Progenitor cells in the bone marrow and the spleen of mice, whether infected with Schistosoma japonicum or not, formed cell clusters and colonies when incubated with culture supernatant fluid of spleen cells incubated with soluble egg antigen (SEA). The egg extract, up to a concentration of 250 micrograms/ml protein, did not directly stimulate progenitor cell proliferation in the bone marrow. Eosinophilia in mice infected with S. japonicum may be mediated indirectly by egg antigen-stimulated immune lymphocytes and not directly by the egg antigen.</p
