The TNF-like ligands APRIL and BLyS are close relatives and share the capacity to bind the receptors TACI and BCMA. BLyS has been shown to play an important role in B cell homeostasis and autoimmunity, but the biological role of APRIL remains less well defined. Analysis of T cells revealed an activation-dependent increase in APRIL mRNA expression. We therefore generated mice expressing APRIL as a transgene in T cells. These mice appeared normal and showed no signs of B cell hyperplasia. Transgenic T cells revealed a greatly enhanced survival in vitro as well as enhanced survival of staphylococcal enterotoxin B–reactive CD4+ T cells in vivo, which both directly correlate with elevated Bcl-2 levels. Analysis of humoral responses to T cell–dependent antigens in the transgenic mice indicated that APRIL affects only IgM but not IgG responses. In contrast, T cell–independent type 2 (TI-2) humoral response was enhanced in APRIL transgenic mice. As TACI was previously reported to be indispensable for TI-2 antibody formation, these results suggest a role for APRIL/TACI interactions in the generation of this response. Taken together, our data indicate that APRIL is involved in the induction and/or maintenance of T and B cell responses.
Jens V. Stein, Marta López-Fraga, Fernando A. Elustondo, Carla E. Carvalho-Pinto, Dolores Rodríguez, Ruth Gómez-Caro, Joan de Jong, Carlos Martínez-A, Jan Paul Medema, Michael Hahne
Estrogen is thought to contribute to the increased frequency of autoimmune disorders occurring in females, but a molecular basis for its effects on autoimmunity remains to be elucidated. We have shown previously that estrogen leads to the survival and activation of autoreactive cells in the naive repertoire. To identify the molecular pathways involved in B cell tolerance, we sought to identify genes that are differentially regulated by estrogen in mouse B cells. Several genes involved in B cell activation and survival, including cd22, shp-1, bcl-2, and vcam-1, were upregulated by estrogen in B cells. We found that overexpression of CD22 and SHP-1 in B cells decreased B cell receptor signaling. Estrogen receptors α and β are expressed on B cells and are functional, since they can directly upregulate expression of CD22, SHP-1, and Bcl-2. Estrogen treatment protected isolated primary B cells from B cell receptor–mediated apoptosis. These results suggest that estrogen induces a genetic program that alters survival and activation of B cells in a B cell–autonomous fashion and thus skews the naive immune system toward autoreactivity.
Christine M. Grimaldi, James Cleary, A. Selma Dagtas, Dariush Moussai, Betty Diamond
Copolymer 1 (Cop 1, Copaxone [Teva Marion Partners, Kansas City, Missouri, USA]), a random amino acid copolymer of tyrosine (Y), glutamic acid (E), alanine (A), and lysine (K), reduces the frequency of relapses by 30% in relapsing-remitting multiple sclerosis (MS) patients. In the present study, novel random four–amino acid copolymers, whose design was based on the nature of the anchor residues of the immunodominant epitope of myelin basic protein (MBP) 85-99 and of the binding pockets of MS-associated HLA-DR2 (DRB1*1501), have been synthesized by solid-phase chemistry. Poly (Y, F, A, K) (YFAK) inhibited binding of the biotinylated MBP 86-100 epitope to HLA-DR2 molecules more efficiently than did either unlabeled MBP 85-99 or any other copolymer including Cop 1. Moreover, YFAK and poly (F, A, K) (FAK) were much more effective than Cop 1 in inhibition of MBP 85-99–specific HLA-DR2–restricted T cell clones. Most importantly, these novel copolymers suppressed experimental autoimmune encephalomyelitis, induced in the susceptible SJL/J (H-2s) strain of mice with the encephalitogenic epitope PLP 139-151, more efficiently than did Cop 1. Thus, random synthetic copolymers designed according to the binding motif of the human immunodominant epitope MBP 85-99 and the binding pockets of HLA-DR2 might be more beneficial than Cop 1 in treatment of MS.
Masha Fridkis-Hareli, Laura Santambrogio, Joel N.H. Stern, Lars Fugger, Celia Brosnan, Jack L. Strominger
Dendritic cell–based (DC-based) immunotherapy represents a promising approach to the prevention and treatment of many diseases, including cancer, but current strategies have met with only limited success in clinical and preclinical studies. Previous studies have demonstrated that a TAT peptide derived from the HIV TAT protein has the ability to transduce peptides or proteins into various cells. Here, we describe the use of TAT-mediated delivery of T cell peptides into DCs to prolong antigen presentation and enhance T cell responses. While immunization of mice with DCs pulsed with an antigenic peptide derived from the human TRP2 protein generated partial protective immunity against B16 tumor, immunization with DCs loaded with a TAT-TRP2 peptide resulted in complete protective immunity, as well as significant inhibition of lung metastases in a 3-day tumor model. Although both DC/TRP2 and DC/TAT-TRP2 immunization increased the number of TRP2-specific CD8+ T cells detected by Kb/TRP2 tetramers, T cell activity elicited by DC/TAT-TRP2 was three- to tenfold higher than that induced by DC/TRP2. Furthermore, both CD4+ and CD8+ T cells were required for antitumor immunity demonstrated by experiments with antibody depletion of subsets of T cells, as well as with various knockout mice. These results suggest that a TAT-mediated antigen delivery system may have important clinical applications for cancer therapy.
Helen Y. Wang, Tihui Fu, Gang Wang, Gang Zeng, Donna M. Perry-Lalley, James C. Yang, Nicholas P. Restifo, Patrick Hwu, Rong-Fu Wang
The Th1 cytokines IL-2 and IFN-γ, which inhibit T cell proliferation and promote activation induced cell death, may be required to diminish alloreactive T cell numbers and to foster tolerance across full allogeneic barriers. However, we hypothesized that these cytokines might be dispensable when the alloreactive T cell clone size is relatively small, as is seen in recipients of minor-mismatched grafts. We show that alloreactive T cell clone size of C57BL/6 mice against multiple minor-mismatched 129X1/sv mice was ∼4–9-fold smaller than that against MHC-mismatched BALB/c mice. In the MHC-mismatched combination, CD28-B7 blockade by CTLA4Ig induced long-term graft survival in wild-type recipients, but this treatment was ineffective in IFNγ–/– or IL-2–/– recipients. In contrast, in the minor-mismatched combination, CTLA4Ig induced long-term allograft survival in wild-type, IFNγ–/–, and IL-2–/– recipients. Bcl-xL transgenic animals, which are defective in "passive" T cell death, are likewise sensitive to the effects of CTLA4Ig only in the setting of the minor-mismatch grafts. Therefore, the alloreactive T cell clone size is an important determinant affecting the need for Th1 cytokines and T cell death in tolerance induction. These data have implications for the design of tolerance strategies in transplant recipients with varying degrees of MHC mismatching.
Koji Kishimoto, Sigrid Sandner, Jaime Imitola, Masayuki Sho, Yongsheng Li, Peter B. Langmuir, David M. Rothstein, Terry B. Strom, Laurence A. Turka, Mohamed H. Sayegh
To mount an effective immune response, T cells must divide in response to antigen contact. To maintain tolerance, mucosal lamina propria T cells (LPTs) may adapt their cycling to an antigen-rich gut stimulatory environment. Here, we compared the cell cycle kinetics of LPTs and peripheral blood T cells (PBTs) before and after CD3- and CD2-mediated activation. While CD3-activated naive (CD45RA+) and memory (CD45RO+) PBTs peaked in the S and G2/M phase at 2–3 days, CD3-activated LPTs peaked at 4–6 days. In contrast, CD2 activation induced modest PBT but vigorous LPT cycling. The doubling time of CD3-activated PBTs was 1 day, while that of CD3- or CD2-activated LPTs was 2 days. LPTs failed to upregulate cyclin-dependent kinase 4 and cyclin D3, but Rb phosphorylation and cyclin A and B1 upregulation were induced by CD2 engagement. The extents of clonal expansion in LPT and PBT were comparable, indicating that LPTs’ slow replication delays but does not hinder cell division. CD2-activated LPTs displayed a striking upregulation of p53, whose blockade by antisense oligonucleotides accelerated their S phase transit time to that of CD3-activated PBTs. By slowing LPT cycling, p53 may act as a negative regulator of mucosal immunity, promoting immunological tolerance by preventing excessive T cell replication.
Andreas Sturm, Jugoh Itoh, James W. Jacobberger, Claudio Fiocchi
Vissia Viglietta, Sally C. Kent, Tihamer Orban, David A. Hafler
To understand the relationship between host antigen-presenting cells (APCs) and donor T cells in initiating graft-versus-host disease (GVHD), we followed the fate of host dendritic cells (DCs) in irradiated C57BL/6 (B6) recipient mice and the interaction of these cells with minor histocompatibility antigen- (miHA-) mismatched CD8+ T cells from C3H.SW donors. Host CD11c+ DCs were rapidly activated and aggregated in the T cell areas of the spleen within 6 hours of lethal irradiation. By 5 days after irradiation, <1% of host DCs were detectable, but the activated donor CD8+ T cells had already undergone as many as seven divisions. Thus, proliferation of donor CD8+ T cells preceded the disappearance of host DCs. When C3H.SW donor CD8+ T cells were primed in vivo in irradiated B6 mice or ex vivo by host CD11c+ DCs for 24–36 hours, they were able to proliferate and differentiate into IFN-γ–producing cells in β2-microglobulin–deficient (β2m–/–) B6 recipients and to mediate acute GVHD in β2m–/– → B6 chimeric mice. These results indicate that, although host DCs disappear rapidly after allogeneic bone marrow transplantation, they prime donor T cells before their disappearance and play a critical role in triggering donor CD8+ T cell–mediated GVHD.
Yi Zhang, Jean-Pierre Louboutin, Jiang Zhu, Adam J. Rivera, Stephen G. Emerson
Toll-like receptor 2 (TLR2) and TLR4 play important roles in the early innate immune response to microbial challenge. To clarify the functional roles of TLRs 2 and 4 in mast cells, we examined bone marrow–derived mast cells (BMMCs) from TLR2 or TLR4 gene-targeted mice. Peptidoglycan (PGN) from Staphylococcus aureus stimulated mast cells in a TLR2-dependent manner to produce TNF-α, IL-4, IL-5, IL-6, and IL-13, but not IL-1β. In contrast, LPS from Escherichia coli stimulated mast cells in a TLR4-dependent manner to produce TNF-α, IL-1β, IL-6, and IL-13, but not IL-4 nor IL-5. Furthermore, TLR2- but not TLR4-dependent mast cell stimulation resulted in mast cell degranulation and Ca2+ mobilization. In a mast cell–dependent model of acute sepsis, TLR4 deficiency of BMMCs in mice resulted in significantly higher mortality because of defective neutrophil recruitment and production of proinflammatory cytokines in the peritoneal cavity. Intradermal injection of PGN led to increased vasodilatation and inflammation through TLR2-dependent activation of mast cells in the skin. Taken together, these results suggest that direct activation of mast cells via TLR2 or TLR4 by respective microligands contributes to innate and allergic immune responses.
Volaluck Supajatura, Hiroko Ushio, Atsuhito Nakao, Shizuo Akira, Ko Okumura, Chisei Ra, Hideoki Ogawa
Leukotrienes are lipid mediators that evoke primarily proinflammatory responses by activating receptors present on virtually all cells. The production of leukotrienes is tightly regulated, and expression of 5-lipoxygenase, the enzyme required for the first step in leukotriene synthesis, is generally restricted to leukocytes. Arachidonic acid released from the cell membrane of activated leukocytes is rapidly converted to LTA4 by 5-lipoxygenase. LTA4 is further metabolized to either LTC4 or LTB4 by the enzyme LTC4 synthase or LTA4 hydrolase, respectively. Unlike 5-lipoxygenase, these enzymes are expressed in most tissues. This observation previously has led to the suggestion that LTA4 produced by leukocytes may, in some cases, be delivered to other cell types before being converted into LTC4 or LTB4. While in vitro studies indicate that this process, termed transcellular biosynthesis, can lead to the production of leukotrienes, it has not been possible to determine the significance of this pathway in vivo. Using a series of bone marrow chimeras generated from 5-lipoxygenase– and LTA4 hydrolase–deficient mice, we show here that transcellular biosynthesis contributes to the production of leukotrienes in vivo and that leukotrienes produced by this pathway are sufficient to contribute significantly to the physiological changes that characterize an ongoing inflammatory response.
Jean-Etienne Fabre, Jennifer L. Goulet, Estelle Riche, MyTrang Nguyen, Kenneth Coggins, Steven Offenbacher, Beverly H. Koller