Autoimmune disease development based on possible mislocalization of intracellular and extracellular proteins

BACKGROUND

T helper cells can differentiate into several subsets of T lymphocytes, including Th1, Th2, and regulatory T (T_reg) cells. As a result of this ability to differentiate, the corresponding T cell receptor (TCR) spectra display considerable cellular plasticity and interchangeability. In contrast, T lymphocyte differentiation and separation into CD4⁺ and/or CD8⁺ T cell lines creates stable populations over a person's lifetime, which abrogates the plasticity and interchange between these cell types and their corresponding TCR spectra but results in considerable stability regarding the corresponding TCR sequences and spectra. This separation of TCR spectra agrees with the well-known concept of major histocompatibility complex class (MHC) restriction. Therefore, CD4⁺ and CD8⁺ T cell populations possess different (but stable) TCR spectra, which present differences in antigens between intra- and extracellular space. Thus, mislocalization can lead to autoimmunization and the development of autoimmune disease.

METHODS

To test this hypothesis, human intra- and extracellular proteins and intra- and extracellular extracts were incubated overnight with whole-blood samples from the same subject, and the following day, a cell proliferation assay based on bromodeoxyuridine (BrdU) incorporation was performed.

RESULTS

The BrdU assay showed that the addition of intracellular proteins and extracts to the mixture resulted in significantly greater cell proliferation after overnight incubation, whereas significantly less proliferation was obtained with addition of extracellular proteins and extracts (plasma).

CONCLUSIONS

These results support the proposed hypothesis and show that hidden antigens are present in and released with intracellular proteins. Furthermore, both albumin and insulin activated CD4⁺ and CD8⁺ lymphocytes in a concentration-dependent manner. At low concentrations (<0.1μg/ml), both proteins showed the ability to inhibit CD4⁺ and CD8⁺, whereas at high concentrations (>1000μg/ml), both proteins activated CD4⁺ and CD8⁺ T lymphocytes.

In vitro model for the activation of CD4 and CD8 T cell receptors

Previously, most models that sought to explain the misregulation of immune cell function assumed molecular similarities between the disease-causing pathogens and the host's proteins. In recent time several different models have been proposed and in this study, these concepts are compared to a new hypothesis proposing another explanation for this immune dysregulation: the possibility that the mislocalization of proteins may be responsible for autoimmune activity. Based on this hypothesis, proteins are recognized as self or non-self depending on where they appear in sufficiently high concentrations. To examine this new idea, the intracellular human proteins beta-actin, GAPDH, and hemoglobin as well as the extracellular human proteins insulin and albumin, were added to human whole blood samples. After an incubation period, the activation of whole-blood T lymphocytes in the samples was measured. The observed activation pattern of the T lymphocytes fit well with the proposed hypothesis. Therefore, these data suggest that protein mislocalization and/or errors within protein trafficking might be important in the development of autoimmune diseases.

High sensitivity of free lambda and free kappa light chains for detection of intrathecal immunoglobulin synthesis in cerebrospinal fluid

BACKGROUND

So far, an inflammation of the central nervous system (CNS) is diagnosed by immunoglobulin measurement in cerebrospinal fluid (CSF) and serum as well as by determination of the oligoclonal bands. With the free kappa and lambda light chains, new markers to diagnose intrathecal synthesis are available.

METHODS

In addition to routine diagnostic tests and the assessment of standard parameters, free immunoglobulin light chains were measured in the CSF of patients with neurological disorders.

RESULTS

A significant agreement was found between an increase in free kappa light chain CSF serum quotients and results of the currently widely applied method of oligoclonal band measurement for the detection of intrathecal immunoglobulin synthesis. A sensitivity of 95% and 100% specificity for free kappa light chain concentrations at a cut-off of 0.41 mg/l was determined for free kappa light chains compared with oligoclonal bands. However, the free lambda light chains in 20 out of the 110 investigated samples were characterized by inconsistent behaviour. These otherwise unremarkable samples yielded increased CSF quotients, leading to the assumption that free lambda light chains represent a highly sensitive measure of intrathecal immunologlobulin synthesis. Thirteen of the 20 samples described above were obtained from patients with cerebral infarction, 4 samples derived from patients with cerebral paresis (primarily facial paresis), one sample was from a patient with multisystem atrophy and two were obtained from patients with migraine and neuralgia.

CONCLUSION

These findings suggest that the high sensitivity of lambda light chains for the detection intrathecal immunoglobulin synthesis may be of benefit in establishing clinical diagnoses.

Activation of T-lymphocytes by LDL-cholesterol

Native LDL-cholesterol can be mechanically stressed by strong vortexing. According to one hypothesis, mechanical shear stress within the vessel can lead to an aggregation of LDL-cholesterol and subsequently to activation of CD4 and CD8 T-lymphocytes. The goal of this study was to determine the proportion of activated CD4 and CD8 T-lymphocytes that is induced by adding unstressed and mechanically stressed LDL-cholesterol to whole blood samples. Whole blood was taken from 12 healthy subjects. All probands fasted for at least 12 h before blood withdrawal. In each case, 1 ml of whole blood from each subject was incubated for 16 h at 32 degrees C (89.3 degrees F) with concanavalin A (A), without additive (B), with mechanically stressed LDL-cholesterol (C) or with native LDL-cholesterol (D). Subsequently, the samples were measured by four-color flow cytometry. CD3, CD4, CD8, and CD69 were measured as activity markers. CD69 was plotted against CD4 and CD8, and the proportions of activated CD4 and CD8 T-lymphocytes were determined. Native and vortexed LDL-cholesterol elicited significantly different types of T-cell activation. While native LDL activated CD4 T-cells to only a small extent, mechanically stressed (vortexed) LDL potently activated CD8 T-cells. Purely mechanically-induced changes in LDL-cholesterol may be one mechanism that contributes to the activation of CD8 cells and, as a consequence, the emergence of arteriosclerosis.