Immunocytochemical staining of cytocentrifuge prepared cultured cells: nonspecific staining and its elimination.

In an attempt to localize hormones in cytocentrifuge-prepared cultured cells of small cell carcinoma of the lung (SCCL), various modifications of the immunoperoxidase (PAP) procedure (Sternberger, 1979) were tested. When using glutaraldehyde, formaldehyde, or p-benzoquinone fixation (Pearse & Polak, 1975) and rabbit antibodies in primary or bridging steps of the PAP procedure, nonspecific staining (false positives) could be elicited with the majority of rabbit antibodies tested, but not with antibodies from other animal sources. This problem could be eliminated by fixation of cells either with formalin-acetone (Mason et al., 1975) or, when using antibodies from a source other than rabbit, glutaraldehyde. It was not possible to localize ACTH in DMS-79, a human SCCL line known to produce this hormone. However, calcitonin was localized in the calcitonin-producing SCCL line DMS-53. Failure to localize ACTH in DMS-79 may be due to the lower levels of this hormone in DMS-79, as compared to the levels of calcitonin in DMS-53. This study emphasizes the importance of proper controls before concluding successful localization in a given immunocytochemical preparation of cultured cells.