When Lewis tumor cells (3LL) included in a gel of polyacrylamide microbeads are injected into mice and recovered 1 day later, incorporation of 125I-UdR is strongly reduced. In contrast, no reduction is observed in irradiated mice. The cytostatic effect is non-existent in 6 hr-old granuloma (granulocytes 90%, macrophages 10%), but is maximal in 48 hr-old granuloma (granulocytes 50%, macrophages 50%). When 6 hr-old granuloma cells (which are not cytostatic) are incubated with bone-marrow-derived macrophages (BMs) (which are slightly cytostatic), considerable cytostasis against 3LL is observed, such an effect being strongly reduced if the 2 cell populations are separated. This suggests that close contact of live polymorphs with macrophages is necessary for full expression of cytostasis. No increase in cytostasis of bone-marrow macrophages is observed when BMs are incubated with a cell-free extract of freeze-thawed 6-hr-old granuloma cells. Cell contact is not necessary between granuloma cells and 3LL since the cytostatic activity is found in the supernatant of incubated phagocytic cells. Cytostasis is also observed with B16, P815, J774 cells and normal mouse bone-marrow cells. An active cytostatic fraction has been purified from the supernatant of 48-hr-old granuloma cells following molecular filtration and HPLC. The cytostatic factor has a low molecular weight (400-500 daltons), is not a peptide and presents maximum absorption at 267 nm.

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The term infectious or parasitic disease is used to define a local or systemic pathological state triggered by either viral, bacterial, fungal, or parasitic organisms in the hosts they have passively or actively invaded. Whereas parasites, viruses, and some bacteria, such as Mycobacterium tuberculosis, strictly depend on "their hosts" to achieve their so-called life cycle, other bacterial and fungal microorganisms are entirely independent of animal hosts for proliferation. For example, Listeria monocytogenes are Gram-positive bacteria commonly detected in the external environment, where they live as extracellular organisms. 1 Thus, when L. monocytogenes are isolated from patients in whom local and/or systemic pathogenic processes do develop, they are recognized as "opportunistic bacteria."1 Many different clinical syndromes are initiated by L. monocytogenes in humans who ingested heavily contaminated foods. Invasion by L. monocytogenes may take place at different sites along the digestive tract from its upper part to the intestines. 1 Once Listeria are released within the blood, the various tissues, namely the liver, the spleen, the brain, and the uteroplacental unit, can be invaded. In these sites the bacteria multiply rapidly. Steady-state conditions in the tissues