Equine anti-hapten antibody. IX. IgM anti-lactose antibodies.

The immune response to a bacterial vaccine of Streptococcus faecalis (strain N) was characterized in all of the seven horses studied by the sustained production of about 90% IgM anti-lactose antibody over a period of 44 weeks with maximum values of the total antibody ranging from 4 mg/ml of serum to 12 mg/ml of serum. With respect to the binding of a lactose-containing ligand the association constants of the antibodies purified from sera obtained between 5 and 44 weeks fell in the range of 1 times 10-5 M-1 to 2 times 10-5 M-1. Not only was there no significant indication of maturation of a-finity in this period but there was a selective limitation of affinity compared to that of 7S antibodies. It was inferred that the synthesis of IgM antibody involves the selective utilization of V-H and/or V-L genes.