Human thymic epithelial cells express functional HLA-DP molecules

Human retinal pigment epithelial cells inhibit proliferation and IL2R expression of activated T cells

The purpose of this study was to characterize the effects of human retinal pigment epithelial (RPE) cells on activated T cells. Activated T cells were cocultured with adult and foetal human RPE cells whereafter apoptosis and proliferation were determined by flow cytometry and (3)H-Thymidine incorporation assay, respectively. T cells and RPE cells were cultured directly together or in a transwell system for determination of the effect of cell contact. The importance of cell surface molecules was examined by application of a panel of blocking antibodies (CD2, CD18, CD40, CD40L, CD54, CD58) in addition to use of TCR negative T cell lines. The expression of IL2R-alpha -beta and -gamma chains of activated T cells was analysed by flow cytometry after incubation of T cells alone or with RPE cells. Human RPE cells were found to inhibit the proliferation of activated T cells by a cell contact-dependent mechanism. The RPE cells inhibitory abilities were not affected by blocking of any of the tested surface molecules. The inhibition of the T cells' proliferation correlates with a decreased expression of IL2R-beta and -gamma chains. The T cells regain their ability to proliferate and increase their IL2R-beta and -gamma chain expression within 24 hr after removal from the coculture. It is concluded that the cultured human adult and foetal RPE cells inhibit the proliferation of activated T cells by a process that does not involve apoptosis. It depends on cell contact but the involved surface molecules were not revealed. The proliferation inhibition correlates with a modulation of the T cells' expression of IL2R, and is reversible.

Differential surface expression of HLA-DRB1 and HLA-DRB4 among peripheral blood cells of DR4 positive individuals

Increasing interest in the functional consequences of differential expression of MHC class II molecules prompted us to examine the surface expression of HLA class II molecules on fresh peripheral blood mononuclear cells. Differential regulation of DR4 and DRB4 was shown for peripheral blood monocytes. In addition, DR4 expression is upregulated on B cells of patients suffering from chronic inflammation and is reduced under prednisolone-treatment. The expression levels of total DR molecules on a given cell type are almost identical comparing different haplotypes among non-RA controls, suggesting that the alpha-chain determines the level of surface expression. The present findings fit the hypothesis that the differential expression of HLA class II molecules is involved in regulation of the immune response and may thus contribute to determining susceptibility to immunological diseases.

Comprehensive HLA-DP typing using polymerase chain reaction with sequence-specific primers and 95 sequence-specific primer mixes

HLA-DP is the third of the class II molecules. Its role is antigen presentation, and it has been suggested to play a part in the susceptibility to certain diseases such as berylliosis, sarcoidosis and juvenile chronic arthritis. The standard typing method is SSO typing, although other methods have been used. Probably the best is sequence-based typing, but this is time-consuming and requires expensive equipment. We describe a method for comprehensive HLA-DPB1 and HLA-DPA1 typing using sequence-specific primers. This method has the advantages that it is rapid - typing a single DNA sample takes under 3 hours - and does not require any special equipment or reagents. The method has been shown to be highly accurate by typing 60 cell line DNA samples in which there was 100% agreement between the types obtained and the published information. Similarly typing of 20 DNA samples previously typed by sequence-based typing gave 100% concordance. We used the method to type DNA samples from 102 UK Caucasoid kidney donors. The allele frequencies agree with previously published data. Linkage disequilibria between HLA-DPB1, HLA-DPA1 and the other class II antigens have been investigated. Strong linkage disequilibria exist between certain HLA-DPB1 and HLA-DPA1 alleles. This is unsurprising in view of their proximity on the chromosome. More unexpectedly, the data also suggest that genes further away along the chromosome are in linkage disequilibrium with HLA-DP, forming extended haplotypes.