Biomedical subjects

A Valujskikh

Publications and source records attributed to A Valujskikh.

11 recordsLinked to original sources

PubMed2006

The challenge of inhibiting alloreactive T-cell memory.

Memory T cells specific for donor antigens present a unique challenge in transplantation. In addition to expressing rapid and robust immune responses to a transplanted organ, memory T cells may be resistant to the effects of currently used graft-prolonging therapies. The increasing recognition that alloreactive memory T cells participate in transplant rejection is driving new lines of research focusing on understanding the immunobiology of alloreactive memory T cells and on designing novel therapies to specifically target memory T cells. The purpose of this review is to summarize the effects of existing immunosuppressive drugs and costimulatory blockade on functions of alloreactive memory T cells that undermine allograft survival.

Animals↗

PubMed2001

In vivo blockade of macrophage migration inhibitory factor prevents skin graft destruction after indirect allorecognition.

BACKGROUND: The effector mechanisms that ultimately destroy transplanted tissues are poorly understood. In particular, it is not clear how CD4+ T cells primed to donor-derived determinants expressed on recipient MHC molecules (the indirect pathway) can mediate graft destruction in the absence of cognate recognition of peptide: MHC on the graft cells themselves. Macrophage migration inhibitory factor (MIF) inhibits macrophage movement and is a proinflammatory and regulatory cytokine known to be essential for development of delayed-type hypersensitivity reactions. METHODS: To test whether MIF participates in graft destruction following indirect recognition, we studied rejection of MHC-II-deficient skin grafts placed on allogeneic SCID recipients adoptively transferred with naïve CD4+ T cells, and the recipients were treated with neutralizing anti-MIF monoclonal antibody or isotype control IgG. In this model graft rejection can only occur indirectly as the graft cells lack MHC II for recognition by the recipient CD4+ T cells. RESULTS: We found that in vivo blockade of MIF inhibited indirect CD4+ cell-mediated skin graft destruction, and markedly reduced detectable macrophages within the grafts. The neutralizing anti-MIF antibody significantly inhibited alloreactive DTH but did not prevent T cell priming or interferon-gamma release by primed T cells. CONCLUSIONS: The results strongly implicate MIF as an active participant in skin graft destruction after indirect recognition and suggest that this effect is mediated through an inhibition of macrophage migration and/or function.

Animals↗

PubMed2001

A role for TGFbeta and B cells in immunologic tolerance after intravenous injection of soluble antigen.

BACKGROUND: Intravenous injection of soluble antigen has been reported to induce immunologic tolerance through a variety of mechanisms including T-cell deletion, anergy, and suppression. To clarify the reported discrepancies, we studied mechanisms of intravenous tolerance to a defined transgenic minor transplantation antigen in mice. METHODS: Wild-type C57BL/6 (B6) mice or congenic B6 B-cell knockout mice were made tolerant to beta-galactosidase (beta-gal). Clinical tolerance was assessed by placement of B6 beta-gal transgenic (tg) and third-party skin grafts. In vitro analysis of T- and B-cell immunity and in vivo treatment with anti-TGFbeta antibodies were used to define mechanisms of induced tolerance. RESULTS: Intravenous injection of beta-gal induced true immunologic tolerance to beta-gal tg skin in wild-type but not in B-cell-deficient recipients, suggesting that antigen presentation by B cells was required for the effect. The tolerogenic manipulation primed a population of CD4+, beta-gal-specific, TGFbeta-producing T cells. Although evidence for both anergy and suppression were observed, subsequent data demonstrated that TGFbeta was a critical immunoregulatory mediator of the tolerant state: neutralizing anti-TGFbeta antibodies fully prevented the induction of tolerance to B6 beta-gal tg skin grafts. Second male beta-gal tg grafts placed onto female recipients that were previously made tolerant to female beta-gal tg skin were rapidly rejected, however, suggesting that this TGFbeta-induced tolerance could not be linked to additional antigenic determinants. CONCLUSIONS: The studies demonstrate a critical role for TGFbeta in mediating tolerance after intravenous injection of antigen but additionally raise concerns about the stability of this tolerant state.

Animals↗

PubMed2001

Indirectly primed CD8+ T cells are a prominent component of the allogeneic T-cell repertoire after skin graft rejection in mice.

BACKGROUND: Alloreactive CD4 and CD8 T lymphocytes recognize antigen through both the direct and the indirect pathways. Although indirect priming of CD4+ T cells has been well described, little is known about the frequency and cytokine profile of indirectly primed CD8+ T cells during fully allogeneic graft rejection. METHODS: We used a cytokine enzyme-linked immunosorbent spot assay to characterize indirect priming of alloreactive CD8 and CD4 cells in mice. RESULTS: Interferon-gamma-producing CD8+ T cells specific for indirectly presented alloantigen were detectable in allograft-primed mice at a frequency of 50-100 per million cells (compared with 3000 per million for responses through the direct pathway) and were similar in frequency to indirectly primed CD4 cells. CONCLUSION: CD8+ T cells primed through the indirect pathway are a prominent component of the alloreactive T-cell repertoire induced after skin graft placement in mice, raising the possibility that these cells may play a significant role in the rejection process itself.

Animals↗

PubMed2000

Comprehensive assessment of determinant specificity, frequency, and cytokine signature of the primed CD8 cell repertoire induced by a minor transplantation antigen.

T cell immunity is often focused on one peptide segment of a complex protein Ag, with other epitopes inducing weaker, low frequency responses or no responses at all. Such determinant hierarchy has been well characterized for MHC class II-restricted CD4 cell immunity, but is less well understood for class I-restricted CD8 cell responses. We studied class I determinant recognition in a skin transplant model with beta-galactosidase (beta-gal) as a minor transplantation Ag. CD8 T cells from C57BL/6 mice that rejected congenic C57BL/6 beta-gal transgenic skin were tested in enzyme-linked immunospot assays for recall responses to single-step, overlapping, 9-mer peptides that spanned a 94-aa region of the beta-gal sequence. This approach provided every possible class I-restricted peptide for CD8 cell recognition, allowing us to define the in vivo frequency of CD8 cells specific for each of the 86 individual peptides. While four peptides were predicted to bind to the Kb or Db molecules, only one (beta-gal96-103) actually induced an immune response. No peptides outside of the motifs were recognized. Tolerization to beta-gal96-103 significantly prolonged beta-gal transgenic skin graft survival, confirming its immune dominance. Therefore, single-determinant dominance characterized this CD8 cell response. The data demonstrate the feasibility of large-scale, comprehensive, class I determinant mapping, an approach that should be indispensable in measuring CD8 cell immunity in humans.

Amino Acid Motifs↗

PubMed2000

CD4+ T cells responsive through the indirect pathway can mediate skin graft rejection in the absence of interferon-gamma.

BACKGROUND: T cells responding through the indirect pathway can induce allograft rejection, but mechanisms of rejection are not known. Interferon-y (IFN-gamma) may be an important mediator of rejection under these circumstances. METHODS: We transferred CD4+ T cells from IFN-gamma-deficient (IFN-gamma-/-) mice into SCID recipients of MHC II-deficient (MHC II-/-) skin grafts. Under these conditions, rejection can only occur via the indirect pathway and cannot be mediated by T-cell production of IFN-gamma. RESULTS: IFN-gamma-/- CD4+ T cells rejected MHC II -/- skin grafts. Flow cytometry revealed only CD4+ T cells in the recipients. Cytokine enzyme-linked immunosorbent spot assays confirmed only indirect recognition with an associated expansion of an alloreactive population of IL-2-, IL-4-, and IL-5-secreting T cells. CONCLUSION: CD4+ T cells recognizing alloantigens via the indirect pathway can mediate skin graft rejection in the absence of IFN-gamma.

Animals↗

PubMed1999

Characterization and manipulation of T cell immunity to skin grafts expressing a transgenic minor antigen.

BACKGROUND: Minor histocompatibility antigens play a significant role in allograft rejection when donor and recipient are matched at MHC loci. An improved understanding of T cell immunity directed toward a model minor antigen may provide new approaches for preventing graft rejection. METHODS: C57BL/6 (B6) recipient mice were engrafted with skin from B6 beta-galactosidase transgenic (beta-gal tg) donors and the induced T cell immune responses were characterized by cytokine ELISA spot assay. beta-gal-specific immunity was manipulated prior to transplant through preinjection with beta-gal in complete Freund's adjuvant (CFA) or through preinjection with soluble beta-gal i.v. RESULTS: B6 mice rejected beta-gal tg skin by day 25. Rejection was associated with a low frequency of predominantly CD8+, interferon-gamma-producing T cells capable of directly recognizing both beta-gal tg cells and an immunodominant major histocompatibility complex I-restricted peptide derived from the beta-gal protein. Rejection of multiple minor antigen disparate skin and major histocompatibility complex-disparate skin occurred significantly faster, and was associated with a 10- to 30-fold higher frequency of alloreactive T cells, than rejection of beta-gal tg skin. Prepriming of recipients with beta-gal in complete Freund's adjuvant resulted in an increased frequency of beta-gal-specific T cells and accelerated rejection of beta-gal tg skin. Intravenous injection of soluble beta-gal-induced graft tolerance and a lack of detectable beta-gal-specific immunity. CONCLUSIONS: The findings reveal that transgenically expressed beta-gal behaves as a minor transplantation antigen and that manipulation of the beta-gal-specific T cell repertoire can dramatically affect rejection of beta-gal tg skin grafts. The work provides the foundation for mechanistic studies of tolerogenesis to minor antigenic determinants.

Animals↗

PubMed1999

Contributions of direct and indirect T cell alloreactivity during allograft rejection in mice.

The immune response to transplanted allogeneic tissues is mediated by T cells that recognize donor histocompatibility Ags either via direct (donor MHC and peptides) or indirect (recipient MHC and donor-derived peptides) allorecognition pathways. The relative contribution of each of these pathways to allograft rejection remains largely unknown. To address this, we used an enzyme-linked immunospot assay to define the frequency and cytokine phenotype of T cells responding via direct and indirect pathways to alloantigens at various time points following placement of allogeneic B10.A skin grafts on BALB/c recipient mice. During acute graft rejection >90% of the anti-B10.A T cell repertoire was directed toward intact donor MHC molecules, while T cells recognizing indirectly presented, donor-derived peptides accounted for <10%. This indirect response was comprised of reactivity toward both MHC-derived and, to a lesser extent, minor Ag-derived determinants. The direct and indirect alloresponses were predominantly detected in recipient lymph nodes and were mediated by T cells displaying a mixed type 1/type 2 cytokine phenotype. Six weeks following rejection, however, the memory allospecific T cell response became predominant in the recipient spleen, with only minimal activity detectable in the draining lymph nodes. This work provides a new approach for analysis of the immunophysiology of allograft rejection and should be useful for monitoring immune responses to graft Ags in human transplant recipients.

Animals↗

PubMed1998

Type 2 immune deviation has differential effects on alloreactive CD4+ and CD8+ T cells.

Allograft rejection has been associated with detection of the type 1 lymphokines, IFN-gamma and IL-2. The role of type 2 cytokines (IL-4 and IL-5) remains controversial, as is whether alloreactive CD4+ and CD8+ T cells behave similarly when exposed to type 2 cytokine-enhancing manipulations. We studied the characteristics of alloreactive CD4+ and CD8+ T cells before and after type 2 immune deviation induced by IL-4 plus anti-IFN-gamma Ab. Alloreactive T cells from naive mice were low in frequency, produced only IL-2, and were predominantly CD4+, while alloreactive T cells from allograft-primed mice were high in frequency, produced IFN-gamma, IL-2, and IL-4, and were predominantly CD8+. Type 2 immune deviation of allospecific CD4+ T cells resulted in IL-4 and IL-5 production without IFN-gamma, consistent with unipolar type 2 immunity. These T cells mediated delayed-type hypersensitivity, but not cytotoxicity. Under identical type 2 cytokine-inducing conditions, allospecific CD8+ T cells were primed to become IL-4, IL-5, and IFN-gamma producers, and exhibited cytotoxicity, but not classic delayed-type hypersensitivity. Adoptive transfer of either cell population into SCID recipients of allogeneic skin resulted in graft rejection, with stable allospecific type 2 cytokine production in vivo. Adoptive transfer of the IL-4/IL-5-producing CD4+ T cells, but not the CD8+ T cells, induced a distinct histopathology characterized by marked eosinophilic infiltration of the skin. We conclude that type 2 immune deviation has differential effects on CD4+ and CD8+ T cells and results in emergence of alternate effector mechanisms capable of destroying allografts.

Animals↗

PubMed1998

T cells reactive to a single immunodominant self-restricted allopeptide induce skin graft rejection in mice.

Alloreactive T lymphocytes can respond to foreign MHC complexed with foreign peptides through the direct pathway of allorecognition and can additionally recognize allopeptides expressed in the context of recipient (self) MHC through the indirect pathway. To better elucidate how indirect pathway-responsive CD4(+) T cells mediate allograft rejection, we isolated and characterized a TH1 T cell line from BALB/c recipients of B10.A skin that responds to a defined immunodominant, self-restricted allopeptide, I-Abetak58-71. When transferred into BALB/c severe combined immunodeficiency recipients of B10.A skin allografts, this cell line specifically induced a form of skin graft rejection characterized by the presence of TH1 cytokines, macrophage infiltration, and extensive fibrosis. Recall immune responses and immunofluorescence of the rejecting skin revealed only the presence of the peptide-specific T cells within the recipient animals, with no evidence of a direct pathway alloresponse. These studies demonstrate that T cells reactive to a single self-restricted allopeptide can mediate a form of allogeneic skin graft rejection that exhibits characteristics of a chronic, fibrosing process.

Animals↗

PubMed1995

Influence of synthetic peptides, corresponding to fragments of the human alpha-2 interferon molecule, on the proliferation of lymphoblastoid cells in vitro. Growth inhibition and receptor binding.

Influence of nine synthetic peptides from the C-terminal part of human alpha-2 interferon (IFN) molecule on growth of a human T-lymphoblastoid cell line MT-4 was investigated. It was shown that some peptides inhibited the proliferation of MT-4 cells. It was also found that MT-4 cells expressed specific receptors on the outer surface of the plasma membrane. All studied peptides competed for binding to a common binding site. Antiproliferative activity of the peptides correlated with their length and affinity to receptors on the outer membrane of MT-4 cells.

Amino Acid Sequence↗