Suppression of hapten-specific antibody response by carrier-specific T cells

The Pivotal Role of Regulatory T Cells in the Regulation of Innate Immune Cells

The distinction between innate and adaptive immunity is one of the basic tenets of immunology. The co-operation between these two arms of the immune system is a major determinant of the resistance or susceptibility of the host following pathogen invasion. Hence, this interactive co-operation between cells of the innate and adaptive immunity is of significant interest to immunologists. The sub-population of CD4⁺ T cells with regulatory phenotype (regulatory T cells; Tregs), which constitute a part of the adaptive immune system, have been widely implicated in the regulation of the immune system and maintenance of immune homeostasis. In the last two decades, there has been an explosion in research describing the role of Tregs and their relevance in several immunopathologies ranging from inflammation to cancer. The majority of these studies focus on the role of Tregs on the cells of the adaptive immune system. Recently, there is significant interest in the role of Tregs on cells of the innate immune system. In this review, we examine the literature on the role of Tregs in immunology. Specifically, we focus on the emerging knowledge of Treg interaction with dendritic cells, macrophages, neutrophils, and γδ T cells. We highlight this interaction as an important link between innate and adaptive immune systems which also indicate the far-reaching role of Tregs in the regulation of immune responses and maintenance of self-tolerance and immune homeostasis.

Special regulatory T-cell review: A rose by any other name: from suppressor T cells to Tregs, approbation to unbridled enthusiasm

In the early 1970s a spate of papers by research groups around the world provided evidence for a negative regulatory role of thymus-derived lymphocytes (T cells). In 1971, Gershon and Kondo published a seminal paper in Immunology entitled 'Infectious Immunological Tolerance' indicating that such negative regulation could be a dominant effect that prevented otherwise 'helpful' T cells from mediating their function. Over the next decade, suppressor T cells, as these negative regulatory cells became known, were intensively investigated and a complex set of interacting cells and soluble factors were described as mediators in this process of immune regulation. In the early 1980s, however, biochemical and molecular experiments raised questions about the interpretation of the earlier studies, and within a few years, the term 'suppressor T cell' had all but disappeared from prominence and research on this phenomenon was held in poor esteem. While this was happening, new studies appeared suggesting that a subset of T cells played a critical role in preventing autoimmunity. These T cells, eventually dubbed 'regulatory T cells', have become a major focus of modern cellular immunological investigation, with a predominance that perhaps eclipses even that seen in the earlier period of suppressor T cell ascendancy. This brief review summarizes the rise and fall of 'suppressorology' and the possibility that Tregs are a modern rediscovery of suppressor T cells made convincing by more robust models for their study and better reagents for their identification and analysis.

Tolerance, suppression and the fetal allograft

In solid organ transplantation the recipient immune system recognises foreign alloantigens expressed by the graft. This results in an immune attack of the transplanted organ leading to rejection, which can be prevented only by therapeutic immunosuppression. During pregnancy the fetus should also be rejected by the maternal immune system, since it expresses antigens derived from the father. Whilst the immune system retains the ability to respond to foreign antigen, tolerance mechanisms ensure that inappropriate responses against self-antigen are prevented. Maternal immune aggression directed against the fetus is partly inhibited by peripheral tolerance mechanisms that act locally to deplete cells capable of attacking the fetus. Other local mechanisms inhibit the pathways that cause tissue damage after immune activation. Recent studies in mice and humans indicate that the maternal immune system undergoes a more systemic change that promotes materno-fetal tolerance. Naturally occurring regulatory T cells, which are commonly associated with maintaining tolerance to self-antigens, can also suppress maternal allo-responses targeted against the fetus. We review the mechanisms that mediate materno-fetal tolerance, with particular emphasis on changes in regulatory T cell function during pregnancy and discuss their implications.

Analysis of antigen-specific, Ig-restricted cell-free material made by I-J+ Ly-1 cells (Ly-1 TsiF) that induces Ly-2+ cells to express suppressive activity

A set of T cells defined by a unique profile of cell surface alloantigens (phenotype Ly-1+2-; Qa-1+; I-J+) produces biologically active cell-free material(s) (Ly-1 TsiF) which induces another T cell set (cell surface phenotype Ly-1,2+; I-J/; Qa-1+) to participate in the suppression of primary immune responses to heterologous erythrocytes. The suppression is specific for the inducing antigen, and the Ly-1 TsiF binds antigen in a specific way. The activity of Ly-1 TsiF can be removed by anti-I-J immunosorbents and will not be expressed if the functional producer and acceptor cells do not share gene products that are encoded in or are tightly linked to the VH portion of the Ig complex. There is no requirement for the Ly-1 TsiF and its acceptor cell(s) to share major histocompatibility complex gene products. Thus, for optimal induction of antigen-specific suppression by cell-gree materials from Ly-1 T cells, three necessary conditions must be met: (a) antigen recognition by Ly-1 TsiF; (b) the expression of I-J gene products and (c) identify of VH-linked Ig locus gene products (or other products influenced by those genes) on both the inducer molecule and its acceptor cell. The role of the Ig-linked restriction is particularly intriguing, and its possible meaning is considered in detail.

The induction of carrier-specific helper cell tolerance in presensitized rats

Lewis rats rendered tolerant to sheep IgG (SGG) show a markedly reduced antibody response to the 2,4,6-trinitrophenyl (TNP) hapten when later challenged with TNP-SGG. We have previously shown that this effect is due to functional unresponsiveness in the carrier SGG-specific helper T cell population. In this paper we demonstrate that induced helper cell tolerance is also maintained through a secondary immunogenic challenge. Furthermore, rats which are primed to the carrier SGG prior to tolerance induction also show a markedly reduced anti-TNP response upon secondary immunogenic challenge with TNP-SGG. The ability to specifically suppress a secondary response in this manner was found to be relatively long lasting, since rats showed reduced responsiveness when the secondary challenge was delayed for up to 4 weeks after tolerance induction. In addition, rats primed to the hapten (TNP) prior to carrier (SGG) tolerance induction also showed a marked reduction in anti-TNP antibody following challenge with TNP-SGG. These findings imply that helper cell tolerance can be induced in rats even after priming of carrier-specific (SGG) helper cells, or hapten-specific (TNP) B cells. These results parallel our other published findings that IgE responses in presensitized rats can be overcome by helper cell tolerance.

Suppressor cell induction in vitro. I. Kinetics of induction of antigen-specific suppressor cells

The induction of antigen-specific suppressor cells in vitro, using high concentrations (100 mug/ml) of keyhole limpet hemocyanin (KLH) in Marbrook flasks is described. Spleen and cortisone-resistant thymocytes were the richest source of suppressor cell precursors, compared to lymph node cells, peripheral blood lymphocytes or thoracic duct lymphocytes. Suppressor cells induced with KLH only suppressed KLH-reactive helper cells, and not B cells or helper cells of other specificity. The suppressor cells were T cells, as judged by their sensitivity to anti-Thy-1.2, heterologous anti-T, but not anti-B antisera.

Idiotype suppression. II. Amplification of a suppressor T cell with anti-idiotypic activity

Guinea pig IgG2 anti-idiotypic antibody (aId2) against the strain A/J antibody A5A has a suppressive effect on the expression of the A5A idiotype in adult A/J mice immunized with Group A streptococci. High doses of aId2 cause an immediate but transient suppression, whereas low doses of aId2 result in a delayed but chronic suppression which lasted for more than 1 year without any indication of recovery. Chronic suppression is transferred by as few as 10(5) spleen cells, but an interval of 6 weeks after transfer is required for completion of suppression. The suppressive capacity of aId2-induced suppressor cells was virtually inexhaustable in 4 consecutive transfers spaced at 3 month intervals. The suppressor cell is a T cell which adheres to histamine-rabbit serum albumin-Sepharose 2B columns.

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

Passively transferred thymocytes and spleen cells from donors primed with keyhole limpet hemocyanin (KLH) exerted differential suppressive effect on IgM and IgG antibody responses of syngeneic recipients immunized with DNP-KLH depending primarily on the time when KLH-primed cells were transferred. This was demonstrated by the decrease in the numbers of DNP-specific direct and indirect PFC in the spleen of the recipients given KLH-primed cells at different times during primary and secondary immunization. Whereas the cell transfer simultaneously with or 2 days after the primary immunization produced only slight suppression of the peak IgM antibody response, it caused profound suppression of late IgM and IgG antibody responses. By contrast, the cell transfer 3 days after the immunization produced immediate suppression of the ongoing IgM antibody response resulting in its earlier termination, while being unable to prevent the induction of IgG antibody response. KLH-primed cells could moderately suppress the secondary anti-DNP antibody response, in which IgG antibody response was found to be slightly more sensitive than IgM antibody response to the suppressive influence of KLH-primed cells. The suppressive effect of the KLH-primed spleen cells was completely eliminated by the in vitro treatment of the cells with anti-theta and C before cell transfer, indicating that cells responsible for the suppression are, in fact, T cells. The suppression of DNP-specific antibody response by KLH-primed T cells was achieved only if the recipients were immunized with DNP-KLH but not with DNP-heterologous carrier, suggesting that direct interaction between T and B cells is necessary for the suppression of the antibody response. It is concluded that susceptibility of B cells to the specific suppressive influence of T cells is inherently different depending on the differentiation stage of B cells and on the immunoglobulin class they are destined to produce.

Dual regulatory role of the thymus in the maturation of immune response in the rabbit

Rabbits thymectomized in early adulthood produced more antihapten antibody than sham-thymectomized controls after hyperimmunization with 2,4-dinitrophenyl bovine gamma globulin (DNP-BGG). The average associated constant of anti-DNP antibody produced by thymectomized animals was more than 10 times higher than that of the controls. Similar effects were obtained by extensive treatment of rabbits with antithymocyte serum (ATS) before and during the immunization with DNP-BGG. The results indicated that relative diminution of thymus-derived lymphocytes (T cells) resulted in a stimulation of antibody-forming cells with a higher affinity. On the other hand, preimmunization of rabbits with different doses of BGG caused either enhancement or suppression of the hapten-specific antibody response, depending on the priming dose of BGG. The suppressed antibody response was always associated with a marked decrease in the antibody affinity. If rabbits were partially tolerized with a large dose of soluble BGG, some of the animals produced little antibody against hapten (DNP) coupled to this carrier, and the affinity of produced antibody was low. However, other rabbits tolerized with BGG produced large amounts of anti-DNP antibody upon hyperimmunization with DNP-BGG, whose affinity was only slightly lower than that of the control. These results can be harmonized if it is assumed that the thymus plays an important role in the maturation of the immune response. It is postulated that T cells, in numbers ordinarily available, would first assist in the proliferation of antihapten antibody-forming cell precursors already selected by antigen, thus accounting for the rapid increase of antibody affinity in the early stage of immunization. However, after a larger number of carrier-specific T cells are made in response to continued immunization, these would suppress antibody-forming cells. The suppression would be greater for cells with higher affinity for antigen, resulting in a decrease in antibody affinity. This postulate explains preferential stimulation and suppression of cells having higher affinity receptors under circumstances in which T cell are relatively depleted or overstimulated, and further permits an explanation for the decrease of antibody affinity after long-term immunization.