Interleukin 5, Human, BioAssay ELISA Kit (IL-5, Interleukin-5, B Cell Differentiation Factor I, T-cell Replacing Factor, TRF)

£943.00 96 Tests

Intended Use:
This Human Interleukin 5 ELISA Kit is to be used for the in vitro quantitative determination of human Interleukin 5 (IL-5) concentrations in serum, plasma, cell culture medium and urine. This kit is intended for research use only and not to be used for diagnostic purposes. It is intended for research use only and is not to be used in diagnostic or therapeutic procedures.

Human IL-5 is a 135 amino acid (aa) polypeptide with a predicted mass of 12.5kD. It is secreted by a restricted number of mesenchymal cell types. In its native state, mature IL-5 is synthesized as a 115aa, highly glycosylated 22kD monomer that forms a 40-50kD disulfide-linked homodimer. Although the content of carbohydrate is high, carbohydrate is not needed for bioactivity. Monomeric IL-5 has no activity; a homodimer is required for function. This is in contrast to the receptor-related cytokines IL-3 and GM-CSF, which exist only as monomers. Just as one IL-3 and GM-CSF monomer binds to one receptor, one IL-5 homodimer is able to engage only one IL-5 receptor. It has been suggested that IL-5 (as a dimer) undergoes a general conformational change after binding to one receptor molecule, and this change precludes binding to a second receptor. Human and mouse mature IL-5 are 71% identical at the aa level. While mouse IL-5 is highly active on human cells, human IL-5 is only marginally active on mouse cells.

Although many cells contribute to inflammation, eosinophils are noted for their contribution to late phase allergic-type disorders. Eosinophils make up less than 10% of the circulation leukocyte population, yet they are known to be extremely important in the inflammatory response to allergic and parasitic agents. When activated within tissues, eosinophils release highly basic preformed mediators such as eosinophil peroxidase and major basic protein. These substances are toxic to parasites and damaging to the surronding tissue, including smooth muscle constriction, increased vascular permeability and superoxide-mediated tissue destruction. While eosinophils have been associated with these inflammatory reactions, the soluble mediators that influence eosinophil availability and function have only recently been identified. Interleukin 5 (IL-5) along with the chemokine eotaxin are key players in the coordination of eosinophil-based inflammatory responses.

The receptor for IL-5 consists of a ligand binding alpha-subunit and a non-ligand binding (common) signal transducing beta-subunit that is shared by the receptors for IL-3 and GM-CSF.

The kinetics of IL-5 binding are still under investigation. Assuming equality with the IL-3 system, (homodimeric) IL-5 binds noncovalently to one IL-5 Ra subunit, which then noncovalently recruits one bc subunit, forming a temporary noncovalently linked trimer. At this point, a second, newly generated IL-5 R complex can be engaged with the IL-5 Ra subunit from complex #1 forming a disulfide bond with bc if complex #2. This is followed by disulfide bonding of the two remaining unlinked receptor components. It is likely that the two bc subunits also become disulfid-linked, creating a functional signal transducing complex, with a stoichiometry of 2/2/2. A newly formed IL-5 R trimer also may link with naturally preformed GM-CSF Ra/bc complexes to form hybrid IL-5 R/GM-CSF R complexes. It is unknown what function these complexes may play in IL-5 activity.

As with many cytokines and growth factors, IL-5 has an approximately 15aa NLS in the body of the molecule. IL-5 with its receptor can be transported into the nucleus following its binding on the cell surface. It is suggested that STATs, which are associated with the receptor, actually enter the receptor via the IL-5 NLS.

Cells known to express IL-5 include eosinophils, NK cells, TC2 CD8+ T cells, mast cells, CD45+ CD4+ T cells, gd T cells and IL-1b activated endothelial cells. IL-5 is best known for its activity on B cells and eosinophils. Relative to cells, IL-5 appears to indue the differentiation of activated conventional B-2 cells (42). In mice, IL-5 promotes production of IgA, IgE and IgG1.

IL-5 appears to perform a number of functions on eosinophils. These include the down modulation of Mac-1, the upregulation of receptors for IgA and IgG, the stimulation of lipid mediator (leukotriene C4 and PAF) secretion and the induction of granule release. IL-5 aslo promotes the growth and differentiation of eosinophils. The exact role that IL-5 plays, however, is unclear; it may act in an adjunct fashion. Finally, there is a great deal of interest in the interaction between IL-5 and the CC chemokine eotaxin. Studies suggest that inflammatory-induced and locally produced IL-5 and eoxtaxin may act on the bone marrow in a cooperative manner.

This IL-5 ELISA is a 3.5 hour solid phase immunoassay readily applicable to measure IL-5 levels in serum, plasma, cell culture medium, and urine in the range of 31.25pg/ml to 1000pg/ml. It showed no crossreactivity with other cytokines tested.


Principle of the Assay:
This IL-5 enzyme linked immunosorbent assay (ELISA) applies a technique called a quantitative sandwich immunoassay. The microtiter plate provided in this kit has been pre-coated with a monoclonal antibody specific to IL-5. Standards or samples are then added to the appropriate microtiter plate wells with a biotin-conjugated monoclonal antibody preparation specific for IL-5 and incubated. IL-5 if present, will bind and become immobilized by the antibody pre-coated on the wells and then be “sandwiched” by biotin conjugate. The microtiter plate wells are thoroughly washed to remove unbound IL-5 and other components of the sample. In order to quantitate the amount of IL-5 present in the sample, Avidin conjugated to Horseradish Peroxidase (HRP) is added to each microplate well and incubated. Avidin is a tetramer containing four identical subunits that each have a high affinity binding site for biotin. The wells are thoroughly washed to remove all unbound HRP-conjugated Avidin and a TMB (3,3’5,5′ tetramethyl-benzidine) substrate solution is added to each well. The enzyme (HRP) and substrate are allowed to react over a short incubation period. Only those wells that contain IL-5, biotin-conjugated antibody, and enzyme-conjugated Avidin will exhibit a change in color. The enzyme-substrate reaction is terminated by the addition of a sulphuric acid solution and the color change is measured spectrophotometrically at a wavelength of 450nm ? 2nm.

Additional information

Kit Components

I8427-04A: IL-5 Microtiter Plate, 1×96 wells
I8427-04B: Biotin Conjugate, 1x7ml
I8427-04C: Avidin Conjugate, 1x14ml
I8427-04D: IL-5 Standard 2×1 vials
I8427-04E: Calibrator Diluent I, 1x22ml
I8427-04F: Calibrator Diluent II, 1x22ml
I8427-04G: Wash Buffer (20X), 1x60ml
I8427-04H: Substrate A, 1x10ml
I8427-04J: Substrate B, 1x10ml
I8427-04K: Stop Solution, 1x14ml, 2N Sulphuric Acid (H2SO4)


Calibrator Diluent I: 7.5pg/ml
Calibrator Diluent II: 6.3pg/ml



Storage and Stability

Store components at 4°C. Stable for 6 months after receipt. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.

Shipping Temperature

On Dry Ice

Source Antigen


Shelf Life

6 Months