Human alpha 2-macroglobulin as a cytokine-binding plasma protein. A study with rh-interleukin-1 beta and rh-interleukin-6

Regulation of ADAMTS Proteases

A disintegrin and metalloprotease with thrombospondin type I motifs (ADAMTS) proteases are secreted metalloproteinases that play key roles in the formation, homeostasis and remodeling of the extracellular matrix (ECM). The substrate spectrum of ADAMTS proteases can range from individual ECM proteins to entire families of ECM proteins, such as the hyalectans. ADAMTS-mediated substrate cleavage is required for the formation, remodeling and physiological adaptation of the ECM to the needs of individual tissues and organ systems. However, ADAMTS proteases can also be involved in the destruction of tissues, resulting in pathologies such as arthritis. Specifically, ADAMTS4 and ADAMTS5 contribute to irreparable cartilage erosion by degrading aggrecan, which is a major constituent of cartilage. Arthritic joint damage is a major contributor to musculoskeletal morbidity and the most frequent clinical indication for total joint arthroplasty. Due to the high sequence homology of ADAMTS proteases in their catalytically active site, it remains a formidable challenge to design ADAMTS isotype-specific inhibitors that selectively inhibit ADAMTS proteases responsible for tissue destruction without affecting the beneficial functions of other ADAMTS proteases. In vivo, proteolytic activity of ADAMTS proteases is regulated on the transcriptional and posttranslational level. Here, we review the current knowledge of mechanisms that regulate ADAMTS protease activity in tissues including factors that induce ADAMTS gene expression, consequences of posttranslational modifications such as furin processing, the role of endogenous inhibitors and pharmacological approaches to limit ADAMTS protease activity in tissues, which almost exclusively focus on inhibiting the aggrecanase activity of ADAMTS4 and ADAMTS5.

The inhibitory effect of IL-1 beta on IL-6-induced alpha 2-macroglobulin expression is due to activation of NF-kappa B

The cross-talk between the signal transduction of simultaneous acting cytokines largely determines the final impact of cytokines on their target genes. Both NF-kappaB and STAT3 are transcription factors well known to be activated by many stimuli and to mediate transcriptional activation by binding to specific enhancer sequences. In this study, it is analyzed how IL-1beta inhibits IL-6-induced transcriptional activation of the alpha(2)-macroglobulin promoter. It is shown that IL-1beta prevents STAT3 binding to the two STAT3-responsive sites within the alpha(2)-macroglobulin promoter by association of IL-1beta-activated NF-kappaB to this region. The observation that inhibition of IL-6-induced transcriptional activation of this promoter by IL-1beta is reversed by cotransfection with I-kappaBalpha provides evidence that NF-kappaB activation by IL-1beta is responsible for inhibition of IL-6-mediated trans activation of the alpha(2)-macroglobulin gene. Accordingly, cotransfection of the NF-kappaB subunits p50 or p65 themselves inhibited activation of the alpha(2)-macroglobulin promoter by IL-6. Introduction of point mutations in each of the two NF-kappaB sites overlapping the two STAT3 binding sites within the alpha(2)-macroglobulin promoter provides evidence that each of these two sites counteracts transcriptional activation via STAT3. Most interestingly, at least one functional NF-kappaB consensus site is essential for the IL-6-induced transcriptional activation of the alpha(2)-macroglobulin promoter. Additional data are provided indicating that the activation of NF-kappaB by IL-1beta is also responsible for the inhibition of other IL-6-inducible genes, such as the alpha(1)-antichymotrypsin gene as well as the suppressor of cytokine signaling 3 gene, suggesting a more general relevance of this mechanism for transcriptional regulation.

Trypanosoma cruzi: acute infection affects expression of alpha-2-macroglobulin and A2MR/LRP receptor differently in C3H and C57BL/6 mice

Although a complete cellular and humoral immune response is elicited in Chagas' disease, recent data suggest that other natural elements of innate immunity may also contribute to the initial host primary defense. alpha-Macroglobulins are a family of plasma proteinase inhibitors that are acute-phase reactants in Trypanosoma cruzi-infected mice and humans. Mice contain a tetrameric alpha-2-macroglobulin (MAM) and a monomeric murinoglobulin (MUG). Heterogeneity in their reactions was observed in murine T. cruzi-infected plasma A2M levels despite an overall increase. In addition, up-regulation of the A2M receptor (A2MR/LRP) was observed in peritoneal macrophages during T. cruzi infection. Here, we show that during T. cruzi infection (Y strain), the MAM and MUG hepatic mRNA levels and the corresponding plasma protein levels were up-regulated in C3H and C57BL/6 (B6) mice, but with different kinetics. On the contrary, A2MR/LRP mRNA levels increased in acutely infected C3H mice, but decreased in B6 mice, in both liver and heart. Immunocytochemistry of infected B6 heart cryosections confirmed a less intense endothelium labeling by the fluoresceinated ligand for A2MR/LRP. On the other hand, infected B6 spleen cells displayed higher F-A2M-FITC binding and MAC1 expression, confirming higher A2MR/LRP expression in macrophages. In uninfected mice, as well as after T. cruzi infection, higher A2M plasma levels were measured in C3H mice than in B6 mice. The lower tissue T. cruzi parasitism found in C3H-infected mice could reflect an inhibitory effect of A2M on parasite invasion. Our present data further contribute to clarifying aspects of the role of A2MR/LRP in a model of acute Chagas' disease in different mouse strains.

Measurement of cytokines in clinical samples using immunoassays: problems and pitfalls

With the explosion in interest in cytokines and an increasing understanding of their possible involvement in the pathogenesis of many diseases, the number of studies measuring cytokines in body fluids has increased markedly over the last 5 to 10 years. However, it is readily apparent from the literature that the level of awareness of the many factors that can potentially influence the results obtained is very low. Such factors are likely to contribute considerably to the disparities seen among similar types of study. These include assay properties such as standardization and specificity, type of sample and sample handling, and many biological influences such as age, sex, ethnic background, and diurnal rhythmicity. Clearly, it is not possible to control for all these factors, but a minimum evaluation of assays should be carried out as described, including recovery and parallelity studies using relevant samples and the establishment of reproducibility and normal healthy population levels. An awareness of these factors, which is the purpose of this review, may hopefully lead to an improvement in the quality of studies incorporating the measurement of cytokines in clinical samples and should aid in the interpretation of the data.

Quantitative analysis of T helper 1, T helper 2, and inflammatory cytokine expression in patients after allogeneic bone marrow transplantation: relationship with the occurrence of acute graft-versus-host disease

BACKGROUND

To further delineate the cytokine involvement in human acute graft-versus-host disease (GVHD), we analyzed cytokine expression in peripheral blood mononuclear cells (PBMC) from patients who developed acute GVHD after allogeneic bone marrow transplantation and from those who did not.

METHODS

We used a highly quantitative and sensitive polymerase chain reaction assay based on the coamplification of an internal standard, with the cDNA derived from the mRNA of interest. Results are expressed in copy numbers, after normalization to a fixed amount of actin, allowing comparison between different samples. After a myeloablative regimen, 22 patients with hematological diseases received an unmanipulated allograft from a matched sibling. They were subsequently submitted to prophylactic immunosuppression. We examined the transcription of genes encoding cytokines in PBMC and skin biopsies. We selected T helper 1 (interferon ([IFN]gamma, interleukin [IL]-2), T helper 2 (IL-4, IL-10), and inflammatory (IL-1, IL-6) cytokines.

RESULTS

Four weeks after bone marrow transplantation, the bulk of the PBMC population exhibited an increased expression of IL-1 and IL-6, with no major difference between GVHD+ and GVHD- patients. In addition, although IL-2 expression was not detected, increased levels of IFNgamma mRNA were observed in allografted patients, with higher levels in GVHD+ patients. In skin biopsies sampled at the beginning of GVHD, although low expression of IL-1 and IL-6 could be observed, neither type 1 (IL-2, IFNgamma) nor type 2 (IL-4, IL-10) cytokines could be detected.

CONCLUSIONS

These studies suggest that the occurrence of human GVHD does not seem to be clearly associated with a T helper 1-type cytokine pattern.