The T cell receptor: its repertoire and role in thymocyte development

The Dendritic Cell Major Histocompatibility Complex II (MHC II) Peptidome Derives from a Variety of Processing Pathways and Includes Peptides with a Broad Spectrum of HLA-DM Sensitivity

The repertoire of peptides displayed in vivo by MHC II molecules derives from a wide spectrum of proteins produced by different cell types. Although intracellular endosomal processing in dendritic cells and B cells has been characterized for a few antigens, the overall range of processing pathways responsible for generating the MHC II peptidome are currently unclear. To determine the contribution of non-endosomal processing pathways, we eluted and sequenced over 3000 HLA-DR1-bound peptides presented in vivo by dendritic cells. The processing enzymes were identified by reference to a database of experimentally determined cleavage sites and experimentally validated for four epitopes derived from complement 3, collagen II, thymosin β4, and gelsolin. We determined that self-antigens processed by tissue-specific proteases, including complement, matrix metalloproteases, caspases, and granzymes, and carried by lymph, contribute significantly to the MHC II self-peptidome presented by conventional dendritic cells in vivo. Additionally, the presented peptides exhibited a wide spectrum of binding affinity and HLA-DM susceptibility. The results indicate that the HLA-DR1-restricted self-peptidome presented under physiological conditions derives from a variety of processing pathways. Non-endosomal processing enzymes add to the number of epitopes cleaved by cathepsins, altogether generating a wider peptide repertoire. Taken together with HLA-DM-dependent and-independent loading pathways, this ensures that a broad self-peptidome is presented by dendritic cells. This work brings attention to the role of "self-recognition" as a dynamic interaction between dendritic cells and the metabolic/catabolic activities ongoing in every parenchymal organ as part of tissue growth, remodeling, and physiological apoptosis.

Multiple sclerosis: sunlight, diet, immunology and aetiology

Multiple sclerosis is more common in temperate latitudes, and migration studies indicate the involvement of an aetiological environmental factor in pre-pubertal life; the precise nature of this factor has never been identified and may perhaps have been overlooked. Here we suggest a simple explanation for the latitude gradient of multiple sclerosis, i.e. that it can be explained by the immunosuppressant effects of sunlight mediated via suppression of the secretion of the immunostimulatory neurohormone melatonin from the pineal gland. The effects of dietary fatty acids in multiple sclerosis also indicate the involvement of anti-inflammatory eicosanoids in its pathogenesis. We further suggest that the exceptions to the latitude gradient (e.g. Japan), which have previously been attributed to genetic factors, may in fact have a dietary basis. Since sunlight also influences the metabolism of fatty acids in the retina, it may also influence the development of retrobulbar optic neuritis-a common antecedent of multiple sclerosis. We suggest a re-examination of the epidemiology of multiple sclerosis based on an understanding of the immunological consequences of illumination of the retina by sunlight.