The assessment of antibody affinity distribution by thiocyanate elution: a simple dose-response approach.

We describe a simple dose-response approach to assess the affinity distribution of polyclonal antibodies. The proportion of antigen-specific antibodies dissociated by increasing concentrations of the mild chaotropic agent ammonium thiocyanate (NH4SCN) was measured by enzyme immunoassay, and the distribution of tolerances to this agent was presented in a histogram form. Such 'tolerance distribution', which is analogous to that described in classical dose-response bioassays, is proposed as a representation of the actual antibody affinity distribution. To test this approach, we assessed affinity maturation patterns of anti-Plasmodium falciparum IgG antibodies in paired sera obtained from 22 malaria patients during the acute infection and convalescence. We obtained patterns of antibody affinity distributions consistent with those previously described in immunization experiments with the aid of more complex laboratory and computational approaches. Therefore, we suggest the thiocyanate elution technique as an alternative method for rapid assessment of affinity distributions of polyclonal antibodies elicited against complex antigens, readily applicable to large number of serum samples.