Mouseplacental macrophages haveadecreased ability to present antigen

Large numbers ofmacrophages canbefound inananimal's uteroplacental unit. Thishighconcentration of macrophages suggests they mustplay animportant role during placenta development. Togain abetter understanding ofthe fuctional capacity ofplacental macrophages, wehaveob- tained ahighly enriched placenta macrophage culture and havederived several cell lines fromthispopulation. Both placental macrophages andcell lines showcolony-stimulating factor 1-dependent growth, express Fcreceptors, andcan perform Fc-receptor-mediated phagocytosis. Inaddition, they express macrophage markers Mac-1, F4/80, andCD14.Al- though placental macrophages express major histocompatibil- ity complex class U molecules constitutively, theydisplay a decreased ability topresent protein antigens toTcells. Since primary fetal liver macrophages ofthesamegestational stage also showadecreased ability topresent antigens, this phenom- enonmayreflect adevelopmental stage ofmacrophages. Macrophages arefound inthepregnant uterus andplacenta (1, 2). These cells havebeensuggested toplay manyroles during pregnancy including thesynthesis ofmonokines, suchas tumornecrosis factor a(TNF-a) andinterleukin 1(IL-1) (2-4), thesynthesis ofimmunosuppressive factors, andphagocytosis ofdebris andmicrobial invaders (2). Inthemouseplacenta, fetally derived macrophages contribute asignificant portion of labyrinthine mesenchymal cells andcells ofthechorionic villous stroma (2, 5). Macrophages havebeendetected byday 10ofpregnancy withsignificant numbers ofmorphologically matured macrophages, displaying themononuclear-phago- cytic-specific cell surface antigen F4/80byday12(5). Al- though these placental macrophages wereshown tobephago- cytic, other functions remain tobedemonstrated. Animportant immunological function ofmacrophages isto activate T cells byserving asantigen-presenting cells and initiate animmuneresponse (6). Oneprevious report, how- ever, hasshownthat placental macrophages areunable to initiate anefficient immuneresponse against Listeria mono- cytogenes (7). Tostudy theimmunological function ofpla- cental macrophages, we haveobtained ahighly enriched primary placental macrophage population. Inaddition, we haveisolated andcharacterized three macrophage cell lines fromday12and13placentas. Ourstudy shows that placental macrophages atthis stage ofdevelopment, despite expressing class IImolecules, havea diminished ability topresent protein antigens toT-cell hybridomas.