HLA-restricted T-cell recognition of Epstein-Barr virus-infected B cells

In mice the cytotoxic T-cell response to several types of virus is influenced by genes within the major histocompatibility complex; in particular, genetic control is exercised at the effector cell level through a requirement that virus-specific cytotoxic T cells recognise viral antigens in association with H-2K and H=2D region gene products on the surface of infected cells. In man the restriction which the analogous HLA-A, -B and -C-region gene products might place on virus-specific T-cell function is still in dispute. The earliest and most controversial evidence concerns the Epstein-Barr virus (EBV), a B lymphotropic agent which causes infectious mononucleosis (IM) and which induces an unusually vigorous T-cell response; cytotoxic T cells from IM patients' blood were shown to be EBV-specific yet, in contrast to mouse systems, apparently free of any obvious HLA restriction. Since then T-cell recognition of EBV-infected B cells has assumed particular significance as a model system for the study of cytotoxic T-cell function in man. This report describes the results of a new approach clearly indicating that HLA-A and -B region products do indeed have a role in this system.     

Strong xenogeneic HLA response in transgenic mice after introducing an alpha 3 domain into HLA B27.

The pronounced response by mouse T cells to the major histocompatibility complex (MHC) class I antigens of the same species is characterized by a relatively large fraction of responding cells. Responses to MHC class I allelles of other species are, however, generally much weaker. T lymphocytes are positively selected on thymic MHC antigens, resulting in a T-cell repertoire with strong alloreactivity. This has been explained in terms of a mouse T-cell repertoire that is not efficiently selected for recognition of HLA molecules owing to the absence of HLA in mice. Here we show that mice transgenic for HLA mount a T-cell response against allogeneic HLA that is no better than in normal mice. We decided instead to test whether the mouse accessory molecule Lyt-2 on cytotoxic T lymphocytes could interact efficiently with the alpha 3 domain of HLA. To do this, we replaced the alpha 3 domain of HLA-B27 by a murine alpha 3 domain in a gene construct used to produce transgenic mice, and then used the spleen cells from these mice to stimulate normal mouse T cells. Under these conditions cytotoxic T lymphocytes were generated with the same frequency against xenogeneic HLA-B27 determinants as against allogeneic mouse class I antigens. These findings indicate that the normally weak xeno-MHC response is due to the inefficient interaction of the murine Lyt-2 accessory molecule with HLA class I, and not to limitations of the mouse T-cell repertoire.     

Murine cells expressing an HLA molecule are specifically lysed by HLA-restricted antiviral human T cells

Class I HLA (histocompatibility locus antigen) molecules are the targets of allospecific cytolytic T lymphocytes (CTL) in graft rejection, and constitute the restricting elements necessary for the interaction between antiviral CTL and virus-infected cells. Cells expressing only one HLA in the absence of other human molecules would provide a remarkable model for studying the function of these molecules. However, HLA+ murine cells transfected with human genes are generally not lysed by allospecific human CTL, and this is ascribed to insufficient HLA expression, lack of human beta 2-microglobulin, alteration of HLA molecules or absence of receptors for human T8 or LFA1 molecules in murine cells. Here we report, for the first time, the specific lysis of virus-infected HLA+ murine cells by HLA-restricted antiviral human CTL. Therefore, these murine cells constitute an excellent model for studying the role of HLA molecules.     

MHC antigens in urine as olfactory recognition cues

The classical class I antigens of the major histocompatibility complex (MHC) are cell-surface glycoproteins which were originally discovered because they cause rapid rejection of cells or tissues grafted between unrelated individuals. These molecules are encoded by the K, D and L loci of the mouse MHC (and analogous loci in other species) which show extreme species polymorphism and a large number of alleles. In an outbreeding population 3.6 X 10(9) unique MHC class I phenotypes can be encoded by the 100 alleles at each of the K and D loci and the 6 alleles at the L locus. This level of polymorphism ensures that the cells and tissues of each unrelated individual are uniquely identified by their class I membrane-bound antigens. Like other membrane bound proteins, these class I molecules are anchored in the lipid bilayer by a hydrophobic domain encoded by exon 5. However, there have been reports of the occurrence of classical class I molecules in true solution in the blood of humans, mice, and rats. We report here that classical polymorphic class I molecules in normal rats are constitutively excreted in the urine and that untrained rats can distinguish the smell of urine samples taken from normal donors that differ only at the class I MHC locus and therefore excrete different allelomorphs of class I molecules in their urine.     

Virus-induced autoantibody response to a transgenic viral antigen

The induction of autoantibodies and their possible role in the pathogenesis of autoimmune disease are poorly understood. Involvement of infectious agents has been suspected, but direct evidence is sparse. Whether immunological unresponsiveness to self by antibody-forming B cells is maintained by clonal abortion, clonal anergy or suppression, or how the scenario of interactions between helper T cells, B cells and antigen-presenting cells is distorted in autoantibody responses, is being analysed and widely debated. To evaluate tolerance of neutralizing B-cell responses we used transgenic mice expressing the cell membrane associated glycoprotein (G) of vesicular stomatitis virus (VSV) as self-antigen. We show that autoantibodies to VSV-G cannot be induced by VSV-G in adjuvant or by recombinant vaccinia virus expressing VSV-G, but are triggered by infection with wild-type VSV. The data show that helper T-cell tolerance is crucial in maintenance of B-cell non-reactivity and that cognate T-B recognition is necessary to break tolerance of self-reactive B cells. These results may help to understand mechanisms of virus-induced autoimmunity.     

Regulation of human insulin gene expression in transgenic mice

Insulin is a polypeptide hormone of major physiological importance in the regulation of fuel homeostasis in animals (reviewed in refs 1,2). It is synthesized by the beta-cells of pancreatic islets, and circulating insulin levels are regulated by several small molecules, notably glucose, amino acids, fatty acids and certain pharmacological agents. Insulin consists of two polypeptide chains (A and B, linked by disulphide bonds) that are derived from the proteolytic cleavage of proinsulin, generating equimolar amounts of the mature insulin and a connecting peptide (C-peptide). Humans, like most vertebrates, contain one proinsulin gene, although several species, including mice and rats, have two highly homologous insulin genes. We have studied the regulation of serum insulin levels and of insulin gene expression by generating a series of transgenic mice containing the human insulin gene. We report here that the human insulin gene is expressed in a tissue-specific manner in the islets of these transgenic mice, and that serum human insulin levels are properly regulated by glucose, amino acids and tolbutamide, an oral hypoglycaemic agent.     

Prevention of diabetes in non-obese diabetic I-Ak transgenic mice

The non-obese diabetic (NOD) mouse develops insulin-dependent diabetes mellitus (IDDM) with mononuclear cell infiltration of the islets of Langerhans and selective destruction of the insulin-producing beta-cells, as in humans. Most infiltrating cells are T lymphocytes, and most of these carry the CD4 antigen. Adoptive transfer of T cells from diabetic NOD mice into irradiated NOD or athymic nude NOD mice induces diabetes. Susceptibility to IDDM in NOD mice is polygenic, with one gene linked to the major histocompatibility complex class II locus, which in NOD mice expresses a unique I-A molecule but no I-E. Speculation exists as to the role of the I-A molecule in the diabetes susceptibility of NOD mice, especially regarding the significance of specific unique residues. To examine the role of the NOD I-A molecule in IDDM pathogenesis, we made NOD/Lt mice transgenic for I-Ak by microinjecting I-Ak alpha- and beta-genes into fertilized NOD/Lt eggs. Insulitis was markedly reduced and diabetes prevented in NOD/Lt mice expressing I-Ak.     

Common west African HLA antigens are associated with protection from severe malaria

A large case-control study of malaria in West African children shows that a human leucocyte class I antigen (HLA-Bw53) and an HLA class II haplotype (DRB1*1302-DQB1*0501), common in West Africans but rare in other racial groups, are independently associated with protection from severe malaria. In this population they account for as great a reduction in disease incidence as the sickle-cell haemoglobin variant. These data support the hypothesis that the extraordinary polymorphism of major histocompatibility complex genes has evolved primarily through natural selection by infectious pathogens.     

Defective processing and presentation of exogenous antigens in mutants with normal HLA class II genes

Presentation of an exogenous protein antigen to helper (CD4+)T-lymphocytes by antigen presenting cells (APC) generally requires that the APCs degrade the native protein antigen into an immunogenic peptide, a process termed 'antigen processing', and that this peptide bind to a major histocompatibility complex (MHC) class II molecule. The complex of peptide and MHC molecule on the APC surface provides the stimulatory ligand for the alpha beta T cell receptor. The intracellular pathways and molecular mechanisms involved in the generation of the peptide-MHC complex are not well understood. Here, we describe several mutant APCs which are altered in their ability to present native exogenous protein antigens but effectively present immunogenic peptides derived from these proteins. The lesions in these mutants are not in the class II structural genes, but they affect the conformation of mature class II dimers.