Tissue destruction resulting from the interaction of cytotoxic T cells and their targets

Detection of minor alloantigen-specific cytotoxic T cells after rejection of murine orthotopic corneal allografts: evidence that graft antigens are recognized exclusively via the "indirect pathway"

BACKGROUND

The immune mechanisms by which corneal allografts are rejected in normal ocular graft beds have not been identified. Both acceptors and rejectors of these types of grafts display donor-specific delayed hypersensitivity and in vitro proliferating primed T cells, yet neither develop conventional, donor-specific cytotoxic T cells. We wished to determine whether unconventional donor-specific cytotoxic T cells are generated in rejector mice that recognize donor minor alloantigens presented by recipient major histocompatibility complex (MHC) molecules.

METHODS

BALB/c mice received orthotopic corneal allografts from C57BL/10 donors in normal eyes. At 4 weeks (when 50% of grafts can be designated as rejected), primed cytotoxic T lymphocyte (CTL) activity in draining lymph nodes and spleen was assayed on targets selected to present donor-type minor H antigens on recipient MHC molecules. Control mice received heterotopic corneal allografts and were similarly examined.

RESULTS

Lymphoid organs of recipients that rejected orthotopic or heterotopic corneal allografts contained CTL that lysed targets expressing donor-type minor H antigens presented by recipient MHC molecules. By contrast, no CTL activity was detected from lymphoid cells of recipients that accepted orthotopic corneal allografts. Rejection of orthotopic corneal allografts placed into normal mouse eyes correlates directly with the generation of donor-specific CTL that recognize minor H antigens in the context of recipients MHC molecules.

CONCLUSIONS

These results indicate the indirect pathway of alloantigen presentation is the only pathway operative in the process by which orthotopic corneal allografts are rejected. The roles of emigrant Langerhans cells and corneal lymphatics in the indirect pathway are discussed.

Lymphocyte infiltration following allo- and xenomyoblast transplantation in mdx mice

Human and mouse (C57BL/10SnJ+/+) myoblasts were injected separately in the muscles of C57BL/10ScSn mdx/mdx mice. Mouse myoblasts (C57BL/10SnJ+/+) were also injected in normal mice (C57BL/10SnJ+/+ and BALB/c+/+). Some muscles that received a xenotransplantation (i.e., human myoblasts) were previously injected with a myotoxin, i.e., notexin. This treatment was not used for the allografts (i.e., mouse myoblasts). Human myoblast injections did not increase the number of dystrophin-positive cells above the background level due to backmutation. Moreover, the human myoblasts detected with an anti-HLA antibody decreased rapidly during the 6-week follow-up. The injection of normal mouse myoblasts in mdx mice did, however, increase the number of dystrophin-positive fibers. Moreover, numerous cells expressing mouse MHC class II, macrophages, granulocytes, neutrophils, natural killer cells, and a subset of T lymphocytes were detected by immunohistochemistry in cryostat sections of myoblast-injected muscles. These cells were present within 1 week of the myoblast injection in the muscle regions containing injected human or mouse myoblasts, and progressively decreased during the 6-week follow-up in the human myoblast transplantation. Lymphocyte infiltration reached a significant level following xeno- and alloincompatible transplantations. Antibodies against the human myoblasts and against alloincompatible myoblasts were also detected in the serum of the recipients. These results suggest that humoral and cellular immune reactions are responsible for the poor outcome of myoblast transplantation in mice and could be involved in failure of transplantation in Duchenne muscular dystrophy patients. These results indicate that adequate immunosuppression must be used in these patients.

Predominance of epidermal CD8+ T lymphocytes in bullous cutaneous reactions caused by beta-lactam antibiotics

The phenotype and functional characteristics of skin-infiltrating lymphocytes in beta-lactam antibiotic-induced vesiculobullous exanthemas were studied in vivo and in vitro. Immunohistochemical analysis demonstrated that CD8+ T lymphocytes were the predominant epidermal T-cell subset in these reactions. Epidermal T lymphocytes were isolated and expanded for in vitro studies. Fluorescence-activated cell sorter analysis showed the majority of epidermal T cells to be CD3+, T-cell receptor alpha/beta+, CD4-, CD8+, and HLA-DR+, which correlated with the predominance of epidermal CD8+ T lymphocytes found in situ. Three CD8+ epidermal T-cell clones derived from cutaneous lesions proliferated in response to penicillin-pulsed autologous antigen-presenting cells but not allogeneic antigen-presenting cells, indicating that those clones were antigen and major histocompatibility complex specific. All T-cell clones produced significant amounts of interleukin-2, interferon-gamma, and granulocyte-macrophage colony-stimulating factor. Additionally, the T-cell clones displayed cytotoxicity against epidermal cells in lectin-mediated cytotoxicity and against B-cell lines in T-cell receptor-triggered cytotoxicity. These data demonstrate the presence of epidermal drug-specific CD8+ T cells in bullous drug reactions. Because these CD8+ T cells have a cytotoxic potential, they may contribute to the necrosis of keratinocytes associated with drug-induced blister formation.

What are minor histocompatibility loci? A new look at an old question

In this article, Derry Roopenian relates the traditional view of minor histocompatibility (H) loci to recent advances in understanding of the tissue rejection process and the molecular nature of minor histocompatibility antigens. He proposes that minor H loci can be subdivided by the ability of their products to stimulate different T-cell subsets and discusses the implications of this concept in terms of the origins and behavior of minor H loci and their antigens, tumor immunology and autoimmunity.

Breakdown of blood-brain barrier function in the murine lymphocytic choriomeningitis virus infection mediated by virus-specific CD8+ T cells

Intracerebral inoculation of lymphocytic choriomeningitis virus (LCMV) generally results in a fatal T cell-mediated meningitis. In a previous study we have demonstrated a compromised blood-brain barrier (BBB) under such conditions. Using semi-quantitative radiography and the low molecular tracer 2-amino-[1-14C]isobutyric acid we now demonstrate an uncompromised BBB in i.c. infected T cell-deficient nu/nu mice, but serious dysfunction in heterozygous littermates. Transfer experiments were used to characterize and compare the cell subset(s) involved in inducing BBB dysfunction and fatal disease. It was demonstrated that Thy-1+, CD8+ class I-restricted T cells were mandatory for the increase in BBB permeability as well as for mortality. In addition, depletion of class II-restricted CD4+ cells significantly weakened both effects of cell transfer. These results support the idea of a causal relationship between virus-specific T cell activity, BBB dysfunction, and fatal disease. Furthermore, the data indicate that T helper cells augment the response of LCMV-specific CD8+ effector cells.

Lyme carditis in immunodeficient mice during experimental infection of Borrelia burgdorferi

Recently, we described the severe combined immunodeficiency (scid) mouse as a laboratory model for B. burgdorferi infection. Scid mice inoculated with the virulent low-passage tick isolate Borrelia burgdorferi ZS7 developed a severe pancarditis involving endocardium, myocardium and epicardium in the absence of functional B- or T-cells. Soon after inoculation perivascular infiltration was observed, later diffuse infiltration of the interstitium of the subendocardial and subepicardial areas was seen. The infiltrate was mainly mononuclear and predominantly composed of Mac-1+ cells. Concomitantly, fibroblast proliferation and augmented collagen deposition occurred in the interstitium. This was associated with the presence of B. burgdorferi organisms. The histopathological and ultrastructural findings observed in scid mice resemble those observed in human Lyme carditis. The data emphasize the suitability of the scid mouse as a model in which to study the role of the immune system in the pathogenesis of Lyme carditis.

Evidence that the effector mechanism of skin allograft rejection is antigen-specific

In vivo rejection responses are initiated by specific T-cell recognition of foreign histocompatibility antigens expressed by tissue allografts, but it is not certain if the effector mechanism mediating the actual tissue injury is also antigen-specific. To directly assess the specificity of the effector phase of in vivo rejection responses, we constructed B6 in equilibrium with A/J allophenic mice that are genetic mosaics whose individual cells express either H-2b or H-2a histocompatibility antigens but not both. Trunk skin from B6 in equilibrium with A/J allophenic mice was grafted onto immunoincompetent H-2b nude mice and allowed to heal and regrow hair that was both black and white, reflecting the genetic mosaicism of the allophenic grafts. One month after engraftment, the H-2b nude animals were reconstituted with syngeneic H-2b T cells reactive against H-2a allodeterminants. An obvious rejection response ensued involving antigen-nonspecific inflammatory destruction of the epidermis and complete hair loss. Despite the intensity of the nonspecific inflammatory response, the allophenic skin grafts survived. Importantly, the allophenic grafts regrew hair and the predominant color of that hair was black, providing visual proof that syngeneic B6 melanocytes and hair follicle cells had not been destroyed. Thus, these results demonstrate that although the intense inflammatory component of skin graft rejection responses is capable of damaging superficial epidermal cells nonspecifically, it does not cause rejection of skin allografts. Rather, rejection of skin allografts is mediated by antigen-specific effector T cells that assess individual cells within the dermis of the graft for expression of foreign histocompatibility antigens.