Quantification of immunoglobulin g in bovine and caprine milk using a surface plasmon resonance-based immunosensor

Development of a mammalian cell-based ZZ display system for IgG quantification

BACKGROUND

Biological laboratories and companies involved in antibody development need convenient and versatile methods to detect highly active antibodies.

METHODS

To develop a mammalian cell-based ZZ display system for antibody quantification, the eukaryotic ZZ-displayed plasmid was constructed and transfected into CHO cells. After screening by flow cytometric sorting, the stable ZZ display cells were incubated with reference IgG and samples with unknown IgG content for 40 min at 4℃, the relative fluorescence intensity of cells was analyzed and the concentration of IgG was calculated.

RESULTS

By investigating the effects of different display-associated genetic elements, a eukaryotic ZZ-displaying plasmid with the highest display efficiency were constructed. After transfection and screening, almost 100% of the cells were able to display the ZZ peptide (designated CHO-ZZ cells). These stable CHO-ZZ cells were able to capture a variety of IgG, including human, rabbit, donkey and even mouse and goat. CHO-ZZ cells could be used to quantify human IgG in the range of approximately 12.5-1000 ng/mL, and to identify high-yielding engineered monoclonal cell lines.

CONCLUSIONS

We have established a highly efficient CHO-ZZ display system in this study, which enables the quantification of IgG from various species under physiological conditions. This system offers the advantage of eliminating the need for antibody purification and will contribute to antibody development.

Recent advances in analytical strategies and microsystems for food allergen detection

Food allergies are abnormal immune responses that typically occur within short period after exposure of certain allergenic proteins in food or food-related resources. Currently, the means to treat food allergies is not clearly understood, and the only known prevention method is avoiding the consumption of allergen-containing foods. From the viewpoint of analytical methods, the effective detection of food allergens is hindered by the effects of various treatment processes and food matrices on trace amounts of allergens. The aim of this effort is to provide the reader with a clear and concise view of new advances for the detection of food allergens. Therefore, the present review explored the development status of various biosensors for the real-time, on-site detection of food allergens with high selectivity and sensitivity. The review also described the analytical consideration for the quantification of food allergens, and global development trends and the future availability of these technologies.

Calibration-free concentration analysis of protein biomarkers in human serum using surface plasmon resonance

In complex biological samples such as serum, determination of specific and active concentration of target proteins, independent of a calibration curve, will be valuable in many applications. Calibration-free concentration analysis (CFCA) is a surface plasmon resonance (SPR)-based label-free approach, which calculates active concentration of proteins using their known diffusion coefficient and observed changes in binding rates at different flow rates under diffusion-limited conditions. Here, for the first time we demonstrate the application of CFCA for determining protein biomarker abundance, specifically serum amyloid A (SAA), directly in the serum samples of patients suffering from different infectious and non-infectious diseases. The assay involves preparation of appropriate reaction surfaces by immobilizing antibodies on CM5 chips via amine coupling followed by serum sample preparation and injection over activated and reference surfaces at flow-rates of 5 and 100 μL/min. The system was validated in healthy and diseased (infectious and non-infectious) serum samples by quantifying two different proteins: β2-microglobulin (β2M) and SAA. All concentration assays were performed for nearly 100 serum samples, which showed reliable quantification in unattended runs with high accuracy and sensitivity. The method could detect the serum β2M to as low as 13 ng/mL in 1000-fold serum dilution, indicating the possible utility of this approach to detect low abundance protein biomarkers in body fluids. Applying the CFCA approach, significant difference in serum abundance of SAA was identified in diseased subjects as compared to the healthy controls, which correlated well with our previous proteomic investigations. Estimation of SAA concentration for a subset of healthy and diseased sera was also performed using ELISA, and the trend was observed to be similar in both SPR assay and ELISA. The reproducibility of CFCA in various serum samples made the interpretation of assay simple and reliable. This study illustrates a significant step forward in rapid monitoring of several protein markers in serum samples, with utility in biomarker validation and other therapeutic applications.

Quartz crystal microbalance immunosensor for the quantification of immunoglobulin G in bovine milk

The development of precise and sensitive methods for milk analysis remains a challenging task in the milk quality control field. A piezoelectric immunosensor was developed for the real-time quantification of immunoglobulin G (IgG) in bovine milk and colostrum. The sensing surface was designed with rabbit antibovine IgG as the detecting molecule, coupled onto a carboxymethyl dextran-coated gold crystal. Total binding and non-specific binding were measured using a quartz crystal microbalance with dissipation (QCM-D). Conditions of analysis, including ligand immobilization, dilution ratio of milk, salinity, and pH of the dilution buffer were optimized by Doehlert experimental design in order to enhance the detection specificity. The performances of the optimized immunosensor were evaluated. The standard curve was established from QCM-D responses and was linear until an IgG concentration of 2500 ng/mL, with a detection limit of 46 ng/mL. The total assay time is 5 min per sample, including the regeneration step. The intra- and inter-assay variation coefficients were equal to or below 4.7 and 6.1%, respectively. The sensing surface was stable for 100 analyses. This technique was successfully applied to the detection of colostrum addition in milk, with a minimum threshold of 0.1%. This new IgG quantification method is particularly interesting as a cost-effective and time-saving alternative for the dairy analytical laboratories when compared with the existing quantification methods.

Perspectives on immunoglobulins in colostrum and milk

Immunoglobulins form an important component of the immunological activity found in milk and colostrum. They are central to the immunological link that occurs when the mother transfers passive immunity to the offspring. The mechanism of transfer varies among mammalian species. Cattle provide a readily available immune rich colostrum and milk in large quantities, making those secretions important potential sources of immune products that may benefit humans. Immune milk is a term used to describe a range of products of the bovine mammary gland that have been tested against several human diseases. The use of colostrum or milk as a source of immunoglobulins, whether intended for the neonate of the species producing the secretion or for a different species, can be viewed in the context of the types of immunoglobulins in the secretion, the mechanisms by which the immunoglobulins are secreted, and the mechanisms by which the neonate or adult consuming the milk then gains immunological benefit. The stability of immunoglobulins as they undergo processing in the milk, or undergo digestion in the intestine, is an additional consideration for evaluating the value of milk immunoglobulins. This review summarizes the fundamental knowledge of immunoglobulins found in colostrum, milk, and immune milk.

Interface design and multiplexed analysis with surface plasmon resonance (SPR) spectroscopy and SPR imaging

Ever since the advent of surface plasmon resonance (SPR) and SPR imaging (SPRi) in the early 1990s, their use in biomolecular interaction analysis (BIA) has expanded phenomenally. An important research area in SPR sensor development is the design of novel and effective interfaces that allow for the probing of a variety of chemical and biological interactions in a highly selective and sensitive manner. A well-designed and robust interface is a necessity to obtain both accurate and pertinent biological information. This review covers the recent research efforts in this area with a specific focus towards biointerfaces, new materials for SPR biosensing, and novel array designs for SPR imaging. Perspectives on the challenges ahead and next steps for SPR technology are discussed.