Leukocytes from heifers at different ages express insulin and insulin-like growth factor-1 (IGF-1) receptors

The objectives of this study were to investigate if insulin receptors (IR) and insulin-like growth factor-1 receptors (IGF-1R) could be detected on bovine leukocytes using fluorescence antibodies and flowcytometry, and use this method to investigate whether the amount of receptors differed among heifers at different ages. Twenty Danish Holstein heifers in the following three age groups were included in the investigation: (1) heifers aged 25-45 days (n = 8), (2) heifers aged 185-205 days (n = 7), and (3) heifers aged 780-900 days (approximately one month prepartum; n = 5). Antibodies against human IR and IGF-1R were used for indirect immunofluorescence staining of cells, and were found to cross-react with the bovine receptors. IR were found on lymphocytes, monocytes, and neutrophils in all animals, while IGF-1R were found only on monocytes and neutrophils. The percentage of IR+ lymphocytes was almost doubled from stage 1 to 3 (34% versus 57%) and IR expression on lymphocytes and monocytes increased significantly (P<0.01) from 6.80 and 13.60 to 8.24 and 17.50 in heifers aged 185-205 days and heifers aged 780-900 days, respectively. No differences were observed for neutrophil IR or IGF-1R expression. In conclusion, surface IR and IGF-1R can be detected on bovine leukocytes by flowcytometry. Interestingly, the highest numbers of IR were found in heifers one month prepartum. The regulation of IR and IGF-1R expression on bovine leukocytes, and their role in host immunity, needs further investigation.