The persisting (P) cell: histamine content, regulation by a T cell-derived factor, origin from a bone marrow precursor, and relationship to mast cells.

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Abstract
Histamine was detected at levels of 100 ng/106 cells in the metachromatic granules of the persisting (P) cell, which appears in cultures of murine lymphoid or bone marrow cells and is capable of long-term growth in vitro in the presence of a T cell-derived growth factor. This factor, which was termed P-cell stimulating factor, was distinct from T-cell growth factor and had an apparent MW of 25,000-30,000. P cells did not originate from Thy.1-positive cells nor was the thymus necessary for the development of their precursors. Moreover, P cells grew directly from colonies generated in agar cultures of bone marrow cells, the nature of the colonies indicating that P cells shared a common precursor with hemopoietic cells. Mutant Wf/Wf mice, although deficient in certain mast cells, possessed P-cell precursors. Apparently, P cells are related to a specialized subset of mast cells, derived from a bone marrow progenitor but regulated by activated T cells.