The development of biological response modifiers and the identification of lymphokines that regulate macrophage (Mφ,) antimicrobial and antitumor activities have attracted great interest [1-3]. Although many of these factors are efficacious in vitro, therapeutically relevant doses are often toxic to normal cells or may cause side effects such as fever, nausea, fatigue, or alterations in white blood cell counts, as is observed when interferon gamma (IFN-γ)  or tumor necrosis factor alpha (TNF-α)  is injected freely into subjects. An additional consideration is that many of the modulators are subject to rapid bioinactivation or excretion. One such example is that of muramyl dipeptide (MDP; N-acetylmuramyl-L-alanyl-D-isoglutamine), a component of the mycobacterium cell wall. Although it is a powerful inducer of Mφ antitumor  and antimicrobial  activities, MDP is excreted from the body within 60 min , thereby limiting its efficacy for therapy in vivo. However, liposomes containing MDP or its lipophilic derivative muramyl tripeptide phosphatidyl-ethanolamine (MTP-PE, amide composed of N-acetylmuramyl-L-alanyl-D-isoglutamyl-L-alanine and dipalmitoyl phosphatidylethanolamine; see Table 1) showed effective activation of Mφs to destroy both tumor cells  and fatal herpes simplex virus type 2 (HSV-2)-infected cells without causing the lysis of uninfected cells . Table 1 202Cells Lines and Tissues Used in Acetyl-LDL Binding Studies Cell type Derivation/elicitation T lymphocyte Primary isolation from thymus B lymphocyte X63-AG8.653 myelomas Endothelial cell Human umbilical vein endothelial (HUVE) cell HL-60 Myeloid, promyelocyte leukemia BMDM CSF-1 -induced bone marrow-derived macrophage Resident macrophage Adherent cells obtained after saline lavage of peritoneum Responsive macrophage Adherent proteose peptone-elicited peritoneal exudate cells Elicited macrophage Adherent thioglycolate-elicited peritoneal exudate cells Fully activated macrophage Adherent C. parvum (P. acne)-e\icited, peritoneal exudate cells.
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