Visualization of immunoreactive growth hormone in cultured peripheral bovine lymphocytes

Growth hormone (GH) has been shown to be released by immune cells in vitro. Thus, the intracellular confinement of GH immunoreactivity was investigated in cultured bovine lymphocytes using con-focal microscopy. Peripheral blood lymphocytes from cows in early pregnancy (10-20 days post insemination; pi) or during mid-pregnancy (day 110-140 pi) were harvested and cultured for 48 h in presence of phytohemagglutinin-M (PHA-M) or served as controls. Thereafter, immunocytochemistry was conducted using a homologous GH-antibody. Double staining (GH-antibody and directly DYE 549 labeled CD3-antibody) was performed to classify the cells. Con-focal laser scanning was applied verifying the immunofluorescence labeling. Interestingly, the presence of GH immunoreactivity in the cytoplasm, which indicates GH synthesis, was restricted to small cells. Whereas, few T-like cells revealed surface bound GH. Lowest immunoreactivity, concerning the number of the total labeled cells as well as the intensity of labeling was recorded in early pregnancy. Stimulation with PHA-M enhanced total labeled cells in early pregnancy. In contrast, PHA-M had no such effects in mid-pregnancy. The results confirm the specific regulation of synthesis of lymphocytic GH during pregnancy in the cow. The identification of cells producing GH and the elucidation of the mechanisms underlying the expression of GH in larger number of cells during mid-pregnancy than in the early pregnancy need further investigations.