ABSTRACT
Shark immunoglobulin heavy chains do not always heterodimerize with light chains, but when they do four isotypes are available. In addition to IgLλ and IgLκ, sharks have IgLσ and IgLσ-cart. The IgLλ loci of sharks are always germline-joined, which may shed light on the origins of the V(D)J rearrangement.
