Summary
To study the role of the mannose receptor in cellular uptake and degradation of tissue-type
plasminogen activator (t-PA), a set of five monoclonal antibodies (Moab) was generated
against the mannose receptor isolated from human placental tissue.
All Moab specifically recognised the 175 kDa mannose receptor in a crude placenta
extract, as shown in Western blot analysis. By use of im- munohistochemistry, we showed
that in human placenta only the Hof- bauer cells (fetal macrophages) express the mannose
receptor. Epitope competition experiments indicated that the Moab bound to at least
two different epitopes on the receptor molecule. Moab 14-3, 14-5, and 15-2, which
are directed against one of these epitopes, strongly inhibited the interaction between
the purified mannose receptor and t-PA. These Moab also inhibited mannose receptor-mediated
degradation of t-PA by cultured human macrophages. The low density lipoprotein receptor-related
protein (LRP) mediated t-PA degradation was not affected by the Moab.
It is concluded that the Moab are useful for studying the expression of the human
mannose receptor in Western blot and in immunohisto-chemistry, and for studying the
interactions between the human mannose receptor and the mannose-containing ligand
t-PA.