Immunological tolerance and tumor rejection in embryo-aggregated chimeric mice - lessons for tumor immunity.

Background: Rejection of transplanted tumors by the immune system is a rare event in syngeneic hosts, and is considered to be dependent on the local interaction of defensive immune reactions and tumor tolerance mechanisms. Here, we have enlisted the aid of a unique set of embryo-aggregated lineage chimeric mice derived from C57/BL6 and FVB donors to study the interplay between local and systemic tumor immunity and tolerance in rejection of mouse B16 melanoma cells, syngeneic to the C57/BL6 donor strain.

Methods: Two variants of embryo-aggregated chimeric mice with either variable or no contribution of C57-derived cells to their skin were generated by the fusion of different ratios of morula stage blastomers.

TNF revisited: TNF-independent antitumor activity in sera of mice sensitized with Propionibacterium acnes and challenged with lipopolysaccharide.

Sera of mice sensitized with bacteria and subsequently challenged with lipopolysaccharide promote hemorrhagic necrosis of tumors in vivo and display cytotoxic activity against tumor cells in vitro, which has been attributed to the induction of tumor necrosis factor (TNF). Here, we describe the induction of a previously unrecognized antitumor activity in such sera, which is distinct from TNF but displays tumor-specific cytocidal activity in vitro as well as potent tumor-regressing activity in vivo. Biochemical analysis of this activity yielded a molecular mass of approximately 150 kDa, closely resembling a novel tumoricidal factor of murine macrophages (Mphi) termed MTC 170 (Mphi tumor cytotoxin, approximate molecular mass 170 kDa), which we have previously proposed to constitute a major effector pathway for the destruction of tumor cells by activated Mphi.

Activation of macrophage tumoricidal activity by photodynamic treatment in vitro--indirect activation of macrophages by photodynamically killed tumor cells.

Macrophages constitute a major part of natural tumor defense by their capacity to destroy selectively a broad range of tumor types upon specific activation. In the last couple of years, these cells have also been implicated as effector cells in the destruction of tumors by photodynamic therapy. In the present work, the potential role of macrophage-mediated tumor cytotoxicity after photodynamic treatment in vitro has been investigated with respect to photodynamic activation of macrophages for tumoricidal effector functions.

Cutting edge: differential effect of apoptotic versus necrotic tumor cells on macrophage antitumor activities.

Macrophages (Mphi) play essential roles both in tumor defense and normal tissue homeostasis by removal of transformed as well as damaged and disintegrating cells. Whereas tissue necrosis is known to provoke inflammatory responses, removal of apoptotic cells has been assumed to be immunologically inert. We now show that while Mphi exposure to necrotized tumor cells causes pronounced stimulation of Mphi antitumor activity, exposure of Mphi to apoptotic tumor cells in contrast results in impairment of Mphi-mediated tumor defense and even support of tumor cell growth.

Effect of photodynamic pretreatment on the susceptibility of murine tumor cells to macrophage antitumor mechanisms.

In vitro photodynamic treatment of YAC-1 murine T-lymphoma cells with the hematoporphyrin derivative Photosan 3 and red light resulted in dose-dependent phototoxicity. Photodynamic pretreatment, however, did not render these cells more susceptible to macrophage-mediated tumor cytotoxicity or the cytotoxic effects of macrophage-derived antitumor mediators like tumor necrosis factor alpha (TNF-alpha) or interferon beta (IFN-beta). Independent of the degree of photosensitization used, the cytotoxicity values obtained with macrophages or the different mediators were shifted by the respective values for phototoxicity, suggesting these effects to be additive and thus not interdependent.

A fast and sensitive method for detection of phospholipid-binding proteins on nitrocellulose membranes.

We describe a sensitive new method for specific detection and quantitation of phospholipid-binding proteins using two purified lipocortins as model proteins. The method consists of blotting proteins to nitrocellulose membranes followed by incubation with radiolabeled phospholipids and autoradiographic detection of bound phospholipids. It allows specific detection of phospholipid binding proteins to a threshold of about 100 ng/spot and their quantitation up to several micrograms as well as rapid analysis of specific phospholipid binding properties of individual proteins.

Characterization and partial purification of a high molecular weight tumoricidal activity secreted by murine bone marrow macrophages.

Cultured murine bone marrow-derived macrophage (BMM phi) can be induced to secrete tumoricidal activity in vitro when activated with recombinant IFN-gamma and bacterial lipopolysaccharide (LPS). We have analyzed this activity for tumor specificity, relationship to tumor necrosis factor-alpha (TNF-alpha), serine proteases, and reactive nitrogen intermediates, and partially purified this activity by high pressure liquid chromatography. Cytolytic activity was recovered in conditioned culture supernatants of serum-free cultivated BMM phi treated with a combination of IFN-gamma and LPS but was not inducible by either stimulant alone.

Human macrophages secrete a tumoricidal activity distinct from tumour necrosis factor-alpha and reactive nitrogen intermediates.

Human macrophages, differentiated in vitro from blood monocytes, can be induced to secrete tumouricidal activity when activated by combined treatment with recombinant interferon gamma and bacterial lipopolysaccharide. We have analysed conditioned culture supernatants of activated human monocytes and in vitro differentiated macrophages cultivated under serum-free conditions for cytolytic activity against a TNF alpha-insensitive human tumour cell line and characterized this activity with respect to its relationship to TNF alpha and reactive nitrogen intermediates. Cytolytic activity was recovered in the high molecular weight fraction of culture supernatants conditioned by terminally differentiated macrophages, whereas conditioned culture supernatants of freshly isolated blood monocytes, processed under identical conditions, were devoid of significant cytolytic activity.

Tumoricidal effector molecules of murine macrophages.

Activated macrophages secrete a variety of factors affecting proliferation or viability of neoplastic cells. Factors described previously are discussed for their relevance as effector molecules for the selective destruction of tumor cells by activated macrophages and compared to a recently characterized high-molecular-weight tumoricidal activity secreted by activated murine bone-marrow-derived macrophages.

Fungicidal activity of IFN-gamma-activated macrophages. Extracellular killing of Cryptococcus neoformans.

Cryptococcus neoformans is an encapsulated yeast-form fungus which causes pulmonary and meningeal infections preferentially in the immunocompromised host. It is thought that cell-mediated immunity is important for acquired resistance against cryptococcosis with activated macrophages as the final effector cells. However, specific polysaccharides in the capsule of C.

Changes in the expression of macrophage antigens associated with activation for tumor cell killing.

Cultured murine bone marrow macrophages (BMM phi) can be induced to kill tumor cells in vitro by combined treatment with a priming (IFN-gamma) and a triggering (LPS) agent. We have examined the expression of cellular antigens accompanying this activation by Western blot analysis with rabbit antisera raised against unstimulated and fully activated BMM phi and assayed the effect of these antisera on macrophage-mediated tumor cytotoxicity. Killing of Yac-1 target cells was slightly enhanced by antiserum against unstimulated BMM phi but inhibited 54% by antiserum against activated BMM phi.