Sera of camelids contain both conventional heterotetrameric antibodies and unique
functional heavy (H)-chain antibodies (HCAbs). The H chain of these homodimeric
antibodies consists of one antigen-binding domain, the VHH, and two constant domains.
HCAbs fail to incorporate light (L) chains owing to the deletion of the first constant domain
and a reshaped surface at the VHH side, which normally associates with L chains in
conventional antibodies. The genetic elements composing HCAbs have been identified, but …