Dissociation of effector functions in populations of activated macrophages

Abstract

THERE is much evidence to indicate an important role for activated macrophages in resistance to malignant tumours and to infections caused by intracellular pathogens. Different investigators have found that activated macrophages may be distinguished from normal macrophages by either morphological, biochemical, or functional criteria, depending on the experimental design¹. Functional criteria frequently cited are killing of intracellular organisms^2,3, inhibition and/or killing of tumour cells^4–6 and inhibition of proliferating lymphocytes^7,8. Previous work in our laboratory has demonstrated that macrophages activated by several methods have always exhibited each of these three functional capacities. For example, macrophages activated by either chronic infection with C56 strain Toxoplasma gondii or by killed Corynebacterium parvum inhibited multiplication of T. gondii^9–11, DNA synthesis by tumour target cells^12,13, and mitogen- and antigen-specific lymphocyte transformation¹⁴. Whether different populations of activated macrophages which have been defined by one functional criterion always possess the other functional capacities of activated macrophages as well, however, has not been established. We report here that activated macrophages characterised by one functional criterion do not necessarily possess other functional characteristics of activated macrophages and that differences in functional capacity depend on the method used to activate the macrophages.