Kinetics of the Reaction between a Monoclonal IgM Anti-I and Rabbit Red Cells II. Activity of Subunits and Fab′μ-Fragments.

Covalently linked subunits, subunits aggregated from two half subunits, half subunits, F(ab'μ)₂ and Fab'μ were prepared. K-values 1900-5800 times lower than those for intact IgM and rabbit red cells were found for the covalently linked subunits, the aggregated subunits, and F(ab'μ)₂, and 12,500-38,500 times lower for half subunits and F(ab'μ)₂. Only whole subunits and F(ab'μ)₂ agglutinated rabbit red cells; compared to intact IgM the titre was reduced markedly, but from the calculated amount of molecules bound per red cell, IgM was found to be on a weight basis only twice as effective as the subunits and F(ab'μ)₂ in agglutinating the cells. [ABSTRACT FROM AUTHOR]