The in situ immune response of the rat after intraperitoneal depletion of macrophages by liposome-encapsulated dichloromethylene diphosphonate.

This study concerns the contribution of peritoneal macrophages in vivo to local and systemic immune responses in the rat. Peritoneal macrophages as well as macrophages in the draining parathymic lymph nodes were selectively eliminated by intraperitoneal inoculation of dichloromethylene-diphosphonate-containing liposomes. This depletion resulted in an enhanced immune reaction to intraperitoneally administered trinitrophenyl keyhole limpet haemocyanin in the parathymic lymph nodes, as demonstrated by the higher numbers of specific anti-TNP antibody-forming cells in macrophage-depleted animals than in control animals from day 5 after immunization. The immune reaction peaked at day 7 and remained high until day 10. Specific antibody-forming cells were found occasionally in the mesenteric lymph nodes and spleen, but not in the mucosa of the gut or in the bronchus-associated lymphoid tissue. An elevated immune reaction found in parathymic lymph nodes associated with the depletion of local macrophages by liposome treatment indicates a regulatory role of peritoneal macrophages in local humoral immune response.