The specificity stated for each antibody describes the reactivity of the antibody within the species.
For example, an antibody raised against a human IgG (H+L) immunogen will react with all human immunoglobulins but no other human serum proteins. However it may react with immunoglobulins from other species due to the homology of the target antigen between species.
The immunogen may be a native protein purified from tissue or fluid from the relevant species, or a recombinant protein.
A number of antisera have been raised against multiantigenic peptides. A multiantigenic peptide is composed of a number of copies of chemically synthesised peptides which are attached to a non-immunogenic, branched lysine core. This structure is large enough to elicit an immune response without the need for conjugation to a carrier protein prior to immunisation of the host. The resultant polyclonal antisera are of high avidity with a degree of specificity normally only associated with monoclonal antibodies.
Immunogens are specified multiantigenic peptides and immunoglobulins to ensure that the specificity of the antibody is clear.