a polypeptide chain a subunit of an immunoglobulin molecule, of high molecular weight, such as the γ, α, μ, ΄, or ε chains, determining the immunoglobulin class and subclass. This chain also determines whether complement can be bound and whether the chain can pass through the placenta. There are two identical chains in each immunoglobulin.
Synonym(s): H chain
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Examples: glitazone, GI cocktail, etc.