Antibody and HIV-1 gp120 recognition of CD4 undermines the concept of mimicry between antibodies and receptors
Davis SJ, Schockmel GA, Somoza C, Buck DW, Healey DG, Rieber EP, Reiter C, Williams AF. (1992), Nature. 358, 76-9
It has been proposed that antibodies can mimic the binding of a receptor to its ligand and that anti-idiotype antibodies raised against such antibodies can be used to identify the receptor. A large number of antibodies have been raised against CD4, the receptor on T cells for the envelope glycoprotein gp120 of the human immunodeficiency virus, and the site at which gp120 binds to CD4 has been delineated. It has therefore become possible to contrast the fine specificities of a natural ligand (gp120) and antibodies that interact with the receptor at the same site. Here we report that out of a panel of 225 anti-CD4 antibodies, only one showed fine binding specificity that was broadly like that of gp120, but the evidence was against this being an exact mimic. Thus the data indicate that the production of antibody mimics will occur very rarely or not at all and that the anti-idiotype approach is unlikely to be useful. This contention is supported by a review of the results of attempts to use this approach. Taking strict criteria for success, there is no example for which the anti-idiotype approach has led to the discovery of a previously undescribed receptor or other protein of interest.
Key figure: Relative affinities of human CD4 and human-rat chimaeric CD4 molecules (mutants 2, 6, 7, 8, 9) for gp120 and anti-human CD4 antibodies
METHODS. Mutants were prepared and expressed as described in Table 1 legend. For the gp120-inhibition assays, the wells of Falcon 3911 96-well plates were coated with rabbit anti-mouse IgG at 50 μg ml-1 for 45 min at room temperature and then washed and incubated with tissue culture supernatant containing the anti-gp120 mAb 108 overnight at 4 °C. Plates were then washed and incubated with 100 μI recombinant soluble gp120 at 300 ng ml-1 in tissue culture supernatant (MRC AIDS Directed programme) for 5h at 4°C. After a final wash the plates were incubated with 20-30 μl of 300-320 ng ml-1 human sCD4 labelled to specific activity of 10-15 μCi μg-1 with 125I using the Bolton-Hunter reagent31 (Amersham), together with serial dilutions of unlabelled purified human sCD4 or 5-fold-concentrated tissue culture supernatants containing the soluble human-rat chimaeric proteins at different known concentrations. The antibody inhibition assays were performed in the same manner using antibody at 200 ng ml-1 or at 1/150-300,000 dilutions of ascites in the place of mAb 108 and gp120 and 75-100 ng ml-1 125I-labelled human sCD4 with the various inhibitors. After overnight incubation the plates were washed and the radioactivity bound to the plates determined by gamma counting. The data shown are representative of 4-8 determinations.