Nature of non-specific staining

Endogenous enzyme activity is readily recognizable in some cases (e.g. staining of peroxisomes with POase substrates) and can be inhibited specifically (Section 17.3.4.3.2.1). 

A common problem with the indirect covalently labeled enzyme methods is that anti-Ig antibodies often adsorb non-specifically to the tissue, resulting in background staining (i) when long incubation or staining periods are used and, (ii) when the ratio of specifically bound and non-specifically adsorbed antibodies becomes smaller (sparsity of antigens or primary antibodies large excess of anti-Ig antibodies). 

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