Lysis of inducer T cell clones by activated macrophages and macrophage-like cell lines

Altered antigen-presenting capacity of human monocytes after phagocytosis of bacteria

The antigen-presenting and accessory functions of monocytes were studied after phagocytosis of bacteria. Peripheral blood monocytes isolated from mononuclear cells by counterflow elutriation were incubated with suspensions of opsonized bacteria (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, or Salmonella enteritidis) under conditions in which at least 80% of the monocytes engulfed microorganisms. Either the cells were pulsed with antigen (purified derivative of tuberculin or tetanus toxoid) and used as antigen-presenting cells for autologous T lymphocytes or the accessory function of the cells was examined in pokeweed mitogen-activated cultures of T cells. It has been found that phagocytosis of bacteria by monocytes reduces their ability to trigger antigen- and mitogen-induced proliferation. The reduced proliferative response of T lymphocytes was not due to a change of the kinetics of the response or triggering of suppressor mechanisms. Furthermore, antigen processing was not affected much after phagocytosis of bacteria since antigen-pulsed and paraformaldehyde-fixed cells containing bacteria were comparable to control cells in their antigen-presenting capacity. This phenomenon was observed after phagocytosis of both living and dead bacteria and was not correlated to the viability of monocytes, which were more affected after phagocytosis of living bacteria than of dead ones. As a result of phagocytosis of bacteria, reduced expression of CD54, CD14, and HLA-DQ, variable reduction of HLA-DP, CD58, and CD64, and reduced viability of monocytes were observed. In conclusion, phagocytosis of bacteria by monocytes affects their antigen-presenting and accessory functions presumably because of changes in the expression of molecules essential for monocyte-T-cell interactions and reduction of their viability.

Dysregulated expression of the T cell cytokine Eta-1 in CD4-8- lymphocytes during the development of murine autoimmune disease

The development of autoimmune disease in the MRL/MpJ-lpr inbred mouse strain depends upon the maturation of a subset of T lymphocytes that may cause sustained activation of immunological effector cells such as B cells and macrophages. We tested the hypothesis that abnormal effector cell activation reflects constitutive overexpression of a T cell cytokine. We found that a newly defined T cell cytokine, Eta-1, is expressed at very high levels in T cells from MRL/l mice but not normal mouse strains and in a CD4-8- 45R+ T cell clone. The Eta-1 gene encodes a secreted protein that binds specifically to macrophages, possibly via a cell adhesion receptor, resulting in alterations in the mobility and activation state of this cell type (Patarca, R., G. J. Freeman, R. P. Singh, et al. 1989. J. Exp. Med. 170:145; Singh, R. P., R. Patarca, J. Schwartz, P. Singh, and H. Cantor. 1990. J. Exp. Med. 171:1931). In addition, recent studies have indicated that Eta-1 can enhance secretion of IgM and IgG by mixtures of macrophages and B cells (Patarca, R., M. A. Lampe, M. V. Iregai, and H. Cantor, manuscript in preparation). Dysregulation of Eta-1 expression begins at the onset of autoimmune disease and continues throughout the course of this disorder. Maximal levels of Eta-1 expression and the development of severe autoimmune disease reflect the combined contribution of the lpr gene and MRL background genes.

Inhibition of macrophage-induced antigen-specific T-cell proliferation by interferon-gamma

The effects of IFN-gamma on macrophage (M phi)-mediated antigen-specific T-cell proliferation was investigated. A well-defined assay system using purified resident populations of antigen-pulsed peritoneal M phi and immune T cells was used to measure M phi-induced antigen-specific T-cell proliferation. Antibody affinity purified or recombinant IFN-gamma inhibited M phi-induced T-cell proliferation when KLH-pulsed M phi from mice given IFN-gamma prior to KLH were cultured with KLH immune T cells from normal mice. Monoclonal rat anti-IFN-gamma antibody neutralized the inhibitory effect of IFN-gamma. This inhibition of T-cell proliferation occurred despite the fact that these M phi appeared to be activated by IFN-gamma treatment as measured by increased tumoricidal activity. The mechanism for the inhibition was unrelated to class II (Ia) expression, IL-1 secretion, and prostaglandin secretion. These results demonstrate the complex and sensitive role IFN-gamma has in regulating the immune response.

rpt-1, an intracellular protein from helper/inducer T cells that regulates gene expression of interleukin 2 receptor and human immunodeficiency virus type 1

The Rpt-1 (for regulatory protein, T-lymphocyte, 1) gene, selectively expressed by resting but not by activated CD4+ inducer T cells, encodes an intracellular protein (rpt-1, Mr 41,000) that down-regulates gene expression directed by the promoter region of the gene encoding interleukin 2 receptor alpha chain and by the long terminal repeat of human immunodeficiency virus type 1. The data reported here suggest that rpt-1 levels may be inversely correlated with activation of CD4+ T cells and human immunodeficiency virus replication leading to clinical symptoms of the acquired immunodeficiency syndrome.

Simultaneous expression of Ia and cytocidal activity by macrophages, and the consequences for antigen presentation

We have investigated whether the interrelationship of Ia expression and cytotoxicity by macrophages, as the two functions if expressed at the same time, might be counterproductive for T-cell development and function. We report that, under some circumstances, there is a clear dissociation of the two activities, as was demonstrated for both in vitro and in vivo conditions. However, the two functions could also be superimposed. Dissociation or superimposition was determined by (i) the nature of the inducing stimulus, and (ii) by the time-span between stimulation and evaluation. It was found that Ia and tumour killing were mainly expressed by the same macrophage population and, as a result, cytolytic activity, when associated with Ia expression, can be directed against T-cell hybridomas in an antigen-specific manner. The physiological relevance of the dissociation or superimposition of Ia expression and tumour killing by macrophages is discussed.

An early response to lipopolysaccharide is the elicitation of macrophages specialized for antigen degradation with negative regulatory effects on the induction of specific immune responses

The ability of macrophages to catabolize antigens is relevant both as a means to process complex antigens before presentation to T cells and as a way to down-regulate immune responses by destroying the antigenicity of polypeptides. With these considerations in mind, we investigated the regulation of macrophage catabolic activity by lipopolysaccharide (LPS). Catabolic activity was quantitated by following the distribution and molecular form of 125I-labeled surface components of heat-killed Listeria monocytogenes after their uptake by macrophages. We compared the catabolic activity of macrophages from peritoneal exudates of mice injected intraperitoneally with saline or LPS and found that LPS-elicited macrophages displayed a greatly enhanced (threefold) rate of catabolism. This increase in catabolic activity peaked 3 days after LPS injection and slowly declined thereafter, approaching a base-line level after 3 weeks. The enhancement of catabolic activity was under Lps gene control. Macrophages that were elicited 3 days after intraperitoneal injection of LPS rapidly destroyed the antigenicity of bacterial antigens, expressed low levels of Ia molecules, and processed and presented antigen slowly when tested as antigen-presenting cells in vitro. We also showed that an injection of LPS before infection with L. monocytogenes resulted in diminished development of T-cell reactivity to this organism. These results suggest that LPS elicits a macrophage population specialized for antigen degradation functions, with negative regulatory effects on the induction of specific immune responses.

Monoclonal antibodies against a rat leucocyte antigen block antigen-induced T-cell responses via an effect on accessory cells

The MRC OX-45 and OX-46 mouse monoclonal antibodies recognize a rat cell surface glycoprotein of 45,000 MW that is present on a wide variety of haematopoietic cells and on endothelial cells. MRC OX-45 IgG or F(ab')2 blocked the primary mixed lymphocyte response (MLR) and the secondary response of T lymphocytes to the soluble antigen DNP-BGG. In contrast, the antibodies had no effect on the cytotoxic activity of specific (CTL) or non-specific (NK) killer cells or on proliferative responses stimulated by lectins or oxidative mitogenesis. The inhibitory effect was at the level of stimulator cells rather than responders since mouse anti-rat xenogeneic MLRs were inhibited but rat anti-mouse responses were unaffected. However, the effect was not a direct one because inhibition was seen when irradiated spleen cells were used as stimulators but not when cell populations highly enriched for dendritic cells were used. In the latter case, inhibition potentiated by antibody could be restored if a peritoneal cell population enriched for macrophages was added back to the cultures. The inhibitory effects of these monoclonal antibodies seem most likely to be due to potentiation of nonspecific suppression by macrophages.

Antigen presentation by epithelial cells of the rat small intestine. II. Selective induction of suppressor T cells

Columnar epithelial cells (EC) isolated from the rat small intestine can present protein antigen in vitro, inducing proliferation of primed T cells. This system was used to examine the immunoregulatory function of T cells activated by presentation of ovalbumin (OVA) by EC. Rat lymph node T cells, sensitized to OVA in vivo and exposed to EC and OVA in vitro, suppressed the in vitro proliferative response of primed T cells to OVA. The suppression mediated by these modulated T cells (Tmod) was antigen-specific, was restricted during the induction phase by Ia antigens on the EC accessory cells, and was not affected by irradiation of Tmod. The generation of suppressor activity in Tmod was accompanied by an increase in expression of suppressor phenotype. It is suggested that a possible in vivo correlate of this phenomenon may play a role in the induction of suppressor T cells mediating systemic tolerance to dietary antigens.

Influence of beta-endorphin on phytohemagglutinin-induced lymphocyte proliferation and on the expression of mononuclear cell surface antigens in vitro

Recent evidence suggests that opiates can modulate the immune responses. In particular it has been shown that beta-endorphin and morphine are able to depress some T lymphocyte functions in humans. In the present study, experiments were designed to evaluate the effect of beta-endorphin phytohemagglutinin-induced lymphocyte proliferation and determine the mechanism of this action. The ability of naloxone to block the effect of beta-endorphin was also investigated, and the influence of beta-endorphin on the expression of mononuclear cell surface antigens using the OKT3, OKT4, OKT8, anti-HLA-DR and anti-beta 2-microglobulin monoclonal antibodies was evaluated. Phytohemagglutinin-induced lymphocyte proliferation was significantly inhibited by beta-endorphin. This effect occurred when beta-endorphin was added to cells at the beginning of the culture period (30 min before, simultaneously or 30 min after phytohemagglutinin), but not when added after 48 h of incubation. The preincubation of cells with BEP for 1 h, 4 h or 24 h did not affect lymphocyte activation by phytohemagglutinin. A ten-fold excess of naloxone, added to cultures 30 min prior to beta-endorphin, did not block the inhibitory effect. Incubation with beta-endorphin had different effects on each surface antigen tested. The OKT8+ and beta 2-microglobulin+ cells did not show significant variations. The OKT4+ cells significantly decreased, after 4 h of incubation with beta-endorphin, both in mononuclear cell and in purified T lymphocyte cultures and, after 24 h, in mononuclear cell cultures only. The OKT3+ cells decreased, in mononuclear cell cultures only, after 24 h beta-endorphin incubation.(ABSTRACT TRUNCATED AT 250 WORDS)

A subset of Ly-1 inducer T cell clones activates B cell proliferation but directly inhibits subsequent IgG secretion

We find that a fraction of Ly-1+2- inducer T cell clones inhibits differentiation of memory B cells into IgG-secreting plaque-forming cells. Inhibition of secondary antibody responses was not the result of induction of Ly-2+ T suppressors. Instead, inducer cells directly inactivated B cells, requiring an antigen bridge as well as identity at the major histocompatibility complex (I-A) locus. The interaction between the inducer T cell clone and hapten-specific B memory cells results in an early proliferative response and subsequent failure of B cells to secrete antibody in response to T helper cell signals. Possible mechanisms for this novel type of B cell inactivation are explored.

The anatomy of peripheral lymphoid organs with emphasis on accessory cells: light-microscopic immunocytochemical studies of mouse spleen, lymph node, and Peyer's patch

Antigen, lymphocytes, and accessory cells interact within peripheral lymphoid organs to generate immunity. Two cell types have been studied for accessory function in culture: mononuclear phagocytes and nonphagocytic Ia-rich dendritic cells. The monoclonal antibodies which have been used to study isolated murine macrophages (M phi) and dendritic cells (DC) include alpha-macrophage (F4/80, M1/70), alpha-dendritic cell (33D1), alpha-Fc receptor (2.4G2), and alpha-Ia (B21-2) reagents. In this paper, the antibodies have been used to stain accessory cells in cryostat sections of mouse spleen, lymph node, and Peyer's patch. Each organ is known to contain subregions that are rich in either macrophages, B cells, or T cells. We found that the accessory cells in each subregion had a different phenotype. 1) Macrophage-rich regions: Macrophages that lined the site of antigen delivery (marginal zone of spleen, around afferent lymphatics of node, and below the epithelium of Peyer's patch) were stained with M1/70 but not with F4/80. F4/80 was abundant on macrophages in other sites: spleen red pulp, node medulla, and around Peyer's patch efferent lymphatics. 2) B-lymphocyte-rich follicles: Follicular dendritic cells, which retain immune complexes extracellularly, are concentrated on the outer aspect of the germinal center. This region stained strongly with alpha-Fc receptor antibody 2.4G2, but not with M1/70, F4/80, or 33D1. 3) T areas: The interdigitating cells of T areas have been linked to isolated dendritic cells. Irregular Ia-rich cells were distributed uniformly in the T areas of each organ. However, staining with 33D1 was not detected and was restricted to foci of nonphagocytic cells at the spleen red/white pulp junction. F4/80, M1/70 or 2.4G2 also did not stain the T area, except for the region close to splenic central arteries. Therefore the principal surface markers and locations of the candidate accessory cells in murine lymphoid organs are M1/70+ macrophages at the site of antigen entry; F4/80+ macrophages around regions of lymphocyte efflux; germinal center dendritic cells, which may be rich in 2.4G2; and Ia-rich interdigiting cells in the T area.

Binding of antigen in the absence of histocompatibility proteins by arsonate-reactive T-cell clones

Inducer T-cell clones reactive to the p-azobenzenearsonate (arsonate) hapten possess binding sites for radioactive arsanylated proteins, which are not present on clones with other antigen specificities. Binding occurred in the absence of histocompatibility proteins. Binding was specific for the p-azobenzenearsonate hapten, since unconjugated proteins and proteins conjugated to the nonactivating o-azobenzenearsonate hapten neither bound to the clones nor competed binding of radioactive antigen. One of the clones was studied in more detail, using a panel of structural analogs of arsonate conjugated to the carrier protein ovalbumin. All conjugates that activated the clone in the presence of antigen-presenting cells also competed binding of radioactive antigen in the absence of antigen-presenting cells. Nonactivating conjugates did not compete binding. Based on evidence in this and the succeeding paper (Rao et al., accompanying paper), we suggest that these arsonate-binding sites may include the physiological antigen receptors of arsonate-reactive T-cell clones.

Quantitative variation in la antigen expression plays a central role in immune regulation

The analysis of la antigen function has focused primarily on allelic variants of Ia molecules. In this review Charles Janeway and his colleagues discuss evidence that quantitative rather than qualitative variation in Ia antigen expression had a major role in immunoregulation and immunologically mediated disease.

Analogs that compete for antigen binding to an arsonate-reactive T-cell clone inhibit the functional response to arsonate

We have tested several structurally related haptens, conjugated to ovalbumin, for their effect on activation of an inducer T-cell clone reactive to the p-azobenzenearsonate (arsonate) hapten. Low concentrations of some analogs inhibited DNA synthesis and lympkokine production by the clone in response to arsanylated antigen, but not in response to the lectin concanavalin A. Inhibition was specific for this clone, since the response of clones reactive to other antigens was not blocked. Inhibition may result from competition of these analogs with arsonate at a site on the T cell. The effectiveness of blocking by arsonate analogs parallels their ability to bind to a previously described arsonate-binding site on the clone (Rao et al., accompanying paper). We suggest that the binding and blocking assays detect the same physiological arsonate-recognition site on the clone, and hence that the cell-surface arsonate-binding sites we have described mediate its physiological response to antigen.

Activation specificity of arsonate-reactive T cell clones. Structural requirements for hapten recognition and comparison with monoclonal antibodies

We describe clones of hapten-specific inducer T cells from (BALB/c X A/J)F1 mice that respond to the p-azobenzenearsonate hapten conjugated to carrier proteins or directly conjugated to antigen-presenting cells. Some of the clones are also activated by haptens structurally related to arsonate. All activating analogues are recognized by each clone in association with the same major histocompatibility complex (MHC) protein as is arsonate. Weakly activating and nonactivating analogues are immunogenic in D2.GD amd (BALB/c X A/J)F1 mice, since they can effectively activate primed lymph node cells or long-term hapten-reactive cell lines. Hence the specificities of these clones may reflect their intrinsic recognition of arsonate and its analogues, rather than more efficient presentation of certain analogues than of others by antigen-presenting cells, or differential recognition of associated MHC epitopes by the clones. We compare the activation specificities of the clones with the binding specificities of monoclonal antibodies to arsonate, and discuss structural features of the analogues that may be important for activation and binding. Our results suggest that a site (or subsite) on arsonate-reactive T cell clones may interact directly with hapten, and may be experimentally separable from the site (or subsite) for MHC determinants.