IMMUNOHISTOCHEMISTRY OF INDIVIDUAL ADENOHYPOPHYSIAL CELLS

ABSTRACT Immunohistochemistry is the intracellular detection of antigens by the use of specific antibodies labelled with a tracer. The choice of the tracer is such that the sites of the antigen-antibody reactions can be visualized by microscopic examination. The present report refers to the human pituitary where most of the immunohistochemical identifications of adenohypophysial cells were conducted with antibodies specific of their hormonal content and labelled with fluorescein isothiocyanate as tracer. Such immunohistochemical identifications had to be correlated to the morphological nomenclatures of the glandular cells based on histochemical stainings. Confusion has been introduced in these nomenclatures by the definition of three to eight cell types using different criteria and different terminologies. In the present report, owing to this absence of standardization, the comparative evaluation of immunohistochemical data have been based on Romeis (1940) and Pearse & van Noorden (1963) nomenclatures. There is strong experimental evidence supporting the localization of adrenocorticotrophic hormone (ACTH) in the basophils of Romeis β type (R-mucoids of Pearse). Somatotrophic hormone (STH) has been consistently found in the acidophils of Romeis a type. In the human, there is no direct evidence to support the localization of prolactin (LTH) in the acidophils of Romeis ε type. Luteinizing hormone (LH) and follicle stimulating hormone (FSH) have both been located in the basophils of Romeis δ type (S-mucoids of Pearse). Further investigations into the human and also into other mammalian species are required to determine if the gonadotrophic hormones have different localizations on the cellular or on the subcellular level. The immunohistochemical localizations of thyroid stimulating hormone (TSH) and melanocyte stimulating hormone (MSH) have not been convincingly achieved. The conclusions drawn from immunohistochemical studies of the adenohypophysis are essentially limited by the cross reactions existing between STH and prolactin, between ACTH and MSH and between LH, FSH and TSH. More experimental data on these immunological cross reactions are still required before more accurate morphological discriminations can be achieved between the cell types secreting STH and prolactin, between those secreting ACTH and MSH and between those secreting LH, FSH and TSH. In addition, when hormones of the adenohypophysis are chemically and/or antigenically closely related, the cells responsible for their secretion are morphologically very similar too. Finally, immunohistochemical studies revealed the lack of species specificity of the pituitary hormones. Extensive cross reactions have been shown between human STH and STH of all mammalian species studied so far. Consistent cross reactions were also found between human gonadotrophins and those of several mammalian species.