Immunoassays for detecting cytokines: what are they really measuring?

Single cell analyses of cytokine production

Subsets of T lymphocytes have been defined by their secretion of polarized patterns of cytokines. Type 1 and Type 2 subsets have been characterized in a variety of model systems both in vivo and in vitro and are a useful framework for studying immune responses. Recent technical advances have made it possible to analyze cytokine production by these populations at the level of individual cells.

An evaluation of the accuracy of four ELISA methods for measuring natural and recombinant human interferon-g

We describe an evaluation of four ELISA methods, including three commercial kits, for measuring recombinant and natural human interferon-g (hIFN-g). Using a panel of samples, including well-characterized reference standards, we compared relative quantification between assays, within assays and, where possible, the absolute accuracy of quantification as compared to other analytical methods. The four assays generated markedly different results; up to an almost 60-fold difference between the highest and lowest values for one sample. The differences between assays were not necessarily predictable. No single correction factor could be determined to correct results from one method to another across the panel of samples tested. We conclude that investigators should be diligent to revalidate commercial methods before depending on such methods and resultant data.

Alternative assay procedures for cytokines and soluble receptors of the IL-6 family

Human hepatoma cells (HepG2 cells) were transfected with expression vectors for human IL-6 (hIL-6) and rat IL-6R (rIL-6-R). The cell lines were used for testing the biological activity of different IL-6 species, soluble hIL-6R (shIL-6R) and some members of the IL-6 cytokine family by means of an ELISA procedure. The assay is based on induction of the gene expression of the acute phase protein haptoglobin in hepatoma cells and provides an alternative bioassay taking advantage of the hepatocyte stimulatory activity of IL-6 (as opposed to the B9 proliferative assay). A dose-response experiment with IL-6 showed that half-maximal stimulation was achieved with approx. 5 ng/ml of hIL-6 in HepG2 cells and with 5-10 ng/ml muIL-6 in HepG2-rIL-6R cells after 24 h. The same response was achieved with 10 ng/ml shIL-6R in HepG2-IL6 cells. In conclusion, the assay is fast and reliable and might be adopted for other cytokines and receptors with hepatocyte stimulating activity.

ELISPOT for detecting antibody-secreting cells in response to infections and vaccination

Based on immunoassay principles, methods have been developed for the analysis of secreted products at the cellular level. This approach offers substantial methodological advantages compared to traditional immunoassays. In a number of applications cell-based methods have proved able to overcome many of the problems inherent to immunoassays of biological fluids. This review focuses on applications of ELISPOT in natural infections and vaccinations of human individuals. The studies reviewed here have contributed to our understanding of the B-cell responses in infections and the independence of mucosal and systemic immune responses. Whilst diagnostic applications are rare, enzyme immunospot assays have been extensively used in testing the immunogenicity of vaccines. In particular, B-cell responses to mucosal vaccines are better covered with this cellular assay.

Quantitative cell line based bioassays for human cytokines

Research in cytokine biology is ever increasing and it is clear that cytokines are involved in a wide range of pathological and physiological processes. The validity of such research relies heavily on the appropriate measurement of levels of cytokines in various biological samples. Amongst the currently available methods for measuring cytokine levels, it is only the biological assay of samples that can directly provide estimates of biologically active cytokines present in test samples. Of the several bioassay systems available for detecting cytokines, cell line based bioassays are the easiest to perform and provide the most precise and accurate data. The suitability of any cell line for bioassaying a particular cytokine depends on several criteria such as sensitivity, ease of growth maintenance, and cytokine specificity. The design and analysis of cell line bioassays is also important in providing valid estimates of cytokine levels. We review the most useful cell lines currently available for bioassaying cytokines and discuss the design advantages and limitations of cytokine bioassays.