Different types of precipitating antibodies in early and late porcine anti-dinitrophenyl sera

Abstract

The anti-dinitrophenyl antibodies produced in pigs at early and late phases of immune response show striking differences when interacting with multivalent antigens. While the early antibody is capable of precipitating hapten-protein conjugates in a very broad range of antigen concentrations, the late antibody precipitates only in a narrow zone of antibody excess. The precipitability of the late antibody is more sensitive to antiserum dilution and to heat treatment than the precipitability of the early antibody. Both antibodies have a sedimentation coefficient 6·7 S and behave as antigenically identical in immunodiffusion. An evidence of certain structural differences between the early and late antibodies is obtained from the patterns of radioactively alkylated peptides containing inter-chain half-cystine residues of the heavy chains. The contrasting character of antigen precipitation can hardly be explained assuming that an increased association constant is the only difference between early and late antibodies. A possibility is suggested that the early and late antibodies represent closely related subclasses of porcine IgG differing by the shape and/or flexibility of the molecule.