Stability of hormone receptors with fixation: implications for immunocytochemical localization of receptors

Somatostatin receptor staining in FFPE sections using a ligand derivative dye as an alternative to immunostaining

The confirmation of target expression in tissues is a prerequisite for molecular-targeted therapy. However, difficulties are sometimes associated with the production of appropriate antibodies against receptors. We herein developed a ligand derivative dye for the staining of receptors. The somatostatin receptor (sstr) was selected as the target and FITC-octreotate as the detective agent. We performed a blot analysis to detect sstr in the transfer membrane. The sstr2 recombinant protein or cell lysate from a small cell lung carcinoma cell line (H69) was boiled and loaded onto SDS-PAGE, and the proteins were transferred to a membrane. Even after denaturing processes, FITC-octreotate still bound sstr on the membrane. Furthermore, FITC-octreotate depicted the expression of sstr in formalin-fixed and paraffin-embedded (FFPE) sections, a method that we named ligand derivative staining (LDS). The accuracies of immunostaining and LDS were compared at the points of the detection of sstr using FFPE sections of 30 neuroendocrine tumor specimens. The sensitivity of LDS was 81.8%, while those of immunostaining using anti-sstr2 and sstr5 antibodies were 72.7% and 63.6%, respectively. Thus, LDS appears to be superior to immunostaining. A ligand derivative may be used as a substitute for antibodies, and has the potential to support economical, simple, and accurate detection methods.

Effect of paraformaldehyde fixation on localization and characterization of insulin-like growth factor-I (IGF-I) receptors in the rat brain

In order to design an approach for localizing IGF-I receptors within the intact CNS, the effect of paraformaldehyde (PAF) fixation on receptor binding was examined. Cryostat sections of rat brains, which were perfused with 0 to 10% PAF, were incubated in 125I-IGF-I and assayed for binding under equilibrium conditions. Binding was quantified from 10 brain regions, involving laminae and nuclei from median eminence, thalamus, hippocampus, choroid plexus, pyriform cortex, and cerebral cortex, by computer densitometry of film autoradiographs. The specific binding, saturation curves, Bmax and Ka, ligand specificity, and binding reversibility of IGF-I binding sites were not significantly affected by 1% or 2% PAF. However, 4% PAF elevated IGF-I receptor total binding, nonspecific binding, and Ka, and decreased Bmax, presumably by increasing the number of tissue-receptor interconnections. Only nonspecific 125I-IGF-I binding persisted when 10% PAF was used. These results indicate that tissue perfused with 2% PAF can be used for localizing IGF-I receptors by autoradiographic binding methods.

The localization of prolactin binding sites in human breast tissue

An immunohistochemical method involving the application of purified human prolactin and a specific antiserum to human prolactin, followed by the peroxidase-anti-peroxidase immunoperoxidase technique, has been used to detect prolactin binding in benign and malignant human breast tissue. The use of fresh, frozen material has been found to be essential. Prolactin binding has been shown to be a consistent feature of benign breast tissue but a variation within samples has been noted which is irrespective of hyperplastic changes. Fifty six percent of breast carcinomas gave a positive reaction but heterogeneity of binding has been shown to be a significant feature. A relationship between the presence and extent of prolactin binding and good histological differentiation of the tumours has been noted. It is concluded that immunohistochemistry is a suitable method for the demonstration of prolactin binding sites in human breast tissue and can provide useful information with regard to tumour heterogeneity.

A new hypothalamic substance, and not luteinizing hormone-releasing hormone, is detected immunocytochemically by antibody to luteinizing hormone-releasing hormone

Adjacent paraffin sections of rat hypothalami fixed in Bouin's fluid were treated either with buffer or with luteinizing hormone-releasing hormone (LHRH) before immunocytochemical staining with anti-LHRH. Upon buffer pretreatment, pituitary gonadotrophs were unstained and hypothalamic fibers were stained. Upon LHRH pretreatment, pituitary gonadotrophs were stained (receptor reaction) and hypothalamic fibers were unstained. Extension of washes and use of series of neutralizing antisera between LHRH application and immunocytochemical staining, as well as the absence of inhibiting concentrations of LHRH in the later washes and neutralizing antisera removed from the sections, excluded the possibility that the disappearance of visualization of hypothalamic fibers was due to blockage of anti-LHRH in immunocytochemical staining. The results suggested that LHRH removed from the sections an immunocytochemically stainable but as yet unknown analog of LHRH and replaced it with LHRH, which in turn became lost during subsequent immunocytochemical processing. This idea was confirmed by the isolation by high-pressure liquid chromatography of a peak, distinct from LHRH, upon treatment of hypothalami with LHRH. It is suggested that the new substance may be carrier-held and that this substance, rather than LHRH, is normally detected by immunocytochemistry with anti-LHRH. Added LHRH binds not only to high-affinity pituitary receptors but also to low-affinity hypothalamic carriers.