Activation of human monocyte-derived macrophages cultured on Teflon: response to interferon-gamma during terminal maturation in vitro

Abstract

Macrophages (M phi) are potential antitumor effector cells derived from circulating blood monocytes (mo). Most studies on human mo/M phi biology and function have been performed using immature mo precursor cells. However, the conclusions drawn may be questionable, as mo have to undergo terminal differentiation before they reach relevant tissue sites of inflammation and immune reaction. We have analyzed the ability of mo-derived, teflon-cultured M phi to respond to activating stimuli with an increased tumor cytotoxic effector cell function using recombinant interferon-gamma (IFN-gamma), IFN-alpha 2, granulocyte/macrophage colony stimulating factor (GM-CSF), interleukin(IL) 2, IL 1 alpha, and bacterial lipopolysaccharides (LPS) as mediator molecules. It could be shown that the response of M phi to the most potent activator molecule, IFN-gamma, depends on the terminal differentiation from the mo stage to the mature M phi. Whereas adherent mo could be activated only moderately, M phi increased their cytotoxicity by a factor of up to 400. IFN-gamma activation positively correlated with the effector cell number, the time of incubation and the dosage used. Activation did not depend on the presence of LPS, and was lost within 24 to 48 h. LPS itself activated cells only in the microgram range. IFN-alpha 2 activated M phi only at a two log higher concentration than IFN-gamma; GM-CSF was only slightly effective, whereas M phi incubation with IL 1 alpha or IL 2 did not result in M phi activation. Thus, the ability of human M phi to become activated appears to be a function of cellular maturation and is acquired during the terminal step of M phi differentiation. Teflon-cultured M phi could facilitate studies of the activation of human M phi and may be more suitable cells for adoptive immunotherapy in cancer patients than blood monocytes.