Monoclonal antibodies requiring coating buffer with low pH for efficient antigen capture in sandwich ELISA: the rarities or practically important phenomena?

This article reexamines some opinions concerning pH requirements for optimal immobilization of monoclonal antibodies (mAbs) by passive adsorption in antigen capture ELISA. It was discovered that substitution of "classical" sodium phosphate (pH 7.5) and carbonate (pH 9.5) coating solutions by acid (pH 2.8) buffers maximized antigen capture 4 out of 10 different tested anti-HBsAg mAbs, resulting in a 1.5-2.5 increase of binding curve coefficients. By measuring both mAbs amounts and functionality, the enhancement effect was attributed to the better preservation of solid phase antibodies activity.

Western blot analysis of human and rat serotonin transporter in platelets and brain using site-specific antibodies: evidence that transporter undergoes endoproteolytic cleavage.

BACKGROUND: Serotonin transporter (SERT) is important target molecule for many antidepressive drugs and substances of abuse and is implicated in psychiatric disorders. We performed immunoblotting analysis of human and rat SERT in platelets and brain using the panel of eight site-specific SERT monoclonal and polyclonal antibodies (mAbs and pAbs). METHODS: SDS-PAGE/Western blotting was conducted using peroxidase-labeled DEAE and affinity purified SERT antibodies under conditions preventing SERT post-extraction degradation. RESULTS: Immunoreactive polypeptides of 14, 22, 32, 35, 37, 56, 68, and approximately 150-200 kDa were revealed in human platelet extracts using N-terminal and C-terminal SERT antibodies. In rat brain, C-terminal mAbs detected 68, 56, and 37 kDa proteins, in postmortem human brain predominated 35-37 kDa proteins. The immunoreactivity was abolished after antibody preadsorption with antigens. N-terminal pAbs recognized the 68 kDa protein, affinity purified on C-terminal mAbs, confirming its identity as full-size human SERT (the predicted size approximately 70.5 kDa). CONCLUSIONS: The explanation of the results of immunoblotting most likely is a site-specific SERT endoproteolytic cleavage and a marked difference in glycosylation rather than nonspecific protein degradation, cross-reactivity with other epitopes or SERT alternative splicing.

Kinetic analysis of interactions between bispecific monoclonal antibodies and immobilized antigens using a resonant mirror biosensor.

A resonant mirror biosensor (IAsys) protocol is described for the comparative kinetic analysis of the ability of monoclonal antibodies (Mabs) and bispecific antibodies (Babs) to bind immobilized antigens. The protocol has been optimized and validated using the panel of affinity-purified antibodies, including two parental Mabs, one specific to human immunoglobulin G (hIgG) and another specific to horseradish peroxidase (HRP), and a Bab derived thereof by cell fusion (anti-hIgG/HRP Bab). The real-time kinetic analysis of antigen-antibody interactions using this protocol allows to demonstrate the differences in the avidity of bivalently binding Mabs and monovalent Babs. As shown in our previous study [J. Immunol. Methods 261 (2002) 103], the observed equilibrium association constants (Kass) determined by IAsys using this protocol yield figures almost overlapping with those obtained by solid-phase radioimmunoassay (RIA). The described protocol is suited for the investigation of the effects of valency on the binding properties of antibodies. It also may be applied for the selection of Mabs and Babs with desired features, for different fields of application.

Analysis of the binding of bispecific monoclonal antibodies with immobilized antigens (human IgG and horseradish peroxidase) using a resonant mirror biosensor.

The interaction between two monoclonal antibodies (mAbs) and their corresponding bispecific antibody (bAb) with immobilized antigens has been examined using a resonant mirror biosensor (IAsys). BAbs were produced by cell fusion. The analysed panel of affinity-purified antibodies included two parental mAbs, one specific to human IgG (hIgG), and another specific to horseradish peroxidase (HRP), and a bAb derived thereof (anti-hIgG/HRP). The real-time analysis showed the drastic differences in the avidity of bivalent anti-HRP mAbs and anti-HRP shoulder of bAbs. Thus, the observed equilibrium association constant (K(ass)) of anti-HRP mAbs was about 50 times higher that of anti-HRP shoulder of bAbs. The ratio of association rate constants (k(ass)) of mAbs and bAbs was about two, due to the statistical factor of two binding sites per bivalent antibody molecule. However, the dissociation rate constant (k(diss)) of anti-HRP shoulder of bAbs was 21 times higher k(diss) of anti-HRP mAbs. The comparison with the theoretical model shows that these observations are consistent only with a situation in which bivalent binding of mAbs with immobilized HRP predominates over monovalent binding. On the contrary, the second parental mAb (anti-hIgG) did not show the increase in avidity due to bivalent binding, compared to the anti-hIgG shoulder of bAbs, suggesting that this mAb was bound monovalently to immobilized hIgG. The K(ass) values determined by solid-phase radioimmunoassay (RIA) yielded figures almost overlapping with those obtained by IAsys. The results of the comparison of bAbs and mAbs are discussed from the viewpoint of the use of bAbs in heterogeneous systems. On the other hand, these data demonstrate that real-time analysis of antibody binding parameters in IAsys biosensor is valuable for the selection of mAbs and bAbs with desired features, for different fields of application.