Rapidity of specific antibody-antigen interactions

Analysis of humoral immune responses against viruses has concentrated on studies with serum dilutions, which reflect characteristics pertaining to the diluent buffer but not the serum environment. The majority of virus-specific antibody in serum from foot-and-mouth disease virus (FMDV)-vaccinated cattle bound to antigen within 10-60 s, whereas aspecific reactions evolved more slowly. Upon dilution of sera, the reaction characteristics no longer related to those obtained with the serum, particularly when individual animals were compared. Diagnostic enzyme-linked immunosorbent assay (ELISA) - employing diluted serum - identified little variation in the reactivity of serum samples from different vaccinated cattle. This related to previous analyses showing similar specific antibody titres. In contrast, analyses of serum reactivities over a 10- and 60-s incubation period demonstrated high variation between individual animals. Furthermore, when a challenge infection was performed on vaccinated animals, only those with the higher serum reactivities over a 10- and 60-s incubation were protected. These results demonstrate the importance of the specific serum antibody reactions, which will occur within seconds. Moreover, such qualitative characteristics would be overlooked when employing conventional assays with diluted sera and long incubation periods.