Role of Macrophage‐Derived Factors in Generation of Cytotoxic and Antibody Responses

The ability of macrophage subpopulations, separated by virtue of differences in size, to liberate soluble factors able to reconstitute antibody and cell-mediated immune responses in macrophage-depleted lymphoid cultures has been investigated. Evidence is presented to show that all macrophages release trypsin- and pepsin-sensitive molecules with molecular weights of 30,000 to 35,000 and 50,000 to 70,000 that are able to reconstitute only syngeneic lymphocyte responses. In contrast, a molecule(s) with molecular weight of 10,000 to 15,000 daltons is released only by large macrophages and can apparently reconstitute both syngeneic and allogeneic lymphocyte responses. This material is also pepsin-sensitive and, to a lesser degree, trypsin-sensitive.