Protein L is a cell surface protein, expressed by Peptostreptoccocus magnus, which binds to the variable light
chains of immunoglobulins without interfering with antigen binding. It can be used for purification of mammalian
antibodies of all classes in contrast to the Ig-binding proteins protein A and protein G. Detection of
protein L leakage into antibody preparations is important, since protein L could interfere in immunological
assays and cause adverse reactions in vivo. Here we have developed a sandwich ELISA for detection of protein
L in the presence or absence of mouse IgG utilizing specific chicken IgY antibodies. Protein L does not
react with chicken IgY light chains, and it is therefore possible to make an antigen-specific assay. The assay
can be used to detect protein L at a concentration of 0.3 ng/mL in the presence of IgG.
