THE IL-1 RECEPTOR-RELATED T1 ANTIGEN IS EXPRESSED ON IMMATURE AND MATURE MAST-CELLS AND ON FETAL BLOOD MAST-CELL PROGENITORS

Expression of the TI gene, also known as ST2, DER4, and Fit-1, has bee n shown to be associated with cell proliferation. It gives rise to two different mRNAs that encode a receptor-like protein and a soluble mol ecule representing the ectodomain of the receptor Term, Although T1 is a member of the IL-1R family, its biologic function is currently unkn own. In this study, we have analyzed the expression of the T1 surface Ag in murine hemopoietic organs. Mast cells (MCs) were shown to be the only identifiable cell Lineage that expressed T1 at high levels. T1 e xpression was Found on cultured bone marrow-derived immature MCs, Simi larly, freshly isolated connective tissue-type MCs from the i.p. cavit y were also shown to express high levels of T1. Interestingly, the ear liest detectable committed MC precursor isolated from fetal blood (FB) at day 15.5 of gestation, but not circulating hemopoietic stem cells in FB, also expresses high level of T1, Since FB promastocytes lack ex pression of the high affinity IgE receptor (Fc epsilon RI), T1 express ion precedes expression of FceRI in MC ontogeny. The finding that the T1 Ag is selectively expressed at several stages during development of the MC lineage suggests that this cell surface molecule, in combinati on with the well-established markers c-Kit and Fc epsilon RI, should b e valuable for studying the MC lineage.