The immunoassay of cytokines and growth factors in biological fluids.

There are a number of problems associated with the development of standards suitable for use in the most commonly used assays to detect cytokines in biological fluids. These problems include: (i) the failure of some MoAbs used in immunoassays to detect all different <> of recombinant or natural material; (ii) the use of many different MoAbs, with different specificities, in different immunoassay kits, and (iii) the detection of non-active cytokines (fragments, inhibitors, receptor antagonists, etc.) in these immunoassays. As a result, it is possible to have biologically active material which is not detected in these immunoassays. Alternatively, biologically inactive material can be detected in these assays and is indistinguishable from biologically active material. In addition, the use of different antibodies with different specificities, affinities and avidities in different kits designed to detect the same biological materials results in markedly different sensitivities and specificities. Many of these same concerns can be raised for the use of bioassays for detection of molecules in biological fluids. The solution will not be simple (if possible at all). In most cases, the immunoassay kits are designed to detect <> material in biological fluids, but are made with MoAbs against recombinant material. Because of the markedly different specificities, affinities, etc. of the MoAbs in these kits, their standardization is possible only with a highly purified preparation of natural material. For the assay of recombinant materials, immunoassays should be specifically designed with the recombinant material in mind (i.e. the MoAbs made specifically against the recombinant material to be detected or shown to bind effectively with the recombinant material). Importantly, it should be made clear to investigators using different immunoassays that: (i) the reporting of biological material detected using immunoassays can only be made in units of weight (i.e. ng/ml); (ii) because of the detection of biologically active and inactive material using immunoassay kits these assays cannot be directly compared to bioassays or their results represented as <>; (iii) because of the difference in specificity and sensitivity of the different reagents used in different immunoassays, the results from different assays cannot be directly compared, and (iv) because of these same considerations, comparison of different > of materials within a single immunoassay is also not possible. The use of specific immunoassays for recombinant material in combination with bioassays and the use of cytokine standards, made from highly purified natural material, would help to standardize the results in this field.