Antibody which defines a subset of bone marrow cells that can migrate to thymus.

A T-cell line of immature phenotype, 16C1, has been shown to have specific capacity to migrate to and localize in the thymus of irradiated mice. Several antibodies specific for the Pgp-1 molecule have been tested for their capacity to inhibit the migration of 16C1 and of bone marrow to thymus in just a 3-hr double-label migration assay. Analysis of Pgp-1 expression has revealed that 16C1, derived from C57BL mice, characteristically binds antibodies specific for the Pgp-1.1 and not the Pgp-1.2 allelic determinant, which is normally expressed by cells from C57BL mice. This unusual epitope expression has also been demonstrated for several other cell lines of similar origin to 16C1. A 5% subpopulation of C57BL bone marrow has also been defined which binds both the allele-specific antibodies. These cells exist amongst the class I+, Thy-1+, T200+ subpopulation of bone marrow. Anti-Pgp-1 antibodies have been shown to inhibit the thymus-homing capacity of both 16C1 and of bone marrow and have been used to deplete bone marrow of cells capable of reconstituting the T-cell compartment of irradiated mice. All of this indicates at least two distinct Pgp-1 determinants can be expressed by cells from C57BL mice and that antibody specific for either of these determinants can inhibit thymus homing capacity. T-cell precursors which can migrate to thymus would appear to exist amongst the subset of bone marrow cells which express both the Pgp-1.1 and Pgp-1.2 determinants.