Nuclear labeling in immunoperoxidase studies of mouse tissue as detected by staining at acid pH

Several peroxidase-Ig conjugates were applied to sections of fixed mouse tissue. When the peroxidase staining reaction was done at pH 4.5 instead of pH 7.4, a striking reaction on nuclear membrane, chromatin, or chromosomes was observed. This staining was prevented by pretreatment of sections with DNase but not with RNase or after acid elution of histones. It is suggested that at acid pH a redistribution and binding DNA of oxidized chromogen or of a chromogen-conjugate complex to DNA may account for the results observed.