Cell-mediated graft rejection observed in two lines of human histocompatibility leukocyte antigen class I transgenic mice

Intrathymic inoculation of donor HLA class I-derived peptide generates donor-specific CD4+CD25+ regulatory T cells

CD4(+)CD25(+) regulatory T cells are selected in the thymus to control autoreactive thymic escapees preventing autoimmunity that cannot be achieved by negative selection or deletion alone, thus playing an important role in the maintenance of immunological homeostasis. Not only significant in preventing autoimmunity, CD4(+)CD25(+) regulatory T cells have also been shown to be involved in allograft tolerance in organ transplantation. We have formerly introduced two lines of HLA class I transgenic mice to elucidate the role of HLA class I molecules in transplantation biology. Using a heterotopic cardiac transplantation model, we show herein that intrathymic inoculation of donor HLA class I-derived synthetic peptide results in the generation of CD4(+)CD25(+) regulatory T cells, which induce graft specific tolerance without any preconditioning of the recipient or use of immunosuppressive drugs. This study provides evidence of the novel therapeutic potential of CD4(+)CD25(+) regulatory T cells for clinical transplantation.

Graft coronary artery disease in murine cardiac allografts: proposal to meet the need for standardized assessment

BACKGROUND

Inconsistency exists in assessing the severity of graft coronary artery disease (GCAD) in studies that use mouse models. The central issue associated with this inconsistency is the lack of a standardized approach for assessing mouse GCAD.

METHODS

We propose a new histologic definition of GCAD based on 3 successive stages (endotheliitis, premature lesion, and mature lesion) that mark the progression of this condition. In addition to these qualitative measures of GCAD, we propose including 2 additional morphometric parameters (percentage of luminal narrowing and intima-to-media ratio) and a measure of distribution (percentage of affected vessels) in the routine quantification of GCAD.

RESULTS

We introduce 2 new mouse models of GCAD as examples that satisfy these criteria.

CONCLUSION

The proposed assessment criteria may simplify data collection and interpretation of results in various models of GCAD.

Maturation of antigen-presenting cells is compromised in HLA-G transgenic mice

The human MHC class Ib antigen HLA-G is thought to regulate maternal immune responses during pregnancy. Here we show that expression of HLA-G in transgenic mice diminished cellular immunity by inhibiting maturation of myelomonocytic cells into functional antigen-presenting cells (APC). Skin allografts applied to HLA-G transgenic mice survived longer and resultant T cell responses were less potent compared to control mice. T cells from HLA-G mice responded normally to allogeneic APC and immunohistological analyses of spleen revealed no marked abnormalities. However, spontaneous outgrowths of myeloid cells were observed when bone marrow or splenocytes from HLA-G mice were cultured in vitro, but functionally competent APC did not develop spontaneously in bone marrow cultures supplemented with granulocyte macrophage colony stimulating factor (GM-CSF). Addition of lipopolysaccharide (LPS) to GM-CSF-derived bone marrow cultures rescued APC maturation. Studies using HLA-G tetrameric reagents revealed that HLA-G-specific binding activity was associated with CD11c(+) myelomonocytic cells, while binding to lymphoid and NK cell subsets was undetectable. These data show that spontaneous maturation of functionally competent dendritic cells (DC) is compromised in HLA-G mice. We hypothesize that HLA-G inhibits maturation of DC via receptor-mediated interactions with myelomonocytic precursors, which render immature DC precursors unable to receive signals from activated T cells.

Allogenicity of cryopreserved human fibroblasts: cryopreservation does not downregulate the allogenicity of fibroblasts making up the matrices of allografts

BACKGROUND

Although cryopreserved tissue allografts are being widely used, long-term degeneration of implanted cryopreserved allografts has become a problem. Although immunologic rejection has been suggested to play a part in this degeneration, cryopreserved allografts are considered to be less immunogenic than fresh allografts.

OBJECTIVE

We investigated the effect of cryopreservation on the allogenicity of the fibroblasts that make up the matrices of allografts.

METHODS

Fibroblast cell strains obtained from surgically resected lung specimens were used. Allogenicity-related antigens expressed on the cell surface (human leukocyte antigen 1, human leukocyte antigen 2, and intercellular adhesion molecule 1), stimulation indices during 1-way mixed lymphocyte-fibroblast cell culture, and proliferation indices of freshly passaged fibroblasts and cryopreserved fibroblasts stored for 1, 4, and 24 weeks were examined. Flow cytometric analysis with monoclonal antibodies was used to test for cell surface antigens, and a colorimetric methyl-thiazol-diphenyl-tetrazolium assay was used to assess stimulation indices and fibroblast proliferation indices. The effect of exogenous interferon-gamma on the degree of expression of human leukocyte antigen 1, human leukocyte antigen 2, and intercellular adhesion molecule 1 was examined simultaneously.

RESULTS

The proliferation indices of fibroblasts were well maintained by cryopreservation. Expression of human leukocyte antigen 1, human leukocyte antigen 2, and intercellular adhesion molecule 1 by fibroblasts was significantly upregulated by interferon-gamma, and cryopreservation did not downregulate this expression.

CONCLUSION

Our study suggests that although the fibroblast cell component may be beneficial in restoring allograft function properties initially, it may render the implanted allograft more immunogenic, ultimately resulting in greater rejection and inflammatory responses by the host and, in turn, degeneration of the graft.