Rabbit Anti-Human C1q polyclonal antibody for IHC. The C1q complex ispotentially multivalent for attachment to the complement fixation sites ofimmunoglobulin. The sites are on the CH2 domain of IgG and, it is thought, onthe CH4 domain of IgM. The appropriate peptide sequence of the complementfixing site might become exposed following complexing of the immunoglobulin,or the sites might always be available, but might require multiple attachmentby C1q with critical geometry in order to achieve the necessary avidity.