Ultrastructural study of spontaneous bone marrow rosette-forming cells.

Abstract
Mouse bone marrow contains spontaneous rosette-forming cells (RFC) which include more than 70% T[thymus-derived]-cell precursors, as assessed by their transformation into .theta.-positive cells after incubation with thymic hormone. Such spontaneous RFC, examined in C57Bl/6 mouse bone marrow by EM and scanning electron microscopy, were shown to be small, inactive mouse lymphocytes when macrophages were eliminated by cell preincubation. Thymic hormone target cells apparently include small quiescent lymphocytes.