TISSUE-SPECIFIC AND ONTOGENIC REGULATION OF LIF PROTEIN-LEVELS DETERMINED BY QUANTITATIVE ENZYME-IMMUNOASSAY

To define the physiological role of leukemia inhibitory factor (LIF), it is essential to localize sites of LIF synthesis in vivo, We generat ed polyclonal antibodies specific for native rat LIF, and developed a two-site immunoassay to detect 10 pg LIF/ml, Using this immunoassay, w e determined LIF content of 18 organs, CNS regions, and ganglia throug hout postnatal development of rats, High levels of LIF protein (1.0-11 .0 ng/g tissue) are present in relatively few-tissues: the uterus at l ate proestrus to estrus and on day 5 of pregnancy, ovary at estrus to early metestrus-1, footpads during early postnatal development and thy mus throughout. Intermediate levels (0.5-1.0 ng) are detected in the g ut, skin, skeletal muscle, pancreas and lung at one or more postnatal ages, Low levels (0.1-0.5 ng) are observed in most other non-nervous a nd nervous tissues. LIF protein levels do not completely correspond to reported LIF mRNA levels.