Wat. Slieker et al., ER-MP12 ANTIGEN, A NEW CELL-SURFACE MARKER ON MOUSE BONE-MARROW CELLSWITH THYMUS-REPOPULATING ABILITY .1. INTRATHYMIC REPOPULATING ABILITYOF ER-MP12-POSITIVE BONE-MARROW CELLS, International immunology, 5(9), 1993, pp. 1093-1098
We searched for new cell surface markers that allow a positive identif
ication of thymus-repopulating cells in the bone marrow (BM) of the mo
use. Recently we raised two rat monoclonal antibodies (ER-MP12 and ER-
MP20) that recognize cell surface antigens expressed by mouse haematop
oietic progenitor cells, among which are progenitor cells of the macro
phage lineage. Here we show that the ER-MP12 antigen, but not the ER-M
P20 antigen, is also expressed by BM cells with thymus-repopulating ab
ility. Using ER-MP12 and ER-MP20 in two-colour immunofluorescence anal
ysis six subpopulations of BM cells can be identified. The thymus-repo
pulating ability of each BM subpopulation was assessed after fluoresce
nce-activated cell sorting and subsequent intrathymic injection into s
ublethally irradiated Thy-1 congenic recipient mice. Thymus-repopulati
ng activity appeared to be exclusively confined to two subsets of BM c
ells expressing either high or intermediate levels of the ER-MP12 anti
gen, but lacking ER-MP20 antigen expression. These BM subsets comprise
d 1 - 2% and 30% of total nucleated BM cells respectively. The frequen
cy of thymus-repopulating cells was maximal in the minor BM subpopulat
ion with the highest level of ER-MP12 antigen expression. We conclude
that ER-MP12 detects a hitherto unknown cell surface marker expressed
by BM cells with thymus-repopulating ability.