Non-specific binding of immunoglobulins and protein A-Gold complex with cytoplasmic granules of human mast cells.

A non-specific staining of mast cells by a number of proteins and immunoglobulins has been observed using different immunocytochemical techniques and different antisera at light and electron microscopy level. This finding has been related to an ionic binding of cationic charges, such as aminic groups with an high pI, to the strongly anionic residues of mast cell granules. This hypothesis is supported by the lack of non-specific binding achieved using negatively charged chromogens (i.e. FITC--or Rhodamine-conjugated antibodies) or using cationic dyes before the immunohistochemical reaction. It is therefore stressed that adequate and accurate negative controls must always be carried out in order to get correct interpretations of the staining results.