MHC-derived peptides and the CD4+ T-cell repertoire: implications for autoimmune disease

The receptor repertoire of peripheral CD4+ cells is primarily determined by selection processes in the thymus. These result in the positive selection of T cells whose receptors weakly recognize self-peptides restricted by class II self-MHC heterodimers. A majority of such self-peptide partial agonists are likely to be derived from self-MHC molecules. It is suggested that these thymically selected, weakly autoreactive T cells may subsequently be stimulated by peripheral exposure to microbially derived agonists that 'mimic' corresponding self-MHC peptides. In turn, 'molecular mimicry' between microbial agonists and tissue-specific self-peptides may lead to T-cell-mediated autoimmune disease. Hence such disease may reflect 'three-way mimicry' between peptides of respectively target tissue, pathogen and self-MHC (or other self-peptide dominantly presented in the thymus). This hypothesis accounts for the role of MHC haplotype in determining susceptibility to (or protection from) autoimmune disease. Direct evidence is presented in favour of the model as applied to diseases such as rheumatoid arthritis, autoimmune uveitus and autoimmune diabetes. Strong circumstantial evidence, based primarily on sequence similarities, is also presented for other autoimmune diseases. However, it is noted that the statistics of database searches, and the lack of predictable correlation between sequence similarity and T-cell cross-reactivity, require that such evidence be substantiated by further direct experiment.

Expression of messenger RNA of the cardiac isoforms of troponin T and I in myopathic skeletal muscle

In the absence of clinical signs, elevated values of the cardiac isoforms of troponin T (cTnT) and I (cTnI) can be found in the serum samples of some patients with skeletal muscle myopathies; the cause is unclear. We studied the messenger RNA (mRNA) expression of cTnT and cTnI in the skeletal muscles of 24 patients with histologically proven myopathies and in 18 patients in whom a myopathy could be excluded. For cTnT- and cTnI-mRNA determination, we designed specific primer pairs for nested polymerase chain reaction. After amplification, the products were digested with 2 restriction enzymes and visualized. We found cTnT mRNA in 7 skeletal muscle biopsy specimens (6 patients with Duchenne muscular dystrophy, 1 patient with a primary sarcoglycanopathy) and cTnI mRNA in 6 (5 with Duchenne muscular dystrophy, 1 patient with a histologically negative biopsy). The mRNA of the cardiac isoforms, cTnT and cTnI, is expressed in the skeletal muscles of patients with Duchenne muscular dystrophy, but also in some other myopathies. Further studies are needed to show whether the mRNA is translated into the protein, but serum levels of cTnT and cTnI in patients with Duchenne muscular dystrophy would seem to indicate this.

Cardiac troponin T and I in end-stage renal failure

BACKGROUND

In patients suffering from end-stage renal failure, cardiac troponin T (cTnT) and I (cTnI) may be increased in serum without other signs of acute myocardial damage. Whether these increases are specific to myocardial injury or nonspecific is not completely clear.

METHODS

We investigated time courses of cTnT and cTnI over 1 year and the clinical outcome over 2 years in 59 patients with end-stage renal failure undergoing chronic hemodialysis. At the start of the study, we divided the patients into two groups, group 1, without history of cardiac failure, and group 2, with history of cardiac failure, and looked for differences between the groups in later adverse outcome. cTnT was measured using the Enzymun((R)) troponin T assay on an ES 700 analyzer (Roche). cTnI was measured on a Stratus((R)) II analyzer (Dade Behring). Creatinine and blood urea nitrogen were measured on a Vitros((R)) 950 IRC (Ortho).

RESULTS

Dialysis acutely increased cTnT (P: <0.01) and decreased cTnI (P: <0.001) regardless of the dialysis membrane used. Although statistically not significant, cTnT but not cTnI was increased more frequently in group 2 than in group 1, in some cases over the whole study period. Five patients (8.5%) died of cardiac complications within 2 years; all of them had mostly increased cTnT and, in one or more samples, increased cTnI.

CONCLUSIONS

Dialysis alters measured cTnT and cTnI concentrations in serum. In patients suffering from end-stage renal failure, sporadic or persistently increased cTnT and cTnI appear to predict cardiac complications. Because of the effects of the dialysis procedure on troponin values, we recommend that blood be collected before dialysis.

Gas Chromatographic Determination of Total Active Ingredient Content of Karathane Technical and Karathane WD. I. Development of the Method

A new GLC method for the direct determination of the active ingredient in Karathane Technical and Karathane WD is presented. The internal standard (4,6-dinitro-o-cresol) in nitrobenzene solution is added to the sample, or the extract residue in the case of Karathane WD, and the solution is chromatographed on a flame ionization instrument, using an 8’ glass column packed with 3% QF-1 silicone oil on 60–80 mesh Gas Chrom Q. Column temperature is programmed from 100 to 230°C. A working standard of known composition is run in the same manner in series with the sample. The precision of a single determination of the total 2,4- and 2,6-dinitrooctylphenyl crotonate isomers (about 74%) in Karathane Technical and the total dinitrooctylphenols and mononitrooctylphenols (about 6%) is s = 0.5% absolute. Data on the analysis of a limited number of Karathane WD samples show good agreement for the total active ingredient.