Unless otherwise mentioned on the product information sheet, all of our products are formulated in such a manner that the lyophilized proteins are very stable at room temperature. However, we recommend that for short-term storage (up to one month) they are best stored at 4°C. For longer periods, we recommend storing the lyophilized products at -20°C. We do not recommend storage at temperatures below -50°C.

For reconstituted solutions of most products, we recommend short-term storage at 4°C. For longer term storage the protein solution should first be aliquoted (to avoid more than one freeze/thaw cycle) and stored frozen at -20°C. Please keep in mind that every freeze/thaw cycle may cause some denaturation of the protein.

RELIATech products are not always formulated with carrier protein or other additives (e.g., BSA, HSA, sucrose, etc.) and are often lyophilized with a minimum amount of salt. As a result, the small amounts of protein can be deposited on the vial during lyophilization as a thin and, sometimes, invisible film. Before opening, we recommend centrifuging each vial in a microcentrifuge for 20-30 seconds to drive any protein that may be lodged in the cap or on the side to the bottom of the vial. Our quality control procedures assure that each vial contains the correct amount of product.

The ED50 is defined as the cytokine concentration at which the activity is 50% of the maximum response. This method of expressing potency should only be used for cytokines whose dose-response curves are sigmoidal in shape. The formula for converting the activity as an ED50 in ng/ml to specific activity in units/mg is:

With a few exceptions, most human cytokines are active on mouse cells. Many mouse cytokines are active on human cells, but may show lower specific activity than the corresponding human cytokine. A few human cytokines, such as IL-7, even exhibit higher specific activities on mouse cells than do the corresponding mouse cytokines. The interferons, GM-CSF, IL-3, and IL-4 are known to be species-specific with very little, if any, activity on non-homologous cells. In contrast, the FGF's and neurotrophins are very highly conserved and show excellent activity on cells of other animal species.

Unless otherwise stated on the data sheet, RELIATech's cytokines are formulated to be reconstituted in sterile water at 0.1-1 mg/ml. Most of our products are lyophilized from protein solutions without buffers and salts. However, a few cytokines have specific salt or pH requirements and these products are lyophilized from an appropriate formulation so that addition of water to the lyophilized protein restores these conditions. Additionally, the solubility of a few products is improved if they are dissolved in solutions of a specific composition. It is extremely important to follow the reconstitution instructions described on the product data sheet to ensure proper formulation of the cytokine. Once a cytokine solution has been prepared according to the recommendations, the user can make further dilutions into buffers appropriate to the particular biological application. Certain additives in solutions used for reconstitution may adversely affect the solubility and bioactivity of cytokines and should be tested in small scale before use.

Several growth factor families consists of so-called homodimeric and/or heterodimeric proteins, containing clusters of disulfid chains. Examples are the TGF-beta? and the PDGF/VEGF family of growth factors. If produced in E. coli these proteins must be refolded under in vitro conditions to obtain native proteins. Very often these leads to incorrect folded dimers with no or less biological activity. Therefore, higher protein concentrations must be used to obtain the same biological effect. For BMP's this is in the range of 3-5-fold and for VEGF₁₂₁ from E. coli this is often in the range of 5-10- fold. Monomeric proteins from E. coli, yeast and higher cells often have similar potencies, if no post-translational modification is necessary (e.g. IL-3, IL-4, EGF, IGF-1).

Soluble receptors are post-translational modified and contains a lot of disulfide bonds and glycosylation sites. If produced in E. coli these often large proteins show no biological activity.

Soluble receptor proteins contain all structural information necessary to bind and inactivate their corresponding ligands.
They can be used:

1. as highly specific inhibitors to prevent interaction of the ligands to transmembrane receptors. They block the action of growth factors in cell culture assays and in pre-clinical animal experiments
2. to prepare in vitro solid phase binding experiments
3. to establish ligand-receptor-complexes for structural research
4. to prepare or select antibodies binding to cell-surface molecules
5. to establish micro-well based biochemical assay for antagonist screening
6. If compared to blocking antibodies, one given soluble receptor will block all corresponding ligands ( e.g. sVEGFR-1/sFlt-1 will block VEGF-A, VEGF-B and PlGF)

Soluble receptor without "tag"-sequences have an advantage for immunisation protocols or if used for epitope mapping. Soluble receptors including a Fc-tag are perfect for unidirectional binding on micro titre plates (e.g. on protein A coated dished) and if predimerised receptors are necessary for high affinity binding. The key advantage is their use in animal models for blocking the activity of a growth factor. The Fc-tag will stabilise the protein and will therefore increase the half-life in the circulation of the animal. We also offer soluble receptors with a mouse or rat Fc-tag for optimal half-life and tolerance in animal models.

1. RELIDA's will only measure biological active ligands. Proteolytic inactivated, degraded or ligands bound to binding proteins will be not detected. Therefore only the relevant concentration will be determined.
2. RELIDA's can be easily modified that all corresponding ligands of a particular receptor can be measured.
3. RELIDA's are comparable sensitive to sandwich ELISA's and in combination can be used to distinguish between the total and free concentration of a particular growth factor or ligand.
4. RELIDA's are the perfect choice to measure the concentration of an active growth factor, and can therefore replace mitogenic assay, e.g. for quality control
5. RELIDA's can be used for high through-put screens of putative antagonists designed to block the binding of a signal molecule to a cell surface receptor.