Biomedical subjects

Kent P Jensen

Publications and source records attributed to Kent P Jensen.

6 recordsLinked to original sources

PubMed2006

Proinsulin is encoded by an RNA splice variant in human blood myeloid cells.

Genes for peripheral tissue-restricted self-antigens are expressed in thymic and hematopoietic cells. In thymic medullary epithelial cells, self-antigen expression imposes selection on developing autoreactive T cells and regulates susceptibility to autoimmune disease in mouse models. Less is known about the role of self-antigen expression by hematopoietic cells. Here we demonstrate that one of the endocrine self-antigens expressed by human blood myeloid cells, proinsulin, is encoded by an RNA splice variant. The surface expression of immunoreactive proinsulin was significantly decreased after transfection of monocytes with small interfering RNA to proinsulin. Furthermore, analogous to proinsulin transcripts in the thymus, the abundance of the proinsulin RNA splice variant in blood cells corresponded with the length of the variable number of tandem repeats 5' of the proinsulin gene, known to be associated with type 1 diabetes susceptibility. Self-antigen expression by peripheral myeloid cells extends the umbrella of "immunological self" and, by analogy with the thymus, may be implicated in peripheral immune tolerance.

Autoantigens↗

PubMed2005

The insulin A-chain epitope recognized by human T cells is posttranslationally modified.

The autoimmune process that destroys the insulin-producing pancreatic beta cells in type 1 diabetes (T1D) is targeted at insulin and its precursor, proinsulin. T cells that recognize the proximal A-chain of human insulin were identified recently in the pancreatic lymph nodes of subjects who had T1D. To investigate the specificity of proinsulin-specific T cells in T1D, we isolated human CD4(+) T cell clones to proinsulin from the blood of a donor who had T1D. The clones recognized a naturally processed, HLA DR4-restricted epitope within the first 13 amino acids of the A-chain (A1-13) of human insulin. T cell recognition was dependent on the formation of a vicinal disulfide bond between adjacent cysteine residues at A6 and A7, which did not alter binding of the peptide to HLA DR4. CD4(+) T cell clones that recognized this epitope were isolated from an HLA DR4(+) child with autoantibodies to insulin, and therefore, at risk for T1D, but not from two healthy HLA DR4(+) donors. We define for the first time a novel posttranslational modification that is required for T cell recognition of the insulin A-chain in T1D.

Cells, Cultured↗

PubMed2005

A peptide of glutamic acid decarboxylase 65 can recruit and expand a diabetogenic T cell clone, BDC2.5, in the pancreas.

Self peptide-MHC ligands create and maintain the mature T cell repertoire by positive selection in the thymus and by homeostatic proliferation in the periphery. A low affinity/avidity interaction among T cells, self peptides, and MHC molecules has been suggested for these events, but it remains unknown whether or how this self-interaction is involved in tolerance and/or autoimmunity. Several lines of evidence implicate the glutamic acid decarboxylase 65 (GAD-65) peptide, p524-543, as a specific, possibly low affinity, stimulus for the spontaneously arising, diabetogenic T cell clone BDC2.5. Interestingly, BDC2.5 T cells, which normally are unresponsive to p524-543 stimulation, react to the peptide when provided with splenic APC obtained from mice immunized with the same peptide, p524-543, but not, for example, with hen egg white lysozyme. Immunization with p524-543 increases the susceptibility of the NOD mice to type 1 diabetes induced by the adoptive transfer of BDC2.5 T cells. In addition, very few CFSE-labeled BDC2.5 T cells divide in the recipient's pancreas after transfer into a transgenic mouse that overexpresses GAD-65 in B cells, whereas they divide vigorously in the pancreas of normal NOD recipients. A special relationship between the BDC2.5 clone and the GAD-65 molecule is further demonstrated by generation of a double-transgenic mouse line carrying both the BDC2.5 TCR and GAD-65 transgenes, in which a significant reduction of BDC2.5 cells in the pancreas has been observed, presumably due to tolerance induction. These data suggest that unique and/or altered processing of self Ags may play an essential role in the development and expansion of autoreactive T cells.

Adoptive Transfer↗

PubMed2005

An efficient method for cloning human autoantigen-specific T cells.

T-cell clones are valuable tools for investigating T-cell specificity in infectious, autoimmune and malignant diseases. T cells specific for clinically-relevant autoantigens are difficult to clone using traditional methods. Here we describe an efficient method for cloning human autoantigen-specific CD4+ T cells pre-labelled with CFSE. Proliferating, antigen-responsive CD4+ cells were identified flow cytometrically by their reduction in CFSE staining and single cells were sorted into separate wells. The conditions (cytokines, mitogens and tissue culture plates) for raising T-cell clones were optimised. Media supplemented with IL-2+IL-4 supported growth of the largest number of antigen-specific clones. Three mitogens, PHA, anti-CD3 and anti-CD3+anti-CD28, each stimulated the growth of similar numbers of antigen-specific clones. Cloning efficiency was similar in flat- and round-bottom plates. Based on these findings, IL-2+IL-4, anti-CD3 and round-bottom plates were used to clone FACS-sorted autoantigen-specific CFSE-labelled CD4+ T cells. Sixty proinsulin- and 47 glutamic acid decarboxylase-specific clones were obtained from six and two donors, respectively. In conclusion, the CFSE-based method is ideal for cloning rare, autoantigen-specific, human CD4+ T cells.

Autoantigens↗

PubMed2004

CD4+ T cell proliferation in response to GAD and proinsulin in healthy, pre-diabetic, and diabetic donors.

The ability to measure proliferation of autoantigen-specific T cells is critical for the evaluation of cellular immune function. Using a novel, sensitive, CFSE-based assay, we were able to directly quantitate autoantigen-specific CD4(+) T cell proliferation. However, peripheral blood cells from healthy, pre-diabetic and diabetic donors exhibited overlap in responses to glutamic acid decarboxylase (GAD65) and proinsulin (PI). This indicates that autoantigen-induced CD4(+) T cell proliferation in a functionally complex cell population may not discriminate disease in the general population. Clear discrimination was found between diabetic and healthy sibs, suggesting the need to standardize the genetic and environmental background. In addition, the ability of the CFSE assay to allow analysis of the phenotype and function of autoantigen-responsive T cells may improve discrimination.

Blood Donors↗

PubMed2003

A sensitive method for detecting proliferation of rare autoantigen-specific human T cells.

The ability to measure proliferation of rare antigen-specific T cells among many bystanders is critical for the evaluation of cellular immune function in health and disease. T-cell proliferation in response to antigen has been measured almost exclusively by 3H-thymidine incorporation. This method does not directly identify the phenotype of the proliferating cells and is frequently not sufficiently sensitive to detect rare autoantigen-specific T cells. To overcome these problems, we developed a novel assay for antigen-specific human T-cell proliferation. Peripheral blood mononuclear cells (PBMC) were labelled with the fluorescent dye 5,6-carboxylfluorescein diacetate succinimidyl ester (CFSE) and cells that proliferated in response to antigen, with resultant reduction in CFSE intensity, were measured directly by flow cytometry. This assay was more sensitive than 3H-thymidine incorporation and detected the proliferation of rare antigen-specific CD4(+) T cells at 10-fold lower antigen concentrations. It also allowed the phenotype of the proliferating cells to be directly determined. Using the CFSE assay we were able to measure directly the proliferation of human CD4(+) T cells from healthy donors in response to the type 1 diabetes autoantigens glutamic acid decarboxylase (GAD) and proinsulin (PI).

Autoantigens↗