The plasma cell produces immunoglobulins (or antibodies) as an immune response to an antigen, i.e. non-self agent. An immunoglobulin (Ig) is a glycoprotein with a Y-shape. The basic structure of a monomeric unit of antibody consists of two identical heavy chains and two identical light chains. In each of these chains, there are variable and constant regions. The immunoglobulin heavy chain, in particular, is the large polypeptide subunit. It can be used to classify the various isotypes (or classes) of immunoglobulins. In humans and other mammals, the five classes are: (1) immunoglobulin A (IgA), (2) immunoglobulin D (IgD), (3) immunoglobulin E (IgE), (4) immunoglobulin G (IgG), and (5) immunoglobulin M (IgM).
The immunoglobulin E (IgE) has ε (epsilon)-type of immunoglobulin heavy chain (thus, the acronym E). The light chain of IgE may either be kappa (κ) or lambda (λ). Its molecular formula is ε2 κ2) or ε2λ2. In humans, IgEs are monomers. That means they have only one functional unit of antibody. IgEs are present in serum but only in very low amounts. They are produced and expressed on the surface of plasma cells.
IgEs are associated with type I hypersensitivity. They do so by attaching to mast cells and basophils via the latters' IgE-specific Fc receptors (FcεRs). The binding may occur even before IgE interacts with allergens. When bound with allergen, this triggers the cells to release inflammatory mediators such as histamine. IgEs are also involved in protecting the body against parasites, especially helminths (e.g. nematodes) and protozoans (e.g. Plasmodium falciparum).