PIBF1 suppresses the ATR/CHK1 signaling pathway and promotes proliferation and motility of triple-negative breast cancer cells.

PURPOSE: This study evaluates the oncogenic role of PIBF1 in triple-negative breast cancer (TNBC). TNBC is considered to have a poorer prognosis than other types of breast cancer and is associated with high risk of recurrence and distant metastasis. Currently, there are no effective therapies for the TNBC patients with distant metastasis due to the lack of targeted therapeutic options. METHODS: The effects of PIBF1 knockdown on the cell viability and motility of TNBC cell lines were investigated. Effects of PIBF1 overexpression on tumorigenicity and cell motility were confirmed using Ba/F3 cell line and xenograft study on BALB/c nude mice. RESULTS: In TNBC cell lines that highly express PIBF1, knockdown of PIBF1 induces apoptosis and suppresses cell viability and motility with activation of the ATR/CHK1 signaling pathway. Moreover, the oncogenic function of PIBF1 was confirmed using the Ba/F3 cell line. CONCLUSION: For the first time, these findings clarify the role of PIBF1 in regulating ATR/CHK1 signaling pathway and inhibiting the proliferation and migration of TNBC cell lines. These results demonstrate the oncogenic roles of PIBF1 and provide new insights into the function and the molecular mechanism of PIBF1 in malignant TNBC.

New target cells of the immunomodulatory effects of progesterone.

It is well known that the reproductive steroid hormones, particularly progesterone, in addition to its widely recognized effects on endometrial epithelial and stromal cells and spiral arteries, affect the activities of T cells and natural killer cells in the deciduas, thus inducing active immune tolerance against the fetal antigens. The immunomodulatory effects of progesterone on T cells, B cells and natural killer cells have been discussed extensively in the literature. The aim of the present review is to sum up and discuss the results from this and other laboratories of investigations on the effects of progesterone on dendritic cells and adult stem cells, which are some of the other cell populations present at the fetal-maternal interface and possibly are related to the immunoregulation during pregnancy. These cells have been shown to have a number of specific functions but their involvement in the entire process of regulation of the immune response in pregnancy is still under discussion. The present review focuses on facts showing that the progesterone is a kind of 'regulator of regulators' in the decidua, thus creating the most favourable conditions for the development of the semi-allogeneic fetus in successful pregnancy.

Regeneration and tolerance factor: a novel mediator of glioblastoma-associated immunosuppression.

Regeneration and tolerance factor (RTF) was originally identified in placenta where it is thought to be essential for fetal allograft survival. Here we report that RTF mRNA and protein are also expressed in human glioma cells in vitro and in vivo. Suppression of RTF expression by RNA interference promotes the lysis of glioma cells by natural killer (NK) and T cells in vitro. Moreover, RTF-depleted glioma cells are less tumorigenic than control cells in nude mice in vivo. Depletion of NK cells in these animals abolished this effect. RTF is thus a novel aberrantly expressed molecule which confers immune privilege to human malignant gliomas.

High Immune Expression of Progesterone-Induced Blocking Factor in Epithelial Ovarian Cancer.

BACKGROUND: Progesterone-induced blocking factor, which is released from maternal lymphocytes during pregnancy mediates the immune effect of progesterone. According to new reports, it is suggested that proliferating cells, such as human trophoblasts, mesenchymal stem cells, and malignant tumors, can excrete progesterone-induced blocking factor at high ratio to escape from maternal immunity. It is shown in recent studies that progesterone-induced blocking factor is overexpressed in many malignant tumors such as breast, cervical, lymphoma, and leukemia. There are no data about progesterone-induced blocking factor expression in ovarian cancer cells. Hence, it is aimed to determine the progesterone-induced blocking factor expression levels in epithelial ovarian cancer. METHODS: The study which was a retrospective cross-sectional study was conducted in a University Hospital. Twenty tissue specimens of patients with epithelial ovarian cancer and 20 tissue specimens of patients with healthy ovary were included in the study. Primary rabbit polyclonal anti- progesterone-induced blocking factor antibody was used to incubate the sections at a ratio of 1:300. RESULTS: When the tissue sections were compared based on immunostaining with progesterone-induced blocking factor, we detected high stromal progesterone-induced blocking factor expression in the epithelial ovarian cancer group as check against to the normal ovarian group ( P = .007). Similarly, we found high glandular progesterone-induced blocking factor expression in the epithelial ovarian cancer group as check against to the normal ovarian group ( P < .001). CONCLUSION: Proving the existence of progesterone-induced blocking factor expression in epithelial ovarian cancer cells may lead new visions or new studies for epithelial ovarian cancer immunotherapy. As a result, epithelial ovarian cancer cells have greater levels of expression of progesterone-induced blocking factor protein than normal ovarian tissue according to immunohistochemistry. Further research is needed to understand the clinical importance of this finding, to learn outcomes of high levels of progesterone-induced blocking factor, and to investigate its underlying mechanisms.

Steroid-sensitive mechanism of soluble immune response suppressor production in steroid-responsive nephrotic syndrome.

Soluble immune response suppressor (SIRS), a lymphokine that suppresses antibody production and delayed type hypersensitivity in vivo, has been detected in urine and serum from certain patients with nephrotic syndrome. In the present paper, the relationship between SIRS production and nephrotic syndrome is further characterized. A striking correlation was found between detection of SIRS and the presence of steroid-responsive nephrotic syndrome (SRNS). A potential mechanism of SIRS production in SRNS patients was identified, in that lymphocytes from patients produced SIRS without requiring activation by exogenous agents, and incubation of normal lymphocytes with serum from patients activated the cells to secrete SIRS in culture. Although SIRS disappears rapidly from urine or serum after initiation of corticosteroid therapy, hydrocortisone (10(-6)-10(-7) M) did not block secretion of SIRS by activated suppressor cells. It did, however, inhibit in vitro activation of lymphocytes to produce SIRS by concanavalin A, interferon, or SRNS patient serum. The association of suppressor cell activation with SRNS and the sensitivity of both to steroids suggest that the pathogeneses of albuminuria and SIRS production are related.

Schistosoma japonicum egg antigen-specific T cell lines in man. Induction of helper and suppressor T cell lines and clones in vitro in a patient with chronic schistosomiasis japonica.

T cell lines (TCLs) specific for Schistosoma japonicum egg antigen were established from a patient with chronic schistosomiasis japonica to investigate the regulatory mechanism of S.japonicum egg antigen-driven T cell responses in man. All five TCLs tested were CD2+, CD4+, CD8-, and were strongly proliferative only to S. japonicum egg antigen in the absence of exogenous IL-2. All but one TCL produced IL-2-like lymphokines in vitro, indicating their helper T cell functions. One TCL, SjE-3, failed to produce IL-2-like lymphokines. Moreover, this TCL suppressed the specific proliferation of autologous peripheral blood lymphocytes to S. japonicum egg antigen. This TCL produced a soluble suppressor factor(s). These functional diversities among established TCLs were also confirmed by cloned T cells. Our observations might suggest that the regulatory system through helper and suppressor T-T interactions somehow involved in T cell responses to the egg antigen in human chronic schistosomiasis japonica.

Suppressor lymphokine produced by rat T-cells in response to syngeneic mammary adenocarcinoma 13762A.

An antiproliferative suppressor lymphokine was produced from rat T-cells specifically in response to the poorly immunogenic syngeneic mammary adenocarcinoma 13762A. The tumor-induced suppressor lymphokine (TISL) was produced late in culture (peak production on Days 4 and 5) and showed strong but selective inhibitory activity on a variety of immune responses. The immune peritoneal exudate cell response to a highly immunogenic clone from the parental tumor (clone 18A) and the concanavalin A-stimulated response of nonimmune spleen cells were inhibited strongly by TISL. In contrast, the immune spleen cell response to 13762A and the lipopolysaccharide response of nonimmume spleen cells were unaffected. Preliminary molecular weight and physicochemical analysis of TISL indicated that the molecule was large (Mr greater than 350,000); partially sensitive to 75 degrees C treatment for 15 min and to pH 2.0 treatment; only partly degraded by the enzymes trypsin, chymotrypsin, and proteinase K; and completely destroyed by boiling. Although TISL was produced specifically in response to 13762A tumor, prior immunization in vivo was not necessary for the induction of the suppressor lymphokine. These results indicate that populations of rat lymphocytes contain naturally occurring TISL secreting cells, which can be activated specifically by tumor antigens such as those expressed by 13762A.

Induction of macrophage suppressor activity by fibrosarcoma-derived transforming growth factor-beta 1: contrasting effects on resting and activated macrophages.

Tumor-derived transforming growth factor-beta 1 (TGF-beta 1) suppresses several immune responses. Because tumor growth induces macrophage (m phi) suppressor activity, we determined whether murine fibrosarcoma-derived TGF-beta 1 contributed to m phi-mediated suppression of autoantigen- and alloantigen-stimulated T cell proliferation. The murine fibrosarcoma Meth-KDE cell line constitutively produced TGF-beta 1. Meth-KDE tumor-bearing host (TBH) syngeneic splenic m phi s suppressed autoantigen- and alloantigen-stimulated normal host (NH) CD4+ T cell proliferation. Pretreatment with Meth-KDE supernatants induced NH m phi s to suppress T cell proliferation as much as TBH m phi s. Anti-TGF-beta 1 antibody treatment reversed Meth-KDE-induced NH m phi-mediated suppression. Recombinant TGF-beta 1-induced m phi-mediated suppression was not blocked during inhibition of prostaglandin E2 (PGE2), nitric oxide (NO), or TGF-beta 1 production. However, Meth-KDE-induced m phi-mediated suppression was partly reduced when PGE2 production was inhibited. Pretreatment with tumor cell-derived TGF-beta 1, but not recombinant TGF-beta 1, increased activated m phi PGE2 production. These results show that additional tumor-derived molecules aid in TGF-beta 1-enhanced PGE2 production. Also, TGF-beta 1 alone up-regulates m phi synthesis of suppressor molecules that are different from PGE2, NO, and TGF-beta 1. Although TGF-beta 1 has direct suppressor activity on lymphocytes, these results show that release of tumor cell TGF-beta 1 also induces m phi suppressor activity.

Distribution of allergens and allergen-coding mRNAs in various tissues of white birch.

The distribution of allergenic proteins was investigated in various tissues of white birch, Betula verrucosa (pollen, leaves and male inflorescences containing immature pollen). In addition, callus and suspension culture cells were investigated for expression of IgE-binding proteins. Furthermore, RNA was extracted from all these tissues and subjected to in vitro translation in a cell-free wheat germ system. Bet v I, the major birch pollen allergen, could be extracted easily from pollen, and in low amounts from callus and leaves. No Bet v I could be extracted from immature male inflorescences. Minor allergens were expressed in high concentrations in pollen and in low concentrations in immature male inflorescences. No minor allergens could be detected in callus and leaves. In contrast to these observations, RNA from all the tissues as well as from callus could be translated in vitro into Bet v I as well as into minor allergens, in particular birch profilin (Bet v II), an important minor allergen. These data suggest that IgE-binding proteins of B. verrucosa, especially Bet v I, under certain circumstances can readily be synthesized in tissues other than pollen. This concept is corroborated by the recent observation that Bet v I reveals high homology with disease resistance response gene products from other plants, suggesting a similar function of Bet v I for the birch.

Enhancement of Fc epsilon RII/CD23 expression on U937 cells with opsonized zymosan: the requirement of a Fc gamma RI/CD64 mediated signal associated phagocytosis.

The kinetics of surface Fc epsilon RII/CD23 was tested on monocytic cell line U937 stimulated with opsonized zymosan. Zymosan opsonized with human serum enhanced not only the expression of surface Fc epsilon RII/CD23 but also Fc epsilon RII/CD23 mRNA detected by Northern blot and in situ hybridization techniques. This stimulation showed a marked synergism with IL-4 in the induction of Fc epsilon RII/CD23. Heat-inactivation of serum did not affect the inducibility of Fc epsilon RII/CD23 by opsonized zymosan, suggesting the involvement of serum substances other than complement. Zymosan treated with human gamma-globulin also induced Fc epsilon RII/CD23, indicating the possible involvement of Fc gamma receptors. The Fc epsilon RII/CD23 inducing effect of opsonized zymosan was partially blocked by pretreatment with heat-aggregated human gamma-globulin or an anti-Fc gamma RI monoclonal antibody but not by the anti-Fc gamma RII or Fc gamma RIII antibody. Our results showed the involvement of signals from Fc gamma receptor associated phagocytosis in the induction of Fc epsilon RII/CD23.

In vitro inhibition of tumor B cell growth by IgG-BF-producing Fc gamma RII+ T cell hybridoma and by immunoglobulin G-binding factors.

The growth-modulating effect on mouse hybridoma B cells of IgG-BF-producing Fc gamma RII+ mouse T cell hybridomas and of the IgG-BF isolated from the culture supernatants of these cells has been examined. Cocultures of IgG-secreting hybridoma B cells with IgG-BF-producing T hybridomas or with partially purified IgG-BF demonstrated a reproducible inhibition of the tumor B cell growth. The inhibition was due to a cytostatic and not to a cytotoxic effect. Hybridoma B cells cultured in liquid medium in the presence of soluble IgG-BF, or cocultured in semisolid agarose assays with IgG-BF-producing hybridoma T cells did not undergo immediate cytolysis but were prevented from proliferating. Thus, our data indicate that IgG-BF-producing Fc gamma RII+ T cells interfere with the proliferation of transformed B cells, possibly through soluble IgG-BF.

Murine soluble Fc gamma receptors/IgG-binding factors (IgG-BF): analysis of the relation to Fc gamma RII and production of milligram quantities of biologically active recombinant IgG-BF.

The production of soluble forms of low-affinity Fc gamma R by cells expressing recombinant or natural membrane Fc gamma RII, and the structural relationships between these soluble receptors and membrane Fc gamma RII are described. We show that 37-40 kD soluble Fc gamma RII, corresponding to the two N-terminal domains of Fc gamma RII and binding to IgG, are spontaneously produced in vitro by cleavage of membrane Fc gamma RII. Moreover, we describe methods to produce and purify to homogeneity large quantities of endotoxin-free recombinant IgG-binding factor (rIgG-BF) from the culture medium of a cell line transfected with a mutated Fc gamma RII cDNA. These methods include the use of bioreactors for culturing transfected fibroblasts and the purification of rIgG-BF by ion-exchange chromatography and hydrophobic-interaction chromatography. By using such procedures, about 2.4 mg of rIgG-BF were purified from 1 liter of culture medium of transfected fibroblasts. Like natural IgG-BF, the 95-99% pure rIgG-BF suppressed, in a dose-dependent manner, secondary in vitro IgG antibody responses to sheep red blood cells.

Isolation of rat/rat T cell hybrids using W/Fu C58(NT)D as fusion partner.

Functional rat/rat T cell hybrids were isolated for the first time by the fusion of spleen cells from rats tolerized to the hapten TNP to a HAT-sensitive rat thymoma (C58(NT)D). 11 fusions using different protocols were attempted to assess the optimal conditions for high hybridization frequency of the desired specificity. Interestingly, the cell density requirement of the non-transformed fusion partner took precedence over that of the C58 cell line, i.e., rat cells needed to be at high density after fusion, but others have reported that mouse cells prefer a much lower density even when the same line (C58) is used. Six fusions yielded hybridomas with between 3% and 70% of wells containing hybrids after three weeks of culture, depending on the protocol used. Phenotypically, all of the hybrids and clones tested expressed the W3/25 (rat CD4) antigen, but no OX-8 (rat CD8) or immunoglobulin molecules. A minority of hybrids were found to secrete factors able to suppress (a) proliferation, (b) antibody production, and (c) cells bearing IL-2 receptors, but none appeared to suppress the production of IL-2 itself. In contrast to non-transformed rat T cell lines, the T hybrids isolated were easy to grow to high densities, clone and freeze without the need to add exogenous antigen or lymphokines to the cultures at any stage.

Macrophage T cell interaction. Induction in vitro of a mediator with potent antisuppressor activity.

A simple in vitro method is described for the induction of a potent mediator that interferes with suppressor cell function. The mediator consists of three easily identifiable components, Ig, class II determinants and antigen, that form a unique complex similar to, or identical with, the complexes detected in vivo within 3-6 h after immunization. The formation of the antisuppressor mediator in vitro takes place in two steps: the first involves a macrophage-T cell interaction which generates an 'intermediate complex' containing antigen and class II determinants. In the second step the addition of immunochemically purified IgG from normal mouse serum to the macrophage-T cell supernate generates potent antisuppressor activity, which is assayed by the conversion of suppression to immunity. It is suggested that the IgG interacts with the 'intermediate complex' giving rise to the final complex identical to that found in vivo 6 h after immunization. No activity is detected when IgG is added to a supernate of antigen-fed macrophages in the absence of T cells. Furthermore, the T cell plays an additional important role in the formation of the final complexes since it restricts the source of the IgG that will generate the antisuppressor activity. In other words the antisuppressor function is detected only if the IgG matches the donor of the T cell in the Igh locus. The T cell involved in the formation of the complex is the Ly1+ subpopulation. This method should allow elucidation of the genetic, cellular and molecular mechanisms in the activation of this important T cell pathway.

Establishment of stable CD8+ suppressor T cell clones and the analysis of their suppressive function.

Stable CD8+ suppressor T cell (Ts) clones were established by a relatively simple method. Keyhole limpet hemocyanin (KLH)-primed spleen cells from C3H mice were depleted of B cells and CD4+ T cells by panning and cytotoxic treatment, and the resulting CD8+ T cells were periodically stimulated with antigen and irradiated syngeneic spleen cells followed by manifestation in interleukin-2 (IL-2) containing medium. T cell clones with a definite suppressor function were established by limiting dilution. They were defined as classical effector type Ts of CD8+ phenotype as they had constant and definite suppressor functions in antigen-induced T cell proliferation and specific antibody response against T cell-dependent antigens without detectable cytotoxic activity against both antigen presenting cells (APC) and helper T cells (Th). They showed no helper activity for B cells and produced no detectable helper type lymphokines such as IL-2 and IL-4. CD8+ Ts clones were able to inhibit the antigen-induced IL-2 production of normal and cloned T cells. Their suppressive activity was antigen-nonspecific and major histocompatibility complex-unrestricted. CD8+ Ts clones were also able to suppress the proliferative response of Th clones induced by immobilized anti-T cell receptor (TcR) and anti-CD3 mAbs but not the response induced by concanavalin A (ConA) and IL-2. All the CD8+ T cell clones established independently utilized the TcR V beta 8 gene. Syngeneic antigen presenting cells could induce proliferation of these CD8+ clones, which was blocked by anti-CD8 and anti-I-Ak monoclonal antibody (mAb) but not by anti-class I mAbs. The stimulation of CD8+ Ts clones with immobilized anti-CD3 resulted in the release of a suppressor factor(s) that potently inhibited the antigen-induced proliferation of CD4+ Th clones and the in vitro secondary antibody formation.

A comparative investigation of CC chemokines and SIV suppressor factors generated by CD8+ and CD4+ T cells and CD14+ monocytes.

The capacity of CD8+ and CD4+ T cells and CD14+ monocytes to generate the CC chemokines, RANTES, MIP-1alpha and MIP-1beta, and SIV suppressor factors were studied using cells separated from PBMC of macaques immunized with the 70-kDa heat shock protein (HSP70). Unimmunized macaques showed low levels of the three CC chemokines and SIV-SF, and they showed little variation between PBMC and the two subsets of T cells stimulated with PHA. Immunization with HSP70 elicited an increase in the in vitro concentration of each of the three CC chemokines and SF. This was found with PBMC, CD4+ and CD8+ T cells and to a lesser extent with monocytes, when conventionally separated enriched cell subsets were examined from the same PBMC. However, the concentrations of the three CC chemokines derived from highly purified cell-sorted populations (>95%) were greatly increased, as compared with the enriched cell subsets. The concentration of each of the three chemokines was highest for CD8+ T cells, decreased with CD4+ T cells and was lowest with the CD14+ monocytes, but the latter were not stimulated. Neutralization assays with antibodies to the three CC chemokines showed that the antiviral activity generated by the four populations of cells could be largely accounted for by the three CC chemokines. The results of this comparative study suggests that CD8+ as well as CD4+ T cells and CD14+ monocytes generate the three CC chemokines and SIV-SF when stimulated with a mitogen, and that the baseline innate level can be upregulated by adaptive immune responses to a specific antigen.

Glucocorticoid involvement in suppression of NK activity following surgery in rats.

We studied plasma factors mediating suppression of NK activity (NKA) following surgery. Plasma from operated rats suppressed NKA of splenocytes, leukocytes, and purified natural killer (NK) cells, and charcoal stripping nullified suppression. The glucocorticoid antagonist mifepristone prevented suppression, whereas blockers of reactive oxygen metabolites, opioids, catecholamines, prostaglandin-E2, and histamine did not. NKA dropped as corticosterone levels peaked postoperatively, and administration of relevant doses of corticosterone suppressed NKA. Inhibition of glucocorticoid synthesis prevented plasma from suppressing NKA but merely attenuated NKA suppression in operated rats. Thus, postoperative concentrations of corticosterone can directly suppress NKA but additional factors probably act in vivo.

Correlation between PGE2 production and suppressor activity of alveolar macrophages from patients with interstitial lung diseases.

The suppressive activity of alveolar macrophages (AM) obtained from bronchoalveolar lavage (BAL), on PHA stimulation of autologous peripheral blood lymphocytes (APL) was evaluated. The effect on lymphocyte stimulation was evaluated by coculturing the AM and APL cells at a ratio of 1:1. PGE2 released by AM during the culture period was measured by a radioimmune assay. The patients included in the study were 11 cases with interstitial lung disease (ILD), 8 cases of lung cancer (CA), and 5 controls (CO). Addition of AM of patients from the CA group resulted in slight suppression of lymphocyte stimulation in 4 cases, slight enhancement in 3 cases and no effect in one case. AM from the CO group induced slight suppression in 4 out of 5 cases. AM from all 11 ILD cases exerted a significant high suppressive activity (65.6% +/- 18.2 - P less than 0.001 by comparison with the CO and CA groups). In ILD cases, a dichotomous pattern was found in regard to relation between high suppressive activity of AM and release of PGE2: in idiopathic pulmonary fibrosis (IPF) patients, high suppressive activity of AM (70.4% +/- 15.4) correlated well with elevated secretion of PGE2: 3.58 +/- 0.26 ng/ml/10(5) cells (P less than 0.02 compared to CO). AM from sarcoidosis patients suppressed PHA stimulation by 61.6% +/- 19.3 but secreted only 0.357 +/- 0.26 ng/ml/10(5) cells of PGE2 (P less than 0.02 compared with the idiopathic pulmonary fibrosis group). Therefore, it seems that other factors, in addition to PGE2, might be involved in the suppressive activity of AM from interstitial lung diseases.

Characteristics of a human liver allograft--derived T-cell line that exhibits suppressor activity.

In an attempt to identify predominant cell populations that may mediate liver allograft dysfunction, the phenotypic and functional characteristics of lymphoid cells propagated from needle biopsy specimens of rejecting liver transplants were examined. In one case, a T-cell line of host phenotype propagated from a liver allograft biopsy demonstrated significant in vitro suppressor activity. This T-cell line (designated JB) was maintained for almost one year in culture with medium containing human recombinant interleukin 2 and with weekly stimulation by an Epstein-Barr virus-transformed B-cell line derived from the liver donor. Repeated analyses demonstrated that the JB line was phenotypically stable and predominantly CD3+ (86-93%), CD4+ (88-96%), DR+ (96%), Leu8-, CD45R-, CD16-, with a minor CD8+ cell population (less than 5%). The JB line demonstrated proliferative responsiveness upon coculture with cells expressing disparate donor HLA antigens but no in vitro cytotoxic activity. However, JB cells significantly (greater than 90%) suppressed mixed lymphocyte reaction or phytohemagglutinin stimulation of nonautologous peripheral blood lymphocytes. Supernatants of JB cells that had been cultured alone or with irradiated (6000 rads) Epstein-Barr virus-transformed donor B cells mimicked the suppressive activity of the JB cell line, either upon addition in vitro or by transient (4 hr) pretreatment of responder cells at 20 degrees C. JB cell supernatants were nontoxic and free of tumor necrosis factor activity, and their suppressive activity was dose-dependent, nondialyzable (greater than 100 kDa), not overcome by exogenous interleukin 1 or interleukin 2, and heat-resistant up to 56 degrees C. However, the suppressive activity of JB supernatants could be diminished or abrogated by treatment with high temperature (80-100 degrees C), reducing agents, trypsin, or absorption by peripheral blood lymphocytes at room temperature. The suppressive activity of JB cells and supernatants was not alloantigen-specific or major histocompatibility complex-restricted, did not shift mixed lymphocyte reaction kinetics, and was capable of inhibiting in vitro stimulation of peripheral blood lymphocytes in mixed lymphocyte reaction only when presented early in the culture. These findings provide the first evidence for a primary human allograft-derived T-cell line with suppressor-effective function.

Regeneration and tolerance factor is expressed during T-lymphocyte activation and plays a role in apoptosis.

Regeneration and tolerance factor (RTF) is a protein cloned from the thymus and expressed on B lymphocytes in normal pregnancy, B lymphocytic leukemia lines, and T and B lymphocytes in individuals with HIV infection. Findings, using the Jurkat T-cell model, revealed that RTF is upregulated after activation and anti-RTF antibody-induced apoptosis. In this article anti-RTF antibody-induced apoptosis of both unstimulated and activated T lymphocytes. RTF expression was examined in human PBMC or purified T lymphocytes after their in vitro activation. Kinetic studies indicated maximal RTF cell surface expression on activated T lymphocytes occurred between expression of the early activation antigen CD69 and the IL-2alpha receptor (CD25) by multiparameter flow cytometry. RTF receptor expression correlated with Fas (CD95) and CD25 receptor expression (r2 = 0.6 and 0.5, respectively). RTF surface expression was dependent on the stimuli used to activate T lymphocytes. T lymphocytes obtained maximal RTF expression when activated through the TCR signal complex using anti-CD3epsilon antibody alone when compared with T lymphocytes activated with costimulation provided by anti-CD28 antibody alone or with anti-CD28 and anti-CD3epsilon antibody. RTF is expressed under conditions of both activation and anergy. The RTFs increased concentration on the surface of anergic T cells may protect these cells from apoptosis because increased RTF concentrations inhibited anti-RTF induced apoptosis. These data further characterize the expression of RTF on activated T lymphocytes and the role of anti-RTF antibody in T-lymphocyte apoptosis.