ISAC product information

ISAC® is a forward-looking in vitro diagnostic (IVD) application developed for the semi-quantitative analysis of IgE immunoglobulins from human serum. In developing it, the advantages of biochip technology were combined with the methods of immunological diagnosis. ISAC is the first biochip-based allergy test approved for allergy diagnosis according to the regulations of the EU.

The main component of the ISAC biochip is flat glass substrate containing four individual reaction sites (7x7 mm) designed to incubate 20 ul of serum. Each reaction site is enclosed by a hydrophobic Teflon® frame preventing a cross-contamination of samples from different reaction sites. The glass surface is chemically modified to bind allergens in a stable and biologically active manner and each reaction site can contain up to 400 individual allergens.

In contrast to conventional methods ISAC does not employ crude allergen extracts. Rather, ISAC exclusively uses purified natural or recombinant allergen molecules, permitting a better standardization of allergy diagnosis, amongst others. The advantages of using panels of single purified allergen molecules have been demonstrated in a number of peer-reviewed publications.

Each allergen is immobilized in triplicate fashion in each of the four ISAC reaction sites. Therefore, data generated with ISAC are based on a multiple IgE determination in a single assay, providing more reliable diagnostic results in a single analytical step.

For the ISAC® test 20 µl of patient’s serum are applied onto the reaction sites contained in ISAC. IgE antibodies possibly present in the serum of an allergic patient specifically bind only to those areas on the microarray where an allergen has been immobilized. The binding of specific IgE antibodies towards immobilized allergens is detected by adding a fluorescence-labeled anti-human IgE antibody. Subsequently, the fluorescence label is excited with a laser of defined wavelength and the signals generated are collected in a photo detector. This step of the analysis is done fully automated for each reaction site in a process called scanning. The final analysis is software-guided and also fully automated.

 

Incubation of serum takes 2 hours and fluorescence staining an additional hour. Prior to serum incubation as well as in between the individual assay steps a number of washing steps occur. The complete test duration, including preparation, serum incubation and washing is 5 hours. In a standard analytical laboratory, 100 ISAC assays can be performed per day. This equals 8000 individual allergen-specific IgE determinations done on a conventional test system.

The evaluation of the results of ISAC® is computer-guided. The software developed especially for this purpose determines the position of the fluorescence signal relative to the allergen at the respective position in each ISAC reaction site. The software calculates a heterologous calibration curve via a calibration serum tested on one of the four wells. With this curve, all fluorescence intensities are transformed into semi-quantitative IgE concentrations, expressed in kUA/L. These values are then expressed in the form of ISAC® classes (low – moderate – high), which correspond to the well know RAST classes.

For the development of ISAC® only well selected and highly purified recombinant or natural allergens are being used. This makes it possible for the first time to standardize in vitro diagnosis of Type I-related allergies. To date, 103 allergens (ISAC allergen list) are included in ISAC CRD, covering a broad spectrum of different allergies. The test can be used to detect IgE antibodies related to grass- or tree-pollen, animal dander, food, insect venom and mould allergens, amongst others. In selecting the allergens, ISAC is focusing on the major allergens contained in different allergy-producing biological sources. For the selection of key allergens VBC-GENOMICS relies on the opinion of experts in the field of allergology.

For the implementation ISAC assays (ISAC product manual) only standard laboratory equipment is required. In addition, we are providing relevant accessory equipment to our partner laboratories. To scan ISAC biochips, a so-called microarray scanner or biochip reader is required. Today, many hospitals and laboratories have access to this type of equipment as it constitutes a key component of modern life-science, used for the study of gene expression on DNA microarrays. ISAC has been developed and validated using biochip readers developed by CapitalBio (CapitalBio). In particular, we recommend scanners like LuxScan10K. Alternatively, other commercially available scanners can be used. Please, contact our customer care centre for specific questions in this regard.

The world-wide web provides plenty of information about allergic diseases in general. We provide a list of useful references on our link page. Additionally, we recommend exploring www.allergome.org to both specialists and interested patients.