Production and partial characterization of a monoclonal antibody to rat anterior pituitary somatotrophs.

A cell type-specific monoclonal antibody (Mab) against a cell surface antigen of rat anterior pituitary somatotrophs has been generated by fusion of a nonsecreting mouse myeloma line with spleen cells from a mouse immunized with enzymatically dispersed anterior pituitary cells of adult random cycling female rats. Hybridomas were initially screened for antibodies to cell surface antigens by an enzyme-linked immunosorbant assay using rat anterior pituitary cells and smooth muscle cells of aorta as positive and negative controls, respectively. Positive clones were further checked for cell type specificity by immunofluorescence. Mab WHC-1 is an immunoglobulin M (IgM) with kappa-light chains and is cytotoxic in the presence of complement. Based on double immunofluorescence, this Mab reacted with 22.5 +/- 2.0% (+/- SEM) of the anterior pituitary cells of adult random cycling female rats. Among them, about 93.5 +/- 1.4% were somatotrophs, and only 4.1 +/- 1.2% were mammotrophs. Approximately two thirds of the somatotrophs were Mab WHC-1-positive. The reaction of this Mab with gonadotrophs, thyrotrophs, or corticotrophs were negligible. The percentage of Mab WHC-1-positive cells derived from immunoperoxidase staining was significantly greater than that from immunofluorescence. The cell surface antigen defined by Mab WHC-1 is expressed heavily on GH3 cells, but not on smooth muscle cells. It is resistant to trypsin digestion, but sensitive to ethanol treatment, and exhibits the solubility property of a glycolipid. Mab WHC-1 cross-reacts with the anterior pituitary cell of rabbits, but not mice. These results provide the immunological evidence for heterogeneity among somatotrophs and demonstrate the feasibility of making pituitary cell type-specific Mabs.