NATURALLY-OCCURRING ANTIBODIES DEVOID OF LIGHT-CHAINS

RANDOM association of VL and VH repertoires contributes considerably t o antibody diversity1. The diversity and the affinity are then increas ed by hypermutation in B cells located in germinal centres2. Except in the case of 'heavy chain' disease3, naturally occurring heavy-chain a ntibodies have not been described, although antigen binding has been d emonstrated for separated heavy chains4 or cloned VH domains5. Here we investigate the presence of considerable amounts of IgG-like material of M(r) 100K in the serum of the camel (Camelus dromedarius)6. These molecules are composed of heavy-chain dimers and are devoid of light c hains, but nevertheless have an extensive antigen-binding repertoire, a finding that calls into question the role of light chains in the cam el. Camel heavy-chain IgGs lack CH1, which in one IgG class might be s tructurally replaced by an extended hinge. Heavy-chain IgGs are a feat ure of all camelids. These findings open new perspectives in the engin eering of antibodies.