Real-time recording of antigen-antibody reactions at surfaces: interpretation of data and a statistical model

Microfluidic processor allows rapid HER2 immunohistochemistry of breast carcinomas and significantly reduces ambiguous (2+) read-outs

Biomarker analysis is playing an essential role in cancer diagnosis, prognosis, and prediction. Quantitative assessment of immunohistochemical biomarker expression on tumor tissues is of clinical relevance when deciding targeted treatments for cancer patients. Here, we report a microfluidic tissue processor that permits accurate quantification of the expression of biomarkers on tissue sections, enabled by the ultra-rapid and uniform fluidic exchange of the device. An important clinical biomarker for invasive breast cancer is human epidermal growth factor receptor 2 [(HER2), also known as neu], a transmembrane tyrosine kinase that connotes adverse prognostic information for the patients concerned and serves as a target for personalized treatment using the humanized antibody trastuzumab. Unfortunately, when using state-of-the-art methods, the intensity of an immunohistochemical signal is not proportional to the extent of biomarker expression, causing ambiguous outcomes. Using our device, we performed tests on 76 invasive breast carcinoma cases expressing various levels of HER2. We eliminated more than 90% of the ambiguous results (n = 27), correctly assigning cases to the amplification status as assessed by in situ hybridization controls, whereas the concordance for HER2-negative (n = 31) and -positive (n = 18) cases was 100%. Our results demonstrate the clinical potential of microfluidics for accurate biomarker expression analysis. We anticipate our technique will be a diagnostic tool that will provide better and more reliable data, onto which future treatment regimes can be based.

Modelling the kinetics of antigen-antibody reactions at particle enhanced optical immunoassays

Functionalized latexes coated by antibodies are used in diagnostic tests for the detection of antigens in biological fluids. A simple kinetic model is presented which is related to the optical monitoring of the formation of specific complexes between antigen and antibody amplified by latex beads. The antibodies are chemically coupled onto chloromethylstyrene (CMST) particles. The kinetic model is able to describe the immunoprecipitin curves of immunolatex beads. The number of fitting parameters is relatively reduced (only three), and the meaning of these parameters can be interpreted in terms of the chemical equilibrium constant, the percentage of active IgG on the latex beads, and optical response. The model explains very well the optical response of immunolatex prepared by covalent coupling of antibodies on polymer carriers.

Attractive adsorbate interaction in biological surface reactions

Recent studies on ferritin adsorption have revealed strong adsorbate interactions during adsorption (H. Nygren, Biophys. J., 65 (1993) 1508). In the present study, efforts were made to quantify the attractive lateral adsorbate interaction and to describe the effect of such interactions on the time- and concentration dependence of biological surface reactions. Attractive forces between ligands increase the time that they are considered neighbours to other ligands. Thus, the inter-ligand interaction effects their distribution and this can be measured experimentally by the pair correlation function g(r). The attractive lateral interaction was shown to affect the surface adsorption of ferritin, virus particles and bacteria, but played a minor role in the binding of antibodies to surface-immobilised antigen.