Techniques for predicting, detecting and reducing aspecific protein interference in assays involving immunoglobulin single variable domains

An immunoassay method comprising:

• (i) contacting an immunoglobulin single variable domain (ISV), or a polypeptide comprising the ISV, with a monoclonal IgG antibody having a heavy chain comprising the amino acid sequence of SEQ ID NO:
• 35 and a light chain comprising the amino acid sequence of SEQ ID NO:
• 36;
• and
• (ii) determining whether the ISV, or the polypeptide comprising the ISV, is bound by the antibody.

An immunoassay method comprising:

• (i) identifying an antibody that binds to the C-terminal end of a second immunoglobulin single variable domain (ISV), wherein the C-terminal end of the second ISV terminates in the sequence VTVSS (SEQ ID NO:
• 33), and wherein the antibody has been isolated and/or purified from a human sample;
• ii) contacting a first ISV, or a polypeptide comprising the first ISV at the C-terminal end of the polypeptide, with the antibody;
• and
• (iii) determining whether the first ISV, or the polypeptide comprising the first ISV, is bound by the antibody.

An immunoassay method for predicting protein interference or risk thereof comprising:

• (i) identifying an antibody that binds to the C-terminal region of an immunoglobulin single variable domain (ISV), and wherein the antibody has been isolated and/or purified from a human sample;
• (ii) contacting a first immunoglobulin single variable domain (ISV) having a C-terminal region, or a polypeptide comprising the first ISV at its C-terminal end, with the antibody;
• and
• (iii) predicting protein interference or the risk thereof by determining whether the antibody has increased or decreased binding to the first ISV, or the polypeptide comprising the first ISV, relative to the binding of the antibody to a second ISV, or a polypeptide comprising the second ISV, wherein the C-terminal region of the first ISV and the C-terminal region of the second ISV differ.