Identity of the light chains from the anti-4-azonaphthalene-1-sulfonate IgG and IgM antibodies from a single rabbit

The light and heavy chains were isolated from the specifically purified IgG and IgM antibodies anti-4-azonaphthalene-1-sulfonate of a single rabbit. The heavy and light chains from each source were mixed in equimolar amounts. The binding of ¹²⁵I-labeled 4-iodonaphthalene-1-sulfonate by each recombinant and control preparation was determined concurrently by equilibrium dialysis. At a free hapten concentration of 14× 10⁻⁶M, the recombinants of the γ chains with the light chains from either the IgG or the IgM bound 0.96–0.99 hapten molecules per unit of 160,000 Daltons. Similarly, either light chain combined with the μ chains to give a recombinant that bound 0.52 hapten molecules per unit of 180,000 Daltons. Thus the light chains from the IgG and from the IgM were equivalent in combining with the heavy chains of either source to yield effective hapten binding activity. The light chains from both sources showed essentially identical disc electrophoresis patterns. These results suggest that the same populations of light chain genes are utilized for the synthesis of IgM and IgG antibodies directed against a single antigenic determinant, at least in the early stages of immunization in individual animals.