Identification and characterization of a monoclonal antibody to an antigen expressed on activated macrophages

A hybridoma clone secreting a monoclonal antibody, designated MA158.2, that reacts with an antigen expressed on lymphokine-treated marcrophages was produced by fusion of mouse myeloma cells with rat spleen cells immunized against C57BL/6 peritoneal macrophages rendered tumoricidal in vitro by incubation with the lymphokine macrophage-activating factor. The specificity of the antibody for activated macrophages and lack of reactivity with histologically diverse cell types was determined by radioimmune indirect binding and flow cytometry. MA158.2 antibody binds to mouse peritoneal macrophages elicited by nonspecific inflammatory agents and to tumoricidal macrophages elicited with Corynebacterium parvum. Resident peritoneal, splenic, and alveolar macrophages were only weakly positive. Several macrophage cell lines (P388D₁, WEH1-231, J774, RAW 264.7), murine fibroblasts, and neutrophils did not bind detectable amounts of MA158.2. Radioimmune indirect binding analysis demonstrated that cell suspensions prepared from C57BL/6 mouse spleen, thymus, and lymph node as well as polymorphonuclear leukocytes, lymphocytes, and T- and B-cell murine lymphomas were MA158.2 negative. Expression of the reactive antigen on the macrophage cell surface was enhanced 3-fold following in vitro activation of elicited macrophages with macrophage-activating factor and the kinetics of activation to the tumoricidal state paralleled the increased expression of the antigen recognized by MA158.2. MA158.2 is a rat IgG2a antibody containing a single specific heavy and light chain that does not detect a polymorphic determinant. This monoclonal antibody will be a useful tool for monitoring the efficacy of agents in activating murine macrophages to the tumoricidal state and in analyzing the sequence of biochemical events that culminate in macrophage activation.