Solid phase immobilization of immune complexes

A number of automated systems, e.g. Stratus CS (Dade Behring), IMx (Abbott Laboratories) and COBAS core II (Roche Diagnostics) are now commercially available for quantitation of a large variety of analytes of clinical significance. An 

Despite extensive efforts toward covalent immobilization on the solid phase, surface adsorption is still the most widely used method for immobilization. Most adsorptions are carried out by empirically adjusting conditions to avoid or minimize immunoreactivity loses. Other factors that may affect the success of immobilization include (1) limited surface area availability, (2) nonuniform distributions of the immune complexes on the solid phase (3) the nature of random absorption of the immunoreactive species on the solid surface. 

From a manufacturing standpoint, preparation of the double-antibody immune complex can be very labor intensive. For optimal manufacturability and analytical performance of this system, it is important to have a secondary antibody with a moderate to high affinity so that a mixture of immune complexes of appropriate molecular weights is formed. The molecular size and shape of complexes formed depends on a number of parameters, such as temperature, buffer characteristics, ionic strength and the presence of other solution components such as detergents. These conditions must be carefully controlled or else species of very high molecular weight could be formed due to temperature or buffer interactions. Lot-to-lot variability in the primary and secondary antibody raw materials can also affect the solid phase performance if not properly controlled. 

In order to develop a process that is more robust and free from some of the limitations of the double-antibody concept, various methods have been explored to immobilize the primary antibody onto the solid phase. Covalent immobilization of the immunoreactive species directly on a solid support would have the distinct advantage of overcoming the capacity limitations and the possible molecular changes that can take place before or after immobilization. However, this mode has not been widely utilized due to lack of successful and reproducible methods of covalent attachment. A further complication is the uncontrollable heterogeneity of the solid supports used currently for immobilization. Realizing these limitations, the approach used for Stratus has been to choose a design 

3 A COMMERCIAL EXAMPLE OF DENDRIMER-PROTEIN CONJUGATE-BASED REAGENT TECHNOLOGY 

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