Coordinate expression and proliferative role of HOXB genes in activated adult T lymphocytes

1994 ◽  
Vol 14 (7) ◽  
pp. 4872-4877
Author(s):  
A Carè ◽  
U Testa ◽  
A Bassani ◽  
E Tritarelli ◽  
E Montesoro ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
Retinoic Acid ◽  
T Cell ◽  
T Lymphocytes ◽  
T Cell Activation ◽  
Cell Activation ◽  
Rnase Protection ◽  
Activated T Lymphocytes

We investigated the expression of HOXB cluster genes in purified phytohemagglutinin (PHA)-activated T lymphocytes from normal adult peripheral blood by reverse transcription PCR and RNase protection. These genes are not expressed in quiescent T cells, except for barely detectable B1 RNA. After the PHA stimulus, HOXB gene activation initiates coordinately as a rapid induction wave in the 3'-->5' cluster direction (i.e., from HOXB1 through B9 genes). Thus, (i) expression of the foremost 3'-located B1 and B2 genes peaks 10 min after PHA addition and then rapidly declines, (ii) activation of B3, B4, and B5 begins 10 min after PHA addition and peaks at later times (i.e., at 120 min for B5), (iii) B6, B7, and B9 are expressed at a low level starting at later times (45 to 60 min), and (iv) B8 remains silent. Treatment of PHA-activated T lymphocytes with antisense oligonucleotides to B2 or B4 mRNA causes a drastic inhibition of T-cell proliferation and a decreased expression of T-cell activation markers (i.e., interleukin 2 and transferrin receptors). Similarly, treatment of CEM-CCRF, Peer, and SEZ627 T acute lymphocytic leukemia cell lines with anti-B4 oligomer markedly inhibits cell proliferation. Finally, T cells stimulated by a low dosage of PHA in the presence of 1 microM retinoic acid show a marked increase of both HOXB expression, particularly B2, and cell proliferation. These studies provide novel evidence on the role of HOX genes in adult cell proliferation. (i) Coordinate, early activation of HOXB genes from the 3'-->5' cluster side apparently underlies T-cell activation. (ii) The expression pattern in adult PHA-activated T cells is strikingly similar to that observed in retinoic acid-induced teratocarcinoma cells (A. Simeone, D. Acampora, L. Arcioni, P. W. Andres, E. Boncinelli, and F. Mavilio, Nature (London) 346:763-766, 1990), thus suggesting that molecular mechanisms underlying HOX gene expression in the earliest stages of development may also operate in activated adult T lymphocytes.

scholarly journals Coordinate expression and proliferative role of HOXB genes in activated adult T lymphocytes.

1994 ◽  
Vol 14 (7) ◽  
pp. 4872-4877 ◽  
Author(s):  
A Carè ◽  
U Testa ◽  
A Bassani ◽  
E Tritarelli ◽  
E Montesoro ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
Retinoic Acid ◽  
T Cell ◽  
T Lymphocytes ◽  
T Cell Activation ◽  
Cell Activation ◽  
Rnase Protection ◽  
Activated T Lymphocytes

We investigated the expression of HOXB cluster genes in purified phytohemagglutinin (PHA)-activated T lymphocytes from normal adult peripheral blood by reverse transcription PCR and RNase protection. These genes are not expressed in quiescent T cells, except for barely detectable B1 RNA. After the PHA stimulus, HOXB gene activation initiates coordinately as a rapid induction wave in the 3'-->5' cluster direction (i.e., from HOXB1 through B9 genes). Thus, (i) expression of the foremost 3'-located B1 and B2 genes peaks 10 min after PHA addition and then rapidly declines, (ii) activation of B3, B4, and B5 begins 10 min after PHA addition and peaks at later times (i.e., at 120 min for B5), (iii) B6, B7, and B9 are expressed at a low level starting at later times (45 to 60 min), and (iv) B8 remains silent. Treatment of PHA-activated T lymphocytes with antisense oligonucleotides to B2 or B4 mRNA causes a drastic inhibition of T-cell proliferation and a decreased expression of T-cell activation markers (i.e., interleukin 2 and transferrin receptors). Similarly, treatment of CEM-CCRF, Peer, and SEZ627 T acute lymphocytic leukemia cell lines with anti-B4 oligomer markedly inhibits cell proliferation. Finally, T cells stimulated by a low dosage of PHA in the presence of 1 microM retinoic acid show a marked increase of both HOXB expression, particularly B2, and cell proliferation. These studies provide novel evidence on the role of HOX genes in adult cell proliferation. (i) Coordinate, early activation of HOXB genes from the 3'-->5' cluster side apparently underlies T-cell activation. (ii) The expression pattern in adult PHA-activated T cells is strikingly similar to that observed in retinoic acid-induced teratocarcinoma cells (A. Simeone, D. Acampora, L. Arcioni, P. W. Andres, E. Boncinelli, and F. Mavilio, Nature (London) 346:763-766, 1990), thus suggesting that molecular mechanisms underlying HOX gene expression in the earliest stages of development may also operate in activated adult T lymphocytes.

CD11b+gr-1+ myeloid Derived Suppressor Cells (MDSC) In Normal Bone Marrow Suppress T Cell Proliferation and Enhance T-Regulatory Function Via a IL10-, IL4- and IDO-Independent Mechanism

Blood ◽  
2010 ◽  
Vol 116 (21) ◽  
pp. 4801-4801 ◽  
Author(s):  
Parvin Forghani ◽  
Wayne Harris ◽  
jian-Ming Li ◽  
M.R. Khorramizadeh ◽  
Edmund Waller
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
Regulatory Function ◽  
T Cell Proliferation ◽  
Suppressive Activity ◽  
Ifn Γ

Abstract Abstract 4801 MDSC have been described as an important negative regulators of autologous anti-cancer immune responses. Considering the important role of MDSC in immune regulation in allogenic stem cell and organ transplantation, we undertook an investigation of the mechanism(s) by which MDSC inhibit T–cell activation and proliferation, and tested the hypothesis that local cytokine secretion or IDO activity is required for suppression of T-cell proliferation. Two separate populations CD11bhiGr-1hi and CD11bhi Gr-1int were isolated by high-speed FACS from lineage- BM antigen presenting cells (C57 & BALB/c mice). Both MDSC subsets had potent capacity for in–vitro suppression of CD4+ and CD8+ T cells proliferation in response to anti-CD3/anti-CD28 beads and Con A. A ratio of 0.5/1 MDSC: T-cells were sufficient to inhibit >66% control levels of T-cell proliferation. MDSC isolated from transgenic mice that had been “knocked-out” for IFN-γ and IDO had equivalent suppressive activity as MDSC from wild-type donors. Addition of saturating concentrations of anti IL-10 and IL-4 MAb, or in combination with anti- IFN-γ MAb did not abrogate MDSC-suppressive activity. Ex-vivo culture of MDSC with mitogen-activated T-cells generated two—fold more Fox-p3 T-reg compared with cultures of T cell plus mitogen. Data will be presented regarding the novel role of MDSC involving in the homeostasis regulation of normal T-cell activation and proliferation in non-tumor-bearing mice. Disclosures: No relevant conflicts of interest to declare.

An emerging player in the adaptive immune response: microRNA-146a is a modulator of IL-2 expression and activation-induced cell death in T lymphocytes

Blood ◽  
2010 ◽  
Vol 115 (2) ◽  
pp. 265-273 ◽  
Author(s):  
Graziella Curtale ◽  
Franca Citarella ◽  
Claudia Carissimi ◽  
Marina Goldoni ◽  
Nicoletta Carucci ◽  
...  
Keyword(s):  
Immune Response ◽  
T Cells ◽  
Cell Death ◽  
T Cell ◽  
T Lymphocytes ◽  
T Cell Activation ◽  
Cell Activation ◽  
Interleukin 2 ◽  
Activation Induced Cell Death

Abstract Activation of the T cell–mediated immune response has been associated with changes in the expression of specific microRNAs (miRNAs). However, the role of miRNAs in the development of an effective immune response is just beginning to be explored. This study focuses on the functional role of miR-146a in T lymphocyte–mediated immune response and provides interesting clues on the transcriptional regulation of miR-146a during T-cell activation. We show that miR-146a is low in human naive T cells and is abundantly expressed in human memory T cells; consistently, miR-146a is induced in human primary T lymphocytes upon T-cell receptor (TCR) stimulation. Moreover, we identified NF-kB and c-ETS binding sites as required for the induction of miR-146a transcription upon TCR engagement. Our results demonstrate that several signaling pathways, other than inflammation, are influenced by miR-146a. In particular, we provide experimental evidence that miR-146a modulates activation-induced cell death (AICD), acting as an antiapoptotic factor, and that Fas-associated death domain (FADD) is a target of miR-146a. Furthermore, miR-146a enforced expression impairs both activator protein 1 (AP-1) activity and interleukin-2 (IL-2) production induced by TCR engagement, thus suggesting a role of this miRNA in the modulation of adaptive immunity.

scholarly journals The role of extracellular vesicles and PD-L1 in glioblastoma-mediated immunosuppressive monocyte induction

2020 ◽  
Vol 22 (7) ◽  
pp. 967-978 ◽  
Author(s):  
Benjamin T Himes ◽  
Timothy E Peterson ◽  
Tristan de Mooij ◽  
Luz M Cumba Garcia ◽  
Mi-Yeon Jung ◽  
...  
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
T Cell ◽  
Extracellular Vesicles ◽  
T Cell Activation ◽  
Cell Activation ◽  
T Cell Proliferation ◽  
Cell Inhibition

Abstract Background Immunosuppression in glioblastoma (GBM) is an obstacle to effective immunotherapy. GBM-derived immunosuppressive monocytes are central to this. Programmed cell death ligand 1 (PD-L1) is an immune checkpoint molecule, expressed by GBM cells and GBM extracellular vesicles (EVs). We sought to determine the role of EV-associated PD-L1 in the formation of immunosuppressive monocytes. Methods Monocytes collected from healthy donors were conditioned with GBM-derived EVs to induce the formation of immunosuppressive monocytes, which were quantified via flow cytometry. Donor-matched T cells were subsequently co-cultured with EV-conditioned monocytes in order to assess effects on T-cell proliferation. PD-L1 constitutive overexpression or short hairpin RNA–mediated knockdown was used to determined the role of altered PD-L1 expression. Results GBM EVs interact with both T cells and monocytes but do not directly inhibit T-cell activation. However, GBM EVs induce immunosuppressive monocytes, including myeloid-derived suppressor cells (MDSCs) and nonclassical monocytes (NCMs). MDSCs and NCMs inhibit T-cell proliferation in vitro and are found within GBM in situ. EV PD-L1 expression induces NCMs but not MDSCs, and does not affect EV-conditioned monocytes T-cell inhibition. Conclusion These findings indicate that GBM EV-mediated immunosuppression occurs through induction of immunosuppressive monocytes rather than direct T-cell inhibition and that, while PD-L1 expression is important for the induction of specific immunosuppressive monocyte populations, immunosuppressive signaling mechanisms through EVs are complex and not limited to PD-L1.

Bortezomib Induces Selective Depletion of Activated T Lymphocytes and Modifies the Cytokine’s Production Pattern.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 615-615
Author(s):  
Belen Blanco ◽  
Jose A. Perez-Simon ◽  
Luis I. Sanchez-Abarca ◽  
Xonia Carvajal-Vergara ◽  
Juan Mateos ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Lymphocytes ◽  
T Cell Activation ◽  
Cell Activation ◽  
Activated T Cells ◽  
Alloreactive T Cells ◽  
Lymphocyte Cultures ◽  
Activated T Lymphocytes ◽  
Mixed Lymphocyte Cultures

Abstract The NF-kB family has emerged as a key transducer of inflammatory signals involved in dendritic cell maturation and T lymphocyte activation. Accordingly, the diverse signaling pathways downstream of TCR/CD3 converge on several transcription factors including NFAT, AP-1 and NF-kB. We explored the ability of the proteosome inhibitor bortezomib, which prevents Nuclear Factor kB (NF-kB) activation, to block T-cell activation, proliferation and survival within alloreactive as compared to resting T-cells. For this purpose, T-cells were stimulated with PHA, aCD3/aCD28, allogeneic dendritic cells (APC) or through mixed lymphocyte cultures. NF-kB expression increased in activated T-lymphocytes as compared to resting T-cells. Interestingly, the higher the NF-kB expression, the more intense the proliferative blockade induced by bortezomib. This effect on proliferation was due to a selective induction of apoptosis among activated T-cells. Thus, after mixed lymphocyte reaction (MLR) cultures, alloreactive T-cells were 2 logs more sensitive to bortezomib-induced apoptosis than the resting T-cell counterpart as assessed by annexin / 7AAD staining. This effect of bortezomib was partially blocked by adding the caspase inhibitor Z-VAD to the culture. The addition of bortezomib not only decreased the proliferation and viability of activated T-lymphocytes but also the levels of IFN-g and IL-2, which were significantly decreased among activated T-cells cultured with bortezomib at doses ranging from 10 to 100 nM. Secondary mixed lymphocyte cultures demonstrated a selective loss of alloreactive T-cells while activation and proliferation against third party donor was partially preserved. In conclusion, at concentrations reached in the clinical setting, bortezomib induces selective apoptosis and decreases Th1 response among alloreactive T-lymphocytes while it barely affects unstimulated T-cells. These results establish the basis for the clinical use of bortezomib in the management of GVHD

Bortezomib induces selective depletion of alloreactive T lymphocytes and decreases the production of Th1 cytokines

Blood ◽  
2006 ◽  
Vol 107 (9) ◽  
pp. 3575-3583 ◽  
Author(s):  
Belén Blanco ◽  
José A. Pérez-Simón ◽  
Luis I. Sánchez-Abarca ◽  
Xonia Carvajal-Vergara ◽  
Juan Mateos ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Lymphocytes ◽  
T Cell Activation ◽  
Cell Activation ◽  
Nuclear Factor Κb ◽  
Third Party ◽  
Activated T Cells ◽  
Activated T Lymphocytes ◽  
Induced Apoptosis

We explored the ability of the proteasome inhibitor bortezomib, which prevents nuclear factor κB (NF-κB) activation, to block T-cell activation, proliferation, and survival within alloreactive compared with resting T cells. For this purpose, T cells were stimulated with PHA, αCD3/αCD28, or allogeneic dendritic cells or through mixed lymphocyte cultures. NF-κB expression increased in activated T lymphocytes compared with resting T cells. Of interest, the higher the NF-κB expression, the more intense the proliferative blockade induced by bortezomib. Moreover, after mixed lymphocyte reaction (MLR) cultures, alloreactive T cells were 2 logs more sensitive to bortezomib-induced apoptosis than the resting T-cell counterpart. This effect was due to a selective induction of apoptosis among activated T cells that was related to caspase activation and cleavage of the antiapoptotic bcl-2 protein and was partially abolished by the addition of the pancaspase inhibitor Z-VAD-FMK. In addition, after secondary MLR, the number of activated T cells was significantly reduced among T lymphocytes previously cultured with bortezomib when cells from the same donor were used as stimulating cells. By contrast, when third-party donor cells were used as stimulating cells, no significant differences were observed between T lymphocytes previously exposed or not to the drug, indicating a highly specific depletion of T lymphocytes alloreactive against primary donor antigens. The addition of bortezomib decreased not only the proliferation and viability of activated T lymphocytes but also the levels of IFNγ and IL-2, which were significantly decreased among activated T cells cultured with bortezomib at doses ranging from 10 to 100 nM. In conclusion, at concentrations reached in the clinical setting, bortezomib induces selective apoptosis and decreases Th1 response among alloreactive T lymphocytes while it barely affects unstimulated T cells. These results establish the basis for the clinical use of bortezomib in the management of graft-versus-host disease (GVHD).

scholarly journals Ebola Virus Binding to Tim-1 on T Lymphocytes Induces a Cytokine Storm

mBio ◽  
2017 ◽  
Vol 8 (5) ◽  
Author(s):  
Patrick Younan ◽  
Mathieu Iampietro ◽  
Andrew Nishida ◽  
Palaniappan Ramanathan ◽  
Rodrigo I. Santos ◽  
...  
Keyword(s):  
T Cells ◽  
T Cell ◽  
T Lymphocytes ◽  
T Cell Activation ◽  
Cell Activation ◽  
Ebola Virus ◽  
Dependent Manner ◽  
Cytokine Storm

ABSTRACT Ebola virus (EBOV) disease (EVD) results from an exacerbated immunological response that is highlighted by a burst in the production of inflammatory mediators known as a “cytokine storm.” Previous reports have suggested that nonspecific activation of T lymphocytes may play a central role in this phenomenon. T-cell immunoglobulin and mucin domain-containing protein 1 (Tim-1) has recently been shown to interact with virion-associated phosphatidylserine to promote infection. Here, we demonstrate the central role of Tim-1 in EBOV pathogenesis, as Tim-1−/− mice exhibited increased survival rates and reduced disease severity; surprisingly, only a limited decrease in viremia was detected. Tim-1−/− mice exhibited a modified inflammatory response as evidenced by changes in serum cytokines and activation of T helper subsets. A series of in vitro assays based on the Tim-1 expression profile on T cells demonstrated that despite the apparent absence of detectable viral replication in T lymphocytes, EBOV directly binds to isolated T lymphocytes in a phosphatidylserine–Tim-1-dependent manner. Exposure to EBOV resulted in the rapid development of a CD4Hi CD3Low population, non-antigen-specific activation, and cytokine production. Transcriptome and Western blot analysis of EBOV-stimulated CD4+ T cells confirmed the induction of the Tim-1 signaling pathway. Furthermore, comparative analysis of transcriptome data and cytokine/chemokine analysis of supernatants highlight the similarities associated with EBOV-stimulated T cells and the onset of a cytokine storm. Flow cytometry revealed virtually exclusive binding and activation of central memory CD4+ T cells. These findings provide evidence for the role of Tim-1 in the induction of a cytokine storm phenomenon and the pathogenesis of EVD. IMPORTANCE Ebola virus infection is characterized by a massive release of inflammatory mediators, which has come to be known as a cytokine storm. The severity of the cytokine storm is consistently linked with fatal disease outcome. Previous findings have demonstrated that specific T-cell subsets are key contributors to the onset of a cytokine storm. In this study, we investigated the role of Tim-1, a T-cell-receptor-independent trigger of T-cell activation. We first demonstrated that Tim-1-knockout (KO) mice survive lethal Ebola virus challenge. We then used a series of in vitro assays to demonstrate that Ebola virus directly binds primary T cells in a Tim-1–phosphatidylserine-dependent manner. We noted that binding induces a cytokine storm-like phenomenon and that blocking Tim-1–phosphatidylserine interactions reduces viral binding, T-cell activation, and cytokine production. These findings highlight a previously unknown role of Tim-1 in the development of a cytokine storm and “immune paralysis.” IMPORTANCE Ebola virus infection is characterized by a massive release of inflammatory mediators, which has come to be known as a cytokine storm. The severity of the cytokine storm is consistently linked with fatal disease outcome. Previous findings have demonstrated that specific T-cell subsets are key contributors to the onset of a cytokine storm. In this study, we investigated the role of Tim-1, a T-cell-receptor-independent trigger of T-cell activation. We first demonstrated that Tim-1-knockout (KO) mice survive lethal Ebola virus challenge. We then used a series of in vitro assays to demonstrate that Ebola virus directly binds primary T cells in a Tim-1–phosphatidylserine-dependent manner. We noted that binding induces a cytokine storm-like phenomenon and that blocking Tim-1–phosphatidylserine interactions reduces viral binding, T-cell activation, and cytokine production. These findings highlight a previously unknown role of Tim-1 in the development of a cytokine storm and “immune paralysis.”

The Inhibitory Role of Lactacystin and β-Lactacystin on T-cell Activation and Proliferation

2004 ◽  
Vol 36 (2) ◽  
pp. 123-127 ◽  
Author(s):  
Peng-Hong Song ◽  
Hai-Yang Xie ◽  
Shu-Sen Zheng ◽  
Jian Wu
Keyword(s):  
Flow Cytometry ◽  
T Cells ◽  
T Cell ◽  
T Lymphocytes ◽  
T Cell Activation ◽  
Cell Activation ◽  
Proteasome Inhibitors ◽  
Rt Pcr ◽  
Down Regulation

Abstract To evaluate the effects of proteasome inhibitors lactacystin (LAC) and β-lactacystin (β-LAC) on the proliferation and activation of T lymphocytes, flow cytometry was used to analyze the proliferation and the expression of CD69, CD25 and CD3 of T lymphocytes activated by PHA. Furthermore, the expressions of PA28 and IL-2 mRNA were assayed by competitive RT-PCR. The results indicated that: (1) LAC and β-LAC significantly decreased the incorporation of BrdU and inhibited T lymphocytes proliferation in T lymphocytes activated by PHA; (2) although LAC and β-LAC did not affect the expression of CD69 at any time, they significantly inhibited the expression of CD25 (48 h, 72 h, P<0.05); (3) in comparison with control, LAC and β-LAC significantly down-regulated the expression of PA28 and IL-2 mRNA (48 h, 72 h, P<0.05). LAC and β-LAC significantly inhibited the proliferation and activation of T cells. Mechanisms involved are inhibition of CD25 and down-regulation of PA28 and IL-2 mRNA expressions.

scholarly journals Costimulation by B7 Modulates Specificity of Cytotoxic T Lymphocytes: A Missing Link That Explains Some Bystander T Cell Activation

1997 ◽  
Vol 186 (10) ◽  
pp. 1787-1791 ◽  
Author(s):  
Pan Zheng ◽  
Yang Liu
Keyword(s):  
Cell Proliferation ◽  
T Cells ◽  
Influenza Virus ◽  
T Cell ◽  
T Cell Activation ◽  
Cell Activation ◽  
T Cell Proliferation ◽  
Target Cells ◽  
Cell Proliferation And Differentiation ◽  
Proliferation And Differentiation

It has been proposed that some bystander T cell activation may in fact be due to T cell antigen receptor (TCR) cross-reactivity that is too low to be detected by the effector cytotoxic T lymphocyte (CTL). However, this hypothesis is not supported by direct evidence since no TCR ligand is known to induce T cell proliferation and differentiation without being recognized by the effector CTL. Here we report that transgenic T cells expressing a T cell receptor to influenza virus A/NT/68 nucleoprotein (NP) 366-374:Db complexes clonally expand and become effector CTLs in response to homologous peptides from either A/PR8/34 (H1N1), A/AA/60 (H2N2), or A/NT/68 (H3N2). However, the effector T cells induced by each of the three peptides kill target cells pulsed with NP peptides from the H3N2 and H2N2 viruses, but not from the H1N1 virus. Thus, NP366–374 from influenza virus H1N1 is the first TCR ligand that can induce T cell proliferation and differentiation without being recognized by CTLs. Since induction of T cell proliferation was mediated by antigen-presenting cells that express costimulatory molecules such as B7, we investigated if cytolysis of H1N1 NP peptide–pulsed targets can be restored by expressing B7-1 on the target cells. Our results revealed that this is the case. These data demonstrated that costimulatory molecule B7 modulates antigen specificity of CTLs, and provides a missing link that explains some of the bystander T cell activation.

scholarly journals Immune function of the blood-brain barrier: incomplete presentation of protein (auto-)antigens by rat brain microvascular endothelium in vitro.

1990 ◽  
Vol 110 (5) ◽  
pp. 1757-1766 ◽  
Author(s):  
W Risau ◽  
B Engelhardt ◽  
H Wekerle
Keyword(s):  
T Cells ◽  
Endothelial Cells ◽  
T Cell ◽  
T Lymphocytes ◽  
Rat Brain ◽  
Blood Brain Barrier ◽  
T Cell Activation ◽  
Cell Activation ◽  
Ifn Gamma

The endothelial blood-brain barrier (BBB) has a critical role in controlling lymphocyte traffic into the central nervous system (CNS), both in physiological immunosurveillance, and in its pathological aberrations. The intercellular signals that possibly could induce lymphocytes to cross the BBB include immunogenic presentation of protein (auto-)antigens by BBB endothelia to circulating T lymphocytes. This concept has raised much, though controversial, attention. We approached this problem by analyzing in vitro immunospecific interactions between clonal rat T lymphocyte lines with syngeneic, stringently purified endothelial monolayer cultures from adult brain micro-vessels. The rat brain endothelia (RBE) were established from rat brain capillaries using double collagenase digestion, density gradient fractionation and selective cytolysis of contaminating pericytes by anti-Thy 1.1 antibodies and complement. Incubation with interferon-gamma in most of the brain-derived endothelial cells induced Ia-antigens in the cytoplasm and on the cell surface in some of the cells. Before the treatment, the cells were completely Ia-negative. Pericytes were unresponsive to IFN-gamma treatment. When confronted with syngeneic T cell lines specific for protein (auto-)antigens (e.g., ovalbumin and myelin basic protein, MBP), RBE were completely unable to induce antigen-specific proliferation of syngeneic T lymphocytes irrespective of pretreatment with IFN-gamma and of cell density. RBE were inert towards the T cells, and did not suppress T cell activation induced by other "professional" antigen presenting cells (APC) such as thymus-derived dendritic cells or macrophages. IFN-gamma-treated RBE were, however, susceptible to immunospecific T cell killing. They were lysed by MBP-specific T cells in the presence of the specific antigen or Con A. Antigen dependent lysis was restricted by the appropriate (MHC) class II product. We conclude that the interaction of brain endothelial cells with encephalitogenic T lymphocytes may involve recognition of antigen in the molecular context of relevant MHC products, but that this interaction per se is insufficient to initiate the full T cell activation program.

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