Amphibian
The Xenopus tropicalis, as a an example of a tetrapod with the idiosyncrasies of an amphibian (western clawed frog) also has 5 classes of Ig. IgM, IgD, IgX and IgY. There are some differences to mammals. The IgD, for instance is not short like the mammalian variant, but is longer and has 8 components. It is likely involved in immune defence since it can be bound by granulocytes through IgD-binding receptors. IgX is an IgA analogue, which means it's used in mucosal defence and is produced much in the organism. The IgY is found in birds, amphibians and reptiles and functions homologously to mammalian IgG. IgY is hence involved in opsonization and coating pathogen surfaces by agglutination. IgF is similar to IgY in sequence, but has…show more content… The Cμ and Cδ are closely linked. Once these rearrange, the Ig genes express themselves as VDJCμCδ mRNA. Through alternative splicing, μ and δ chains are derived. The Cμ has a 4 domain oranization, and each of the 3 codons are encoded by a separate codon. μ is expressed first in a new B cell, with a short cytoplasmic tail and needs other molecules for further signalling. The δ expression is after μ in immature B cells, but it is shut down in activated b cells. So we see that the expression that is related to the maturity of the B cell.
Of the Ig's, δ is the most variable. It is expressed in humans with 2 domains, yet has long mutli-domain in teleost. Most often C regions don't rearrange (Cμ and C8 exception), but they undergo a class-switch in mature B-cell exposed to antigens. Unlike the μ, some downstream isotopes have long cytoplasmic tails and can signal independently: class switching is connected to immunological memory and increased secondary response. We also see here the efficient and elegant nature of isotypes.
Of the mammals, the biggest deviation of the evolutionary direction in tetrapods' Ab is in camelidae. The camelid Ab don't pair with light chains but function as homodimers of heavy