Biotin-protein ratios and stability of biotinylated immunoglobulins as standards for the quantitation of biotin-binding immunoglobulins

The influence of biotinylation on the ability of a computer designed protein to detect B-cells producing anti-HIV-1 2F5 antibodies

Antibodies against the HIV-1 2F5 epitope are known as one of the most powerful and broadly protective anti-HIV antibodies. Therefore, vaccine strategies that include the 2F5 epitope in their formulation require a robust method to detect specific anti-2F5 antibody production by B cells. Towards this goal, we have biotinylated a previously reported computer-designed protein carrying the HIV-1 2F5 epitope aiming the further development of a platform to detect human B-cells expressing anti-2F5 antibodies through flow cytometry. Biophysical and immunological properties of our devised protein were characterized by computer simulation and experimental methods. Biotinylation did not affect folding and improved protein stability and solubility. The biotinylated protein exhibited similar binding affinity trends compared to its unbiotinylated counterpart and was recognized by anti-HIV-1 2F5 antibodies expressed on the surface of patient-derived peripheral blood mononuclear cells. Moreover, we present a high affinity marker for the identification of epitope-specific B cells that can be used to measure the efficacy of vaccine strategies based on the HIV-1 envelope protein.

Isolation and characterization of human neutralizing antibodies to rabies virus derived from a recombinant immune antibody library

A human immune Fab library was constructed using RNAs from peripheral blood lymphocytes obtained from rabies virus hyperimmune volunteers on phagemid vector. The size of the constructed Fab library was 2 x 10(7) Escherichia coli transformants. After four rounds of panning on whole inactivated rabies virus (PV-11), phage clones displaying rabies virus-specific human Fab were selected. The specificity of soluble Fab antibody fragments, derived from positive phage clones was verified by ELISA. Among 20 specific Fab clones, the genetic sequence of 6 of them (FabRV01, FabRV02, FabRV03, FabRV04, FabRV05, and FabRV06) was analyzed. The variable heavy (VH) and variable light (VL) domains were found to share 90% and 93% homology with sequences encoded by the corresponding human germline genes, respectively. The soluble Fab fragments, expressed in Escherichia coli were purified by a single step Nickel-NTA affinity chromatography via a hexa-histidine tag and their binding specificities to rabies virus were confirmed. Three of the Fab antibodies, FabRV01, FabRV02 and FabRV03, showed binding characteristics to rabies virus glycoprotein antigenic site III with affinities in the K(D) range 7 x 10(-9) to 5 x 10(-8)M. The Fab fragments showed dose-dependent neutralization properties for the challenge virus standard (CVS-11).

Quantitation of biotin-binding immunoglobulins G, A, and M in Human Sera Using F(ab')2anti-human immunoglobulin-coated microplates

Biotin-binding IgG (B-IgG) in human sera was quantified using previously developed F(ab')(2)anti-human IgG-coated multiwell microplates (Muratsugu M. et al., 2003, Biol. Pharm. Bull., 26, 1605--1608). The levels of B-IgG in sera, however, were higher than those we predicted. In this study, we modified the assay using F(ab')2anti-human IgG-coated multiwell microplates and successfully quantified the levels of B-IgG in sera. The cause of the unpredicted results was discussed in the text. In addition, the levels of biotin-binding IgA (B-IgA) and IgM (B-IgM) in sera could be measured using F(ab')2anti-human IgA- or IgM-coated multiwell microplates. We quantified B-IgG, B-IgA, and B-IgM in sera from healthy specimens and patients with bronchial asthma, atopic dermatitis, epilepsy, and juvenile rheumatoid arthritis.