Immunoglobulin M (IgM) 10 Heavy and 10 Light chains 10 Fab and 5 Fc fragments ▣Mol.Wt.~900,000 <10%of serum immunoglobulin. Single Chain(15 kDA) The predominant "early" J-Chain antibody Most primitive immunoglobulin No change in affinity with time Immunoglobulin M (IgM) ◼ 10 Heavy and 10 Light chains ◼ 10 Fab and 5 Fc fragments ◼ Mol. Wt. ~900,000 ◼ <10% of serum immunoglobulin. ◼ Single J Chain (15 kDA) ◼ The predominant "early" antibody ◼ Most primitive immunoglobulin ◼ No change in affinity with time J-Chain