Immunochemical analysis of IgG subclasses and IgM in South American camelids

Antibodies are glycoproteins comprising two heavy and two light chains. Surprisingly, all members of the family Camelidae possess a fraction of antibodies devoid of both light chains and the first constant domain (CH1). These kinds of antibodies are known as heavy chain antibodies (HCAbs). There are three subclasses of IgG in dromedaries, namely IgG1, IgG2 and IgG3 of which, IgG2 and IgG3 are of the HCAbs type. In the present work, the different IgG isotypes from guanaco (Lama guanicoe), llama (Lama glama) and vicuna (Vicugna vicugna) were purified and characterized. Interestingly, it was found that IgM was capable of binding to protein A. The different subclasses of immunoglobulins were also assayed for their ability to fix complement. Both IgG1 and the total serum were able to fix complement, whereas IgG2 and IgG3 fixed complement even in the absence of antigen.