A combination immunoblot for the simultaneous detection and differentiation of HIV-1 and HIV-2

A novel tandem repeat cloning technique for creation of multiple short peptide repeats to differentiate closely related antigens

Antibody cross-reactivity is a problem often associated with closely related antigens. This study was aimed to develop a method enabling differentiation of closely related toxins based on antigen designing strategy. The method involves identification of disparate amino acids (AA) confined to target antigen in comparison with two or more closely related antigens, their assembly into a DNA oligomer and further cloning as six tandem repeats (TR) using restriction and ligation strategy into a desired vector and finally generation of antigen specific antibodies. The practical utility of this method was demonstrated by generating and testing the specificity of polyclonal antibodies against staphylococcal enterotoxin C (SEC). Cross-reactivity is a problem often associated with SEC in immunoassays due to its amino acid sequence identity with staphylococcal enterotoxin B (SEB) (40-60%). To circumvent the same, the above-mentioned strategy was applied. Unique AA of SEC (36 AA) in comparison to SEB were selected, reassembled and with deduced corresponding nucleotides, an oligomer of 117 bases was designed. Using primers with restriction overhangs, three constructs were created each with two repeats using a common restriction site. The resulting three constructs were sequentially cloned into alternating restriction sites of pRSET A vector in directional orientation, expressed in E. coli for rTR/SEC protein which was used to generate specific polyclonal antibodies against SEC. Specificity was compared with antibody raised against whole SEC recombinant protein using Western blot and dot blot assays. High specificity was achieved through the developed strategy signifying its possible application to address cross-reactivity problem associated with closely related antigens.

Use of multiple antigenic peptides related to antigenic determinants of infectious bursal disease virus (IBDV) for detection of anti-IBDV-specific antibody in ELISA--quantitative comparison with native antigen for their use in serodiagnosis

Multiple antigenic peptides (MAPs) prepared for the predicted antigenic determinants on the VP2 protein of infectious bursal disease virus (IBDV) were used as antigens in enzyme-linked immunosorbent assay (ELISA)--an alternative to whole viral antigen to detect anti-IBDV antibodies in the chicken sera. Two MAPs were synthesized, which could specifically detect the anti-IBDV antibodies in serum samples by ELISA. The optimum quantity of MAP1 and MAP2 required to coat the wells of the ELISA plate was 5 ng/ml, whereas the amount of purified IBDV whole viral antigen was 500 ng/ml, indicating the high efficiency of MAPs. In this study, we mainly focused on the antigenicity of two eight-branched MAPs to detect anti-IBDV antibodies in ELISA, which would serve as safe, chemically defined, noninfectious alternative antigens to whole virus in serodiagnosis. The specificity and sensitivity of both MAP1 and MAP2 were found to be relatively better than the whole viral antigen.

Comparing tandem repeats and multiple antigenic peptides as the antigens to detect antibodies by enzyme immunoassay

Short synthetic peptides are useful alternatives to whole lysate or recombinant proteins as the antigens used for serodiagnosis of bacterial or viral infections. However, certain known antigenic peptides displayed low seroreactivities in direct enzyme immunoassay. This was believed to be due to the low coating efficiency, a constrained orientation, or loss of flexibility required for optimal antibody binding. Using a model peptide system derived from the V3-loop of HIV-1 gp120, we demonstrated that low antigenicity could be overcome by using either tandem repeats (TR) or multiple antigenic peptides (MAPs) which contained the same amino acid sequence as the monomeric peptide. In our model system, a four-branch MAP was a better choice compared to the tandem repeats because of the MAP's slightly higher sensitivity and lower cost of production.