Experimental murine schistosomiasis mansoni: hyperplasia of the mono-macrophage cell lineage and stimulation of myeloid proliferation by peripheral macrophages.

1. Normal and schistosome-infected mice were similar in terms of the total number of bone marrow myeloid cell precursors and their proliferative capacity in vitro when stimulated with supernatants of L-929 cells containing M-CSF. 2. Delayed differentiation of bone marrow neutrophil granulocytes and blood monocytosis of infected animals were consistent with a modification in the differentiation of bone marrow myeloid precursors, favoring the production of a mono-macrophage cell lineage. 3. Macrophages isolated from periovular granulomas secreted a considerable stimulatory activity for the proliferation of the mono-macrophagic cell lineage, whereas peritoneal macrophages from the same animals had only a very low stimulatory activity. 4. We conclude that systemic hyperplasia of mono-macrophagic cells in schistosomiasis may be related to their increased release from the bone marrow and to their peripheral amplification in inflammatory tissue infiltrate as a consequence of the local production of stimulatory activity for their proliferation.