The immunogenetics of insulin-dependent diabetes

The Many Faces of CD4+ T Cells: Immunological and Structural Characteristics

As a major arm of the cellular immune response, CD4⁺ T cells are important in the control and clearance of infections. Primarily described as helpers, CD4⁺ T cells play an integral role in the development and activation of B cells and CD8⁺ T cells. CD4⁺ T cells are incredibly heterogeneous, and can be divided into six main lineages based on distinct profiles, namely T helper 1, 2, 17 and 22 (Th1, Th2, Th17, Th22), regulatory T cells (Treg) and T follicular helper cells (Tfh). Recent advances in structural biology have allowed for a detailed characterisation of the molecular mechanisms that drive CD4⁺ T cell recognition. In this review, we discuss the defining features of the main human CD4⁺ T cell lineages and their role in immunity, as well as their structural characteristics underlying their detection of pathogens.

Development of an I-Ag7-expressing antigen-presenting cell line: intrinsic molecular defect in compact I-Ag7 dimer generation

Insulin-dependent diabetes mellitus (IDDM) results from chronic, T-cell dependent, autoimmune destruction of the insulin-producing beta-cells in the Langerhans' islets of the pancreas. Non-obese diabetic (NOD) mice spontaneously develop IDDM that resembles human type I diabetes. The susceptibility to diabetes in the NOD strain is a complex polygenic trait that determines a phenotype of immune alterations. The unique MHC class II molecule expressed by NOD mice (I-Ag7) plays a major role in the development of disease. Recently, it has been reported that I-Ag7 molecules generate a lower proportion of compact alphabeta heterodimers, compared to other haplotypes. However, it is not clear whether this reflects an intrinsic defect of this molecule to bind peptide stably or is the result of abnormal processing and/or peptide loading into the I-Ag7 molecule. Our aim was to develop and characterize a suitable antigen-presenting cell (APC) that expressed I-Ag7 in the context of a non-diabetes-prone antigen processing and presentation machinery. Here, we report the generation of a mouse DAP.3 fibroblast cell line (DAP.3Ag7) that constitutively expresses high levels of I-Ag7. Using DAP.3 cells transfected with I-Ag7 or I-Ak, we show that the expression of compact dimers in the same cell type is proportionally less for I-Ag7 molecules than for I-Ak molecules, implying an intrinsic defect of the I-Ag7 molecule as the cause for the low generation of compact dimers. However, DAP.3Ag7 cells are able to process and present antigen, as indicated by I-Ag7-dependent IL-2 production by a GAD67-specific NDO T-cell hybridoma after stimulation with GAD and live, but not fixed, DAP.3Ag7 cells. The IL-2 response to GAD when presented by DAP.3Ag7 was significantly higher than the response to GAD presented by NOD splenocytes. Based on these data, we conclude that the low generations of compact dimers is an intrinsic feature of I-Ag7 molecules and not affected by other genes in the NOD background. The DAP.3Ag7 cell line should be a valuable tool with which to dissect the role of the I-Ag7 molecule in antigen presentation and T-cell activation in NOD mice, which clearly contributes to the development of IDDM.

Regulation by non-major histocompatibility complex genes of the allo-4-hydroxy-phenylpyruvate dioxygenase (F liver protein) response

Although rapid progress is being made in the quantitative genetics of multifactorial disease, no response to a simple antigen has yet been subjected to full genomic analysis. The well-characterized antigen allo-HPPD (4-hydroxy-phenylpyruvate dioxygenase, previously known as F liver antigen) is a good candidate for such treatment. Old and new data bearing on this possibility are here assembled. In respect of antibody production and an early burst of interleukin-4 (IL-4) transcription, introduction of the non-major histocompatibility complex (MHC) background from A/J strain mice into F1 hybrids with C57BL10 strains up-regulates the response. These findings can be aligned with previous quantitative genetics carried out on airway hyper-responsiveness in related strains, and to a lesser extent with the genetics of autoimmune diabetes in the mouse. Taken together, the findings suggest that regulation of the pro-inflammatory cytokines are largely responsible for the variation. Additional data indicate that these non-MHC genes are are to a variable extent (depending on the response parameter) epistatic to the down-regulatory MHC allele H-2Ab.