The immunoglobulin A isotype of the Arabian camel () preserves the dualistic structure of unconventional single-domain and canonical heavy chains.

Introduction: The evolution of adaptive immunity in resulted in the concurrent expression of classic heterotetrameric and unconventional homodimeric heavy chain-only IgG antibodies. Heavy chain-only IgG bears a single variable domain and lacks the constant heavy (C) γ1 domain required for pairing with the light chain. It has not been reported whether this distinctive feature of IgG is also observed in the IgA isotype.