Antibodies with a split personality
Spikes on the surface of HIV to which antibodies can bind are sparse. One of nature's solutions is to sometimes produce antibodies that bind tightly to a spike with one arm and grab another structure with the other arm. See Letter p.591
 Most antibodies are highly specific, binding with high affinity to a single foreign antigen. However, an analysis of human immunodeficiency virus (HIV) envelope glycoprotein-specific monoclonal antibodies from infected subjects provides evidence for a surprisingly high degree of polyreactivity. Of 134 different antibodies directed at the gp140 envelope glycoprotein cloned from six patients, 75% were polyreactive, binding with high affinity to one gp140 site and with lower affinity to other sites on the viral surface. Relatively few gp140 glycoprotein spikes are displayed on the surface of HIV, so homotypic bivalent antibody binding is disfavoured and 'heteroligation' may help to improve net antibody affinity in such instances.