Identification of unacceptable background caused by non-specific protein adsorption to the plastic surface of 96-well immunoassay plates using a standardized enzyme-linked immunosorbent assay procedure.

A standardized enzyme-linked immunosorbent assay (ELISA) was used to examine the capacity of immunoassay plates to prevent non-specific protein binding under blocking conditions. Data from 16 types of 96-well microtitre plate from seven commercial sources, are described. Plates were evaluated with respect to their capacity to adsorb a conjugated antibody in diluent buffer containing non-ionic detergent Tween 20 (0.05%) and skimmed milk proteins (5%). Plates with an absorbance value of > or = 0.05, in not more than one well, were defined as within acceptable limits. Major problems were seen in high binding gamma-irradiated polystyrene plates, from all sources, where only < or = 30% of plates were acceptable. These showed high, randomly distributed, non-specific binding, with some wells showing absorbance values > 2.0. Similar results were obtained when high binding plates were repeatedly gamma-irradiated, and after gamma-irradiation of low binding polystyrene plates. For high binding, non- gamma-irradiated polystyrene plates, approximately 70% of plates were acceptable. Better results (86-100% acceptability) were observed for all low binding polystyrene plates. Only one source in three provided acceptable, low binding, polyvinylchloride plates. This paper confirms a widely held view that non-specific binding to certain plates could be a serious factor in both the development and application of ELISAs. Therefore, the test protocol described is proposed as an additional quality control method for certifying ELISA plates by commercial companies.

Antibody production in packed bed reactors using serum-free and protein-free medium.

The present work demonstrates the utility of packed bed reactors for the production of monoclonal antibody. We present data from a continuous process run for the production of over 100 grams of antibody, using serum-free medium. An additional pilot run also demonstrates the potential for continued antibody production under protein-free conditions, using a standard basal medium.

Use of a rotating wire cage for retention of animal cells in a perfusion fermentor.

Separation of cells within a perfused suspension system is still a problem. We modified the rotating steel wire cage described by other researchers (2) for separation of single cells from suspension. The system was mounted to the stirrer shaft of a circular-loop fermenter. After optimization of fermenter design experimental data showed good separation of cells at useful perfusion rates. Data of a 5 l-prototype show with a mammalian tumor cell line a retention rate of better than 95% at a perfusion rate of D = 0.05. Scaling-up studies show a good scaling-up potential and a wide range of possible applications.

A convenient system for the serial quantitation of viable cells measuring luminescence of ATP.

Measurement of intracellular ATP using luminescence offers an alternative method for the routine determination of viable animal cells in a large number of cultures. Optimal conditions of the new technology are described as is its application in various test systems.