incomplete adjuvant. However, low-N/M mice responded to DNP-Ficoll injected in adjuvant by the production of antibody of affinity comparable to that produced in the other lines and with a similar maturation in affinity. Carrier priming resulted in the suppression of anti-hapten antibody affinity in all lines but low-N/M mice showed significantly greater suppression late in the response to challenge. Low doses of cyclophosphamide produced a significant increase in affinity in low-N/M mice. These results suggest that the failure of low-N/M mice to show affinity maturation results from increased suppressor T cell activity. The availability of the selectively bred mice provides a useful model for the detailed study of the cellular basis of the control of antibody affinity maturation.

Inhibition of lymphocyte proliferation by free fatty acids. III. Modulation of thymus-dependent immune responses

Free fatty acids (FFA) were tested for their effects on in vitro thymus-dependent (TD) and thymus-independent (TI) immune responses. Murine T cells proliferating in one-way mixed leucocyte reactions (MLR) were extremely sensitive to inhibition by exogenous stearic acid (18:0) but were only moderately affected by oleic acid (18:1). T-cell proliferation was suppressed when 18:0 was added as late as 44 hr after allogeneic stimulation, but sensitivity to 18:1 was limited to the first 30 hr of culture. The inhibitory effects of 18:0, but not 18:1 were potentiated by concomitant T-cell activation and under such conditions the effects of 18:0 were irreversible within 5 hr. The two fatty acids were additionally tested for their effects on the anti-hapten antibody-secreting cell responses to TD and TI antigens. Both 18:0 and 18:1 inhibited the primary antibody response elicited by a TD antigen (TNP-KLH) but neither fatty acid significantly affected the primary antibody response to a TI antigen (TNP-LPS). Following in vivo immunization with TNP-KLH, isolated spleen cells were challenged with the same antigen in vitro in the presence of FFA. Whereas 18:1 had little effect on the secondary immune response, the addition of 18:0 led to a 3-4-fold increase in the number of anti-TNP plaque forming cells. Further studies showed that TNP-KLH-induced T cell proliferation was potently inhibited by 18:0 but 18:1 had no effect. These results suggest that an inhibition of T-cell proliferation is the primary way in which 18:0 modulates TD immune responses in vitro. By contrast, 18:1 appears to inhibit primary antibody responses and MLR via alternative mechanisms.

Repertoires of T cells directed against a large protein antigen, beta-galactosidase. II. Only certain T helper or T suppressor cells are relevant in particular regulatory interactions

11 cyanogen bromide (CB) peptides, comprising 70% of the large protein, Escherichia coli beta-galactosidase (GZ), were studied for their ability to induce T suppressor (Ts) cells capable of strongly suppressing the in vitro anti-fluorescein (FITC) response to GZ-FITC. Only CB-2 (amino acid residues 3-92) and CB-3 (residues 93-187) were found to bear such Ts-inducing epitopes. In examining the specificity of T helper cell (Th) targets susceptible to CB-2 and CB-3-specific Ts, it appeared that only nearly Th targets could be suppressed. Thus, CB-10-primed Th were not suppressed by either Ts; even CB-3-primed Ts did not suppress CB-2-specific Th, although CB-2-specific Ts were effective. Furthermore, analysis of the suppression pattern revealed a hierarchical use of potential epitopes on native GZ in triggering functional regulatory T cells. A dominant Th epitope near the amino terminus of GZ tops a hierarchy of potential Th, most of which are never engaged. The dominant determinant seems to exist on the peptide CB-2-3 (residues 3-187), and presumably is destroyed by its cleavage at Met 92; the Th cells that it induces are suppressible by each of the Ts-inducing peptides. In the GZ system, where the native antigen is quite large, the interactions between Th and Ts are highly circumscribed. This may be attributable to the topology of antigen fragments produced during processing; any relevant fragment must bear at least a Ts- and Th-reactive determinant to permit intercellular regulation. A final implication of these results is that, not only does the existence of a Th-inducing determinant depend on its being an appropriate distance from a B cell epitope, but the existence of Ts-inducing determinants likewise depends on the existence of a neighboring Th-B cell association.

Sequential development of helper and suppressor functions, antibody titers and functional avidities to a streptococcal antigen in rhesus monkeys

Sequential development of antibody titer, functional avidity, helper and suppressor activities were investigated in rhesus monkeys. These were immunized with a single dose of 0.1 microgram to 10 mg of a streptococcal protein antigen (SA) in aluminium hydroxide. The IgG antibody titers followed the classical pattern first established in mice, of high-dose and low-dose tolerance with intermediate doses of immunity. This was correlated with a similar pattern of functional avidity of IgG antibodies, as measured by a dissociation assay. Helper and suppressor functions were assayed in parallel by inducing the corresponding factors from monkey lymphocytes in Marbrook flasks and testing the factors which cross the species barrier in cooperative cultures with CBA mouse spleen B cells. A progressive modulation of helper and suppressor activities was elicited by the increasing doses of SA, during the initial 28 days after immunization. Thus, dominant suppressor with minimal helper activity, IgG antibody titer and functional avidity were elicited by 0.1 microgram SA. However, 1 or 10 micrograms SA induced dominant helper with minimal or transient suppressor activity and high IgG antibody titers and functional avidity. Somewhat intermediate responses were elicited by 100 micrograms SA, but 1 mg and especially 10 mg SA induced dominant suppressor and minimal helper activity, with low IgG antibody titers and functional avidities. When the immune response was established, about 28 days after immunization, the intermediate dose of SA elicited IgG antibodies with high titer and functional avidity, high T cell helper but low suppressor activities. In contrast, both high- and low-dose SA induced partial tolerance, with low IgG antibody titer, functional avidity and T cell helper activity. These studies suggest cyclical development of helper and suppressor functions during the 4 weeks after immunization. The emergence of a dominant helper or suppressor function is antigen dose dependent.

Study of cellular immunity in experimental autoimmune hepatitis in mice

This study was undertaken to produce experimental autoimmune hepatitis in mice, and to examine the role of liver specific lipoprotein (LSP), if any, and of cellular immunity in such a model. After immunization of three strains of mice (C57BL/6, C3H/He and BALB/c) with syngeneic crude liver proteins, most prominent liver changes histologically mimicking human hepatitis were produced in the liver of C57BL/6 (B6) mice. Antigenic and immunogenic activity of LSP in the crude liver proteins was decreased by the treatment of freezing and thawing, and the recovery of the antigenic activity seemed to correlate with the susceptibility of immunized mice to the induction of liver damage. Autoantibody against LSP was demonstrated in the serum of immunized B6 mice, but not in the sera of other strains after immunization. It was also found that EDTA contained in the buffer used for purification of LSP distinctly suppressed lymphocyte activity in vivo and in vitro. With the use of EDTA free LSP, it was shown that spleen cells of immunized B6 mice (especially of T cell enriched fraction) had a high reactivity studied by lymphocyte transformation test. Further examination showed that EDTA free LSP could induce mild liver lesions and lymphocyte reactivity against LSP, although neither histological change nor lymphocyte reactivity was found in the liver of B6 mice immunized with EDTA containing LSP.

Adoptive transfer of immunity by spleen cells from LSA-lymphoma mice cured by BCNU

BCNU treatment of advanced LSA lymphoma, a poorly antigenic tumor of syngeneic C57BL/ym mice, produced large numbers of cured mice which were highly immune against further LSA tumor challenges. Spleen cells from cured mice were transferred into normal naive mice in close temporal relationship to the injection of 10(3) LSA cells and showed that during a period of two days before to one day after tumor injection, the MST and per cent tumor takes could be greatly modified. Activity was only weakly present in bone marrow or thymus cells but mixtures of these cells with or without added spleen cells were effective. In 400 rad sublethally irradiated mice it was also found that transferred spleen cells prevented progression of tumor, and resistance was permanent. This indicates that all elements of tumor recognition, affector and effector limbs of immune response were present in the adoptively transferred spleen cell population.

Regulation of macrophage phagocytosis of syngeneic erythrocytes by T-cell subsets from NZB mice: differential effects of T cells from young and old mice

The regulation of syngeneic erythrophagocytosis (EP) by macrophages (M phi) harvested from young and old NZB mice was examined by spectrophotometric assay and morphological observation. Peritoneal exudate M phi from young NZB mice weakly ingested syngeneic red blood cells (RBC). T cells derived from old NZB mice accelerated ingestion of RBC by young M phi. On the contrary, T cells from young NZB mice suppressed EP by young T cells appeared clearly when they were added to M phi derived from old mice, which ingested syngeneic RBC actively without help by old NZB T cells. Namely, such an active EP by old M phi was completely suppressed when they were incubated with young T cells. Simultaneous addition of both young and old T cells to either young or old NZB M phi with RBC suppressed the EP. Pretreatment of young T cells with anti-Lyt 1.2 antibody and complement (C) made the suppressive activity prominent, and preincubation with anti-Lyt 2.2 and C eliminated the suppressive activity, but gave rise to the enhancing activity. Young T-cell homogenates added to younger or old M phi together with RBC did not reveal suppressive activity for EP, and on the contrary facilitating activity appeared predominantly. Young and old T-cell homogenates added together to young M phi did not suppress EP. The largest of T-cell-factor accelerating EP was M phi, but not RBC. M phi with active EP belong to Ia-bearing subpopulations.

Assessment of T lymphocyte responses induced by parasite antigens

Recently developed procedures for the isolation and continuous growth in vitro of T lymphocytes can be used to extend our knowledge of cellular immune responses elicited by parasitic infections. These procedures are adaptable to the study of both the inductive and effector phases of T cell responses. The inductive phase of T cell responses is measured by assessing the level of blastogenesis induced in antigen-primed lymphocyte populations by parasite antigens. The development of limiting dilution analyses and procedures for the repeated in vitro restimulation of such cells have allowed for the quantitation of blastogenic responses, and for the isolation of antigen-reactive T cells. The effector phase of T cell responses is assessed by assays that detect either, cytolytic activity of the antigen-responsive cells, the secretion of lymphokines by the responding cells, or specific or non-specific T cell mediated immunosuppression.

Clinical significance of immunoglobulin-secreting cells in the peripheral blood in patients with multiple myeloma

Immunoglobulin-secreting cells were enumerated in the peripheral blood of 31 patients with multiple myeloma, nine patients with so-called benign monoclonal gammopathy, and ten patients with polyclonal hypergammaglobulinaemia or idiopathic hypogammaglobulinaemia. Immunoglobulin-secreting cells were detected by a haemolytic plaque assay using protein-A-coated erythrocytes in the presence of class- or type-specific rabbit anti-human immunoglobulin antisera. In about two-thirds of patients with multiple myeloma, cells secreting the same light-chain isotype of their serum M-protein increased in number, whereas this was not the case in the patients with so-called benign monoclonal gammopathy. Follow-up studies of immunoglobulin-secreting cells in multiple myeloma revealed that these cells increased or decreased, correlating with the severity of the disease, and alterations were more rapid than other clinical features. This plaque assay is therefore useful in evaluating the response to chemotherapy in patients with multiple myeloma.

Differential effects of glucocorticosteroids on the functions of helper and suppressor T lymphocytes

The effects of dexamethasone (Dex) on the functions of antigen-primed helper and suppressor T cells were studied in humoral immune responses in vitro. In doses equivalent to elevated physiologic concentrations, the suppressor T cell activity was abolished. In contrast, the helper T cell function was resistant to even pharmacologic concentrations of Dex. The apparent steroid resistance of the helper T cells was found to be mediated by the products of activated macrophages. While macrophage factors protected helper T cells from steroid inhibition, they did not prevent the effects of Dex on suppressor T cells. Because bacterial cell wall and membrane components are potent inducers of the factors that mediate steroid resistance of helper T cells, the combination of physiologically elevated levels of steroids and macrophage factors during acute infections may function to facilitate the expression of host immunity. However, the persistance of these conditions, as in chronic inflammation, may also contribute to the pathogenesis of autoimmunity by perturbing the balance of immune regulation by helper and suppressor T cells.

Differential inhibition by azathioprine and 6-mercaptopurine of specific suppressor T cell generation in mice

Doses of 100 mg/kg/day and 55 mg/kg/day of azathioprine (AZ) and 6-mercaptopurine (6-MP), respectively, significantly suppressed anti sheep red blood cell (SRBC) responses in CBA mice, assayed by the complement-dependent cellular cytotoxicity (CDCC) test and by serum titration. Four injections of similar doses of the agents were given to donors of carrier-specific suppressor T cells, generated by two immunizations with SRBC, and transferred to syngeneic recipients sensitized with the TNP hapten on SRBC carrier. Anti-TNP response of the recipients was assayed by the CDCC, using TNP-coated EL4 target cells. Whereas 6-MP, given after or before the second immunization of the donors with carrier SRBC, caused abrogation of suppressor cell activity, equimolar doses of AZ were less inhibitory to suppressor cell generation.

Antigen-specific T-cell factors

Antigen-specific T-cell factors are mediator molecules which are produced by helper and suppressor T cells and which can perform the function of those cells in an antigen-specific manner. They probably play an important part in immunoregulation. The major histocompatibility complex has a controlling influence on their structure and activity, while their antigen-recognition properties may be conferred by immunoglobulin V regions. Interest in the factors derives from three related areas of research, namely (i) the problem of T-cell recognition of antigen; (ii) the mechanisms of cellular interactions in antibody production and cell-mediated immunity; and (iii) the genetic control of immune responses. This review discusses the literature up to June 1980 on their production, structure, genetic restriction and mechanism of action.

In vivo cyclic change in B-lymphocyte susceptibility to T-cell control

The humoral response to hapten-protein conjugates is an invaluable model for dissecting the cellular elements of lymphocyte cooperation, and the Mitchison secondary adoptive transfer system provides convincing evidence of cooperation between hapten-specific B cells and carrier-specific T cells in the production of anti-hapten antibody. Recently, attention has focused on the role of suppressor T cells in the regulation of antibody production. Several workers have shown that carrier-priming may, in some instances, suppress a subsequent hapten antibody response, both in vivo and in vitro. This effect is attributed to a suppressor T-cell population, generated during the initial phase of the immune response. Gershon and co-workers have postulated that such suppressor T cells function in a feedback regulatory loop to limit the duration of an immune response. We have examined the suppressive effect of carrier immunization in a secondary anti-hapten response in vivo and demonstrate a cyclic change in susceptibility of memory B cells to T-help and suppression. Such variation presents a severe restriction to any model of feedback control by suppressor T cells.

Antigen specific T cell factors

Antigen specific helper and suppressor factors have a similar structure, with two major sections, a 'variable region', determining antigen specificity which is likely to be controlled by Immunoglobulin VH genes, with which it shares idiotype and framework determinants. Specific factors also have a 'constant region' which does not vary between strains and minimally between species or with the antigenic specificity of the factors, which are defined by rabbit anti-helper or anti-suppressor antisera. This region determines the biological function of the molecule. Anti-Ia antisera react with factors, but the nature and function of Ia molecules on T cell factors is still unclear. The model of specific factor structure, with C and V regions resembles that of immunoglobulin, and it is thus possible that the C region of factors, like the V region is Ig linked. Because there are multiple T cells, helping and suppressing antibody responses specifically, it seems improbable that all of these cells could interact directly with rare antigen-specific B cells. Thus we propose that macrophage presenting cells are the key to the integration of signals for immune induction and regulation for T and B cells. Since Ir genes have been identified in the macrophage presenting cells interacting with both T and B cells, this suggests that macrophage Ia antigens are of importance in the integration of triggering signals for the lymphoid pool.

Antigen-laden cells in thoracic duct lymph. Implications for adoptive transfer experiments

T cells from thoracic duct lymph of donor rats suppress the adoptive secondary response to human serum albumin (HSA). The original aim of the present investigation was to determine whether these non-immune cells have antigen-specific receptors. Thoracic duct lymphocytes (TDL) were depleted in vivo of antigen-specific T cells (negatively selected) by acutely injecting non-immune donors with HSA at the time of thoracic duct cannulation. Negatively selected TDL were mixed with memory cells (primed TDL from previously immunized donors) and transferred into irradiated recipients to assess whether the suppressive potential had disappeared. Paradoxically, the addition of negatively selected TDL (which were unresponsive to HSA) augmented the adoptive secondary anti-HSA response. Further study showed that the augmented response was mediated by a very small number of cells (∼ 1 in 5000) laden with antigen that appeared in lymph of non-immune donors following HSA injection. These antigen-bearing cells were highly immunogenic and furthermore could overcome the effects of T suppressor cells in vivo. Once antigen laden cells were removed from lymph (by affinity chromatography), however, negatively selected TDL were found to inhibit the adoptive secondary response suggesting that either suppression in this model is non-specific or that antigen-specific suppressor cells are not selected out of the recirculating pool by antigen.

Light chain isotype-associated suppression of normal plasma cell numbers in patients with multiple myeloma: Medical Research Council's Working Party for Leukaemia in Adults and the Oxford Lymphoma Group

The number of plasma cells in the lamina propria of the gut has been assessed in patients with multiple myeloma and other B-cell neoplasms. The total number of these plasma cells was reduced in most patients with myelomatosis and one-third of patients with lymphoplasmacytoid tumours. This reduction was not, however, seen in patients with other neoplasms of B-cell origin, although hypogammaglobulinaemia was common to all groups of patients. The depletion of gut plasma cell numbers was not uniform in myelomatosis patients. They showed selective loss of plasma cells with the same light chain isotype as that produced by the neoplastic clone.

Interaction of subpopulations of murine lymph node lymphocytes in antigen-induced [14C]-thymidine incorporation: T and B cell synergy in the response to antigen

The antigen-induced [14C]-thymidine incorporation of murine lymph node cells (LNC) that were non-adherent (NAD) or adherent (AD) to nylon wool was studied. In contrast to NAD-LNC, AD-LNC responded like unfractionated LNC, and these responses were T lymphocyte dependent. By co-culturing NAD-LNC with subpopulations of AD-LNC the cellular requirements and interactions necessary for maximal incorporation of [14C]-thymidine were determined. A synergistic effect was observed when NAD-LNC and AD-LNC were co-cultured. Synergism was not dependent on T lymphocytes or macrophages in the AD-LNC population but was associated with the B lymphocyte subpopulation. These results indicate that the number of B lymphocytes present in a population of LNC can significantly influence the magnitude of the response to antigen.

Non-specific immunosuppressive effects of mouse spleen extracts in vitro

Cell-free extracts were prepared from the spleens of keyhole limpet haemocyanin (KLH)-primed, ovalbumin (OVA)-primed or unprimed mice, and were shown to suppress non-specifically the secondary antibody response to TNP1000KLH in vitro. Non-specific activity was retained on storage in liquid nitrogen and was not removed by dialysis. These findings are in contrast to those reported elsewhere where it was found that cell-free extracts from the spleens of KLH-primed mice specifically suppressed the IgG response to TNP1000KLH; this discrepancy may well lie in the initial immunological status of the mice used. Nevertheless it is concluded that proper account should be taken of non-specific suppressive effects when studying the activity of cell-free extracts in vitro.

Development of antigen-induced proliferative responsiveness by murine lymph node cells. I. Identification of differences in the in vitro proliferative responses during a first and a second period of responsiveness

The development and course of antigen-induced proliferative responsiveness by murine lymph node cells (LNC) was observed for 16 weeks post-immunization. The initial phase of responsiveness was characterized by antigen-induced proliferative responsiveness in vitro which reached a maximum 3-5 weeks post-immunization and then declined to low levels by 6-8 weeks. Without injection of additional antigen, the initial phase of responsiveness was followed by the development of a second phase of antigen-induced proliferative responsiveness 10-12 weeks post-immunization. These findings suggest that the in vivo development of lymph node lymphocytes capable of a proliferative response to antigen is under some type of modulation which is maximal 6-8 weeks post-immunization. Early in the first phase the proliferative responses to higher concentrations of antigen peaked early in the culture period (days 3-4), whereas responses to the lower concentrations of antigen were optimal after 5-6 days of culture. During the latter half of the first phase, however, peak proliferative responses were made to all the concentrations of antigen on the same day of culture (day 6). In contrast, the responses detected at the beginning and throughout the second phase of responsiveness were characterized by maximum proliferation to all the concentrations of antigen late in the culture period (day 7). These results delineate the temporal requirements for maturation of antigen-induced proliferative responsiveness of murine LNC post-immunization and indicate the time interval when optimal responses may be detected.

Reaginic antibody to contact sensitizing agents. Occurrence of cells which supress IgG and not reagin responses

Mice painted with the contact sensitizing agent picryl chloride produce IgG and reaginic or IgE-type antibody. They concomitanly produce suppressor cells which can inhibit IgG responses of normal mice to picryl chloride. These cells were produced between 3 and 7 days after primary sensitization (skin painting) and were T cells, as evidenced by their sensitivity to anti-theta serum and by their passage through nylon wool columns. Although they inhibited IgG responses they did not significantly change IgE titres. This correlates with a previous observation that repeated painting with picryl chloride increased IgE and not IgG responses.

Regulation of anti-hapten antibody secretion by carrier-specific suppressor T cells

Carrier-primed T lymphocytes can suppress high avidity IgG anti-hapten antibody secretion within 90 min. in vitro if the suppressor and target cells are primed with the same carrier determinants. Suppression seems to be directed to the antibody secreting cell since the effect is rapid and does not depend on macrophages or T cells in the target cell population. Suppression can be blocked by inclusion of soluble carrier in the cell mixture or by treatment of the target cells with anti-carrier antibody or pronase. Moreover, suppression can be augmented by PFC exposure to the soluble hapten-carrier conjugate. Finally, carrier specificity may be altered by preincubation of the target population with a hapten-heterologous carrier before addition of suppressor cells specific for the heterologous carrier. Thus, it is likely that high avidity suppression depends upon immunogen bound to the surfaces of antibody secreting cells which serves as a target for suppressor cells or molecules.