KP1 IMMUNOHISTOCHEMICAL DEMONSTRATION OF MACROPHAGES IN COLORECTAL TISSUES - EFFECTS OF DIFFERENT FIXATIVES AND DIFFERENT FIXATION TIMES

The effects of 10 fixatives and formalin fixation time were assessed on the immunoreactivity of KP1 (CD68 antigens) in colorectal tissues in paraffin embedded sections. A panel of fixatives including B5, periodate-lysine-paraformaldehydedichromate, periodate-lysine-paraformaldehyde, 4% paraformaldehyde (PF), zinc formalin, formol dichromate, 10% neutral buffered formalin (NBF), Bouin fluid, Carnoy fluid, and acetone were used to determine an optimal fixative. Another set of colorectal tissues were fixed in 10% NBF progressively at intervals of 1, 2, 4, and 20 hr; 2, 7, and 14 days; and 4 wk to investigate the formalin-induced detrimental effect on CD68 antigens of macrophages. The best result was found after fixation in B5. Short fixation in NBF for 4 hr with trypsinization also gave satisfactory results. There was a distinct decrease in staining intensity after 20 hr exposure to NBF and the reactivities were totally abolished after 2 days. Trypsinization did enhance the staining intensity significantly with no discrimination of fixatives.