Characterization of stimulator cells for alloreactive cytotoxic-T-lymphocyte responses in vivo.

Mouse spleen cells were fractionated and tested for their ability to induce alloreactive cytotoxic-T-lymphocyte responses in vivo. The cells with allostimulatory potential are enriched maximally in a population of low density, Ig-negative, Thy 1-negative cells. This fraction has the cytochemical and ultrastructural characteristics of cells of the early myeloid series and not those of typical dendritic cells or macrophages. These myeloid cells represent a new subset of accessory cells which could be a potential source of allostimulation in organ grafts. They should be considered along with other accessory cell types as potential elements which induce transplantation responses.