Why Does a Peptide Have to be Crosslinked to Another Protein? Synthetic peptides used for antibody production are typically too small to have all of the necessary information to induce the immune system to properly process them and in turn produce high titers antibodies. Numerous techniques have been developed to utilize synthetic peptides but to overcome the above limitations. Some companies utilize MAP (multiple antigen peptide) technology, which allows the juxtaposition of 4 or 8 peptide molecules on a crosslinked lysine core. The MAP technology, developed by Dr. James Tam, results in the production of antibodies to the peptides, but in its simplest form, that used by companies offering custom antibody production, seems to have a low incidence of antibodies produced that can recognize the native protein in situ. Dr Tam, in fact has more recently developed a highly complex combination of lipid and multiple peptide copies that seems to overcome these limitations. The costs of using the latter system are not justified given the high degree of success using synthetic peptides conjugated to various immunogenic proteins. The most commonly used of these carrier proteins is KLH, keyhole limpet hemocyanin, a very large and very immunogenic protein that has been shown over many years to aid in the production of high titer polyclonal antibodies. The primary sequence of KLH, with numerous exposed lysine residues, allows for the covalent attachment of large numbers of peptide molecules. The resultant complex is able to stimulate the immune system to produce antibodies against both the synthetic target peptide as well as KLH itself. Thus it is also important that ELISA analysis be performed using synthetic peptide conjugated to a different carrier protein, typically BSA. Finally, these is some evidence that antibodies can also be produced that react to the crosslinked reagent used to couple the peptide to KLH, and thus at 21st Century Biochemicals, we also utilize a different chemical crosslinker for the attachment of peptide molecules to BSA than was used for coupling peptide to KLH. In this way, ELISA can more accurately measure the presence of antibodies in serum specific for the target peptide.