Biomedical subjects

T Daemen

Publications and source records attributed to T Daemen.

At least 19 recordsLinked to original sources

PubMed2005

Immunologic aspect of ovarian cancer and p53 as tumor antigen.

Ovarian cancer represents the fifth leading cause of death from all cancers for women. During the last decades overall survival has improved due to the use of new chemotherapy schedules. Still, the majority of patients die of this disease. Research reveals that ovarian cancer patients exhibit significant immune responses against their tumor. In this review the knowledge obtained thus far on the interaction of ovarian cancer tumor cells and the immune system is discussed. Furthermore the role of p53 as tumor antigen and its potential role as target antigen in ovarian cancer is summarized. Based on the increased knowledge on the role of the immune system in ovarian cancer major improvements are to be expected of immunotherapy based treatment of this disease.

Journal Article↗

PubMed2005

Induction of human papilloma virus E6/E7-specific cytotoxic T-lymphocyte activity in immune-tolerant, E6/E7-transgenic mice.

Despite promising preclinical results of various therapeutic anticancer immunization strategies, these approaches may not be effective enough to eradicate tumors in cancer patients. While most animal models are based on fast-growing transplantable tumors, malignancies in, for example, cervical cancer patients in general develop much more slowly, which may lead to immune suppression and/or immune tolerance. As a consequence, the immunomodulating signal of any therapeutic immunization regimen should be sufficiently potent to overcome this immunocompromised condition. In previous studies, we demonstrated that an experimental vaccine against human papillomavirus (HPV)-induced cervical cancer, based on Semliki Forest virus (SFV), induces robust HPV-specific cellular immune responses in mice. Now we studied whether this strategy is potent enough to also prime a cellular immune response in immune-tolerant HPV transgenic mice, in which CTL activity cannot be induced using protein or DNA vaccines. We demonstrate that, depending on the route of immunization, SFV-expressing HPV16 E6 and E7 indeed has the capacity to induce HPV16 E7-specific cytotoxic T cells in HPV-transgenic mice.

Animals↗

PubMed2002

A potential role of macrophage activation in the treatment of cancer.

One of the functions of macrophages is to provide a defense mechanism against tumor cells. In the last decades the mechanism of tumor cell killing by macrophages have been studied extensively. The tumor cytotoxic function of macrophages requires stimulation either with bacterial cell wall products such as lipopolysaccharide (LPS) or muramyldipeptide (MDP) or with cytokines such as interferon-gamma (IFN-gamma) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Activated macrophages secrete several substances that are directly involved in tumor cell killing i.e. tumor necrosis factor (TNF) and nitric oxide (NO). On the other hand, substances are secreted that are able to stimulate tumor cell growth, depending on the stage and the nature of the tumor. Several clinical trials have been performed aiming at the activation of macrophages or dendritic cells, a subpopulation of the macrophages. In this review we will summarize and discuss experimental studies and clinical trials based on the activation of macrophages.

Animals↗

PubMed2002

Immunization strategy against cervical cancer involving an alphavirus vector expressing high levels of a stable fusion protein of human papillomavirus 16 E6 and E7.

We are developing immunization strategies against cervical carcinoma and premalignant disease, based on the use of recombinant Semliki Forest virus (SFV) encoding the oncoproteins E6 and E7 from high-risk human papilloma viruses (HPV). Thus far, protein-based, as well as genetic immunization studies have demonstrated low to moderate cellular immune responses against E6 and E7. To improve these responses, we modified the structure and expression level of the E6 and E7 proteins produced by the SFV vector. Specifically, a construct was generated encoding a fusion protein of E6 and E7, while furthermore a translational enhancer was included (enhE6,7). Infection of cells with recombinant SFV-enhE6,7 resulted in the production of large amounts of the E6,7 fusion protein. The fusion protein was more stable than either one of the separate proteins. Immunization of mice with SFV-enhE6,7 resulted in strong, long-lasting HPV-specific cytotoxic T lymphocyte responses. Tumor challenge experiments in mice demonstrated that immunization with SFV-enhE6,7 resulted in prevention of tumor outgrowth and subsequent protection against tumor re-challenge.

Animals↗

PubMed2001

Expression of cyclooxygenase-2 and inducible nitric oxide synthase in human ovarian tumors and tumor-associated macrophages.

This study investigates whether and to what extent cyclooxygenase type-2 (COX-2) and inducible nitric oxide-synthase (iNOS), both known to have an immunosuppressive effect, are expressed in human ovarian tumors. Because COX-2 and iNOS can be expressed by activated macrophages, the presence of tumor-associated macrophages and the expression of COX-2 and iNOS by these tumor-associated macrophages were determined. The results obtained may provide insight into the function of COX-2 and iNOS expression by tumors. The expression of COX-2 and iNOS in tumor cells and macrophages was assessed in 18 malignant, 15 borderline, and 14 benign human ovarian tumors by immunohistochemical staining of frozen tissue sections. The intra- and peritumoral macrophages were stained using an anti-CD68 monoclonal antibody. Most of the malignant tumors (15 of 18), 10 of 15 borderline, and 9 of 14 benign tumors showed COX-2 expression in the epithelial cells, a result which indicates that COX-2 expression is not exclusive to malignancy. In addition, COX-2 staining was more intense in the epithelial cells of benign and borderline tumors than in malignant tumors. Weak iNOS staining was observed in 5 of 18 malignant, 4 of 15 borderline, and 5 of 14 benign tumors. The number of tumor-associated macrophages varied widely between the different tumors. The highest number of tumor-associated macrophages (> or =20/0.125 mm(2)) was observed in malignant tumors, whereas low to moderate intra- and peritumoral macrophage infiltration (5-20/0.125 mm(2)) was observed in the borderline and benign tumors. COX-2-positive tumor-associated macrophages were found in 3 of 18 malignant tumors, 7 of 15 borderline tumors, and 1 of 14 benign tumors. The number of COX-2-positive tumor-associated macrophages ranged from 3 to 30% of the total macrophage population. Some malignant (4 of 18), borderline (5 of 15), and benign (2 of 14) tumors contained iNOS-positive macrophages. Notable was that COX-2- and iNOS-positive macrophages were predominantly located in the tumor stroma, the regions between tumor and stroma, and in the lumina of the tumor when located in the tumor tissue. These data indicate that not only malignant but also borderline and benign ovarian tumors can exhibit increased levels of COX-2 and iNOS expression. In addition, a small proportion of the tumor-associated macrophages found in malignant, borderline, and benign tumors seems to be in an activated state, judged by their iNOS and COX-2 expression. This subpopulation of tumor-associated macrophages was invariably located in the tumor stroma or in the lumina of the tumor, specifically suggesting that macrophages outside the tumor can be tumor cytotoxic.

Adenocarcinoma↗

PubMed2001

Activation of peritoneal cells upon in vivo transfection with a recombinant alphavirus expressing GM-CSF.

In this study we determined the in vivo localization of recombinant proteins expressed by intraperitoneally (i.p.) injected recombinant Semliki Forest virus (SFV) particles. Subsequently, we investigated the influence of i.p. administered SFV particles encoding recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF) on intraperitoneal recruitment and activation of cells. Finally, the therapeutic effect of SFV-GM-CSF treatment on an i.p. growing ovarian tumor was determined. Intraperitoneal injections of recombinant SFV particles encoding the reporter protein luciferase resulted in a high level of luciferase activity in cells of the peritoneal lining and tumor cells in the peritoneal cavity. Low levels of luciferase activity were found in liver, spleen and lungs. Injection of SFV-GM-CSF particles resulted in a slight increase in the number of peritoneal macrophages and in a significant increase in the number of neutrophils. In contrast to multiple i.p. injections with commercially available recombinant GM-CSF, i.p. injected SFV-GM-CSF particles activated the macrophages to tumor cytotoxicity. Although treatment of tumor-bearing mice with SFV-GM-CSF particles did not result in prolonged survival, tumor growth was inhibited for 2 weeks. Our findings indicate that macrophage-activating cytokines expressed by the efficient and safe recombinant SFV system when administered i.p. may provide an immunotherapeutic treatment modality additional to current chemotherapeutic treatment of intraperitoneally growing cancers.

Animals↗

PubMed2001

Replication-defective recombinant Semliki Forest virus encoding GM-CSF as a vector system for rapid and facile generation of autologous human tumor cell vaccines.

This paper describes the production of recombinant Semliki Forest virus encoding murine or human granulocyte-macrophage colony-stimulating factor (GM-CSF) and the capacity of these vectors to transduce murine and human tumor cells ex vivo. High-titer stocks (up to 3 x 10(9) particles/ml) of conditionally infective, replication-defective, recombinant SFV particles were generated using the SFV Helper-2 system. It is shown that the recombinant SFV/GM-CSF virus, as well as recombinant SFV carrying the beta-galactosidase reporter gene, efficiently transduce both murine tumor cell lines as well as primary human renal carcinoma cells. Using ELISA's specific for GM-CSF, levels of GM-CSF production by the cells were determined. Levels of murine GM-CSF (mGM-CSF) produced by SFV/mGM-CSF transduced renal cell cancer cultures were equal to or higher than corresponding levels reported in the literature after transduction of similar renal carcinoma cell cultures using a retroviral vector system. The biological activity of GM-CSF was demonstrated by using cells which are dependent on GM-CSF for growth and by using primary bone marrow cells. All the transduced cell cultures (including the human renal cell carcinoma samples) produced GM-CSF for up to at least 4 days after transduction. The results imply that the recombinant SFV system can be used for rapid and facile preparation of autologous cancer cell vaccines.

Animals↗

PubMed2000

Induction of cytotoxic T lymphocyte activity by fusion-active peptide-containing virosomes.

Priming of cytotoxic T lymphocyte (CTL) activity with exogenous antigen requires introduction of the antigen into the MHC class I presentation pathway of antigen-presenting cells. In the present study, we used fusogenic reconstituted envelopes (virosomes), derived from influenza virus, as a carrier system for delivery of a synthetic soluble peptide corresponding to a major murine CTL epitope of the influenza virus nucleoprotein (NP). Virosomes containing encapsulated NP-peptide efficiently sensitized target cells for recognition by influenza-specific CTLs generated through priming of mice with infectious virus. Intramuscular immunization of mice with peptide-containing virosomes induced a potent class I MHC-restricted CTL response against influenza-infected target cells. By contrast, an equal dose of NP-peptide encapsulated in fusion-inactivated virosomes did not induce CTL activity, indicating an essential role of the membrane fusion activity of the virosomes in the induction of the response. Likewise, NP-peptide encapsulated in liposomes, NP-peptide mixed with empty virosomes and NP-peptide in IFA failed to induce a CTL response. These results demonstrate that fusion-active virosomes represent a promising delivery system for induction of class I MHC-restricted CTL activity with non-replicating viral antigens.

Animals↗

PubMed2000

Genetic immunization against cervical carcinoma: induction of cytotoxic T lymphocyte activity with a recombinant alphavirus vector expressing human papillomavirus type 16 E6 and E7.

Infection of genital epithelial cells with human papillomavirus (HPV) types 16 and 18 is closely associated with the development of cervical carcinoma. The transforming potential of these high-risk HPVs depends on the expression of the E6 and E7 early viral gene products. Since the expression of E6 and E7 is selectively maintained in premalignant and malignant cervical lesions these proteins are attractive candidates for immunotherapeutic and prophylactic strategies. This report describes the construction, characterization and the in vivo immunotherapeutic potential of recombinant Semliki Forest virus (SFV) expressing the HPV16 E6 and E7 proteins (SFV-E6E7). Western blot analysis and immunofluorescence staining demonstrated expression of E6 and E7 in BHK cells infected with SFV-E6E7. Immunization of mice with SFV-E6E7 resulted in an efficient in vivo priming of HPV-specific CTL activity. The induced CTL lysed murine tumor cells transformed with the HPV16 genome and EL4 cells loaded with an immunodominant class I-binding HPV E7 peptide. CTLs could reproducibly be induced by immunization with three injections of as few as 10(5) infectious units of SFV-E6E7. Protection from tumor challenge was studied using the tumor cell line TC-1. Immunization with 5 x 10(6) SFV-E6E7 particles protected 40% of the mice from tumor challenge. These results indicate that E6E7 expression by the efficient and safe recombinant SFV system represents a promising strategy for immunotherapy or immunoprophylaxis of cervical carcinoma.

Animals↗

PubMed1999

Effect of intraperitoneally administered recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF) on the cytotoxic potential of murine peritoneal cells.

We studied the effect of recombinant murine granulocyte-macrophage colony-stimulating factor (rmGM-CSF) on the cytotoxic potential of murine peritoneal cells. Mice received rmGM-CSF intraperitoneally using different dosages and injection schemes. At different time points after the last injection, mice were sacrificed, peritoneal cells isolated and their tumour cytotoxicity was determined by a cytotoxicity assay using syngeneic [methyl-3H]thymidine-labelled colon carcinoma cells. Also, the cytotoxic response to a subsequent in vitro stimulation with lipopolysaccharide was determined. Upon daily injection of 6000-54,000 U rmGM-CSF over a 6-day period, the number of peritoneal cells increased over ten fold with the highest rmGM-CSF dose. Increases in cell numbers was mainly due to increases in macrophage numbers. Upon injection of three doses of 3000 U rmGM-CSF per day for 3 consecutive days, the number of macrophages remained elevated for minimally 6 days. Although the peritoneal cells from rmGM-CSF-treated mice were not activated to a tumoricidal state, they could be activated to high levels of cytotoxicity with an additional in vitro stimulation of lipopolysaccharide. Resident cells isolated from control mice could be activated only to low levels of tumour cytotoxicity with lipopolysaccharide. Tumour cytotoxicity strongly correlated with nitric oxide secretion. When inhibiting nitric oxide synthase, tumour cell lysis decreased. Thus, the expanded peritoneal cell population induced by multiple injections of rmGM-CSF has a strong tumour cytotoxic potential and might provide a favourable condition for immunotherapeutic treatment of peritoneal neoplasms.

Animals↗

PubMed1999

[3H]thymidine incorporation into whole liver as an alternative to [3H]thymidine incorporation into DNA as a parameter of cell proliferation in regenerating liver tissue in rats.

OBJECTIVE: To monitor liver regeneration following partial hepatectomy, liver cell proliferation can be measured by assaying in vivo [3H]thymidine incorporation into liver cell DNA. We hypothesized that [3H]thymidine incorporation into whole liver tissue parallels [3H]thymidine incorporation into liver cell DNA, both in high proliferating and low proliferating liver. STUDY DESIGN: Liver cell proliferation in rats after partial hepatectomy or a sham operation was studied by measuring incorporation of [3H]thymidine into various fractions of liver tissue on days 1, 2, 3, 4 and 10 after surgery. RESULTS: [3H]thymidine incorporation into whole liver tissue and in the protein fraction correlated well with DNA-specific [3H]thymidine incorporation into regenerating (r > .80, P < .0001) and nonregenerating liver (r > .69, P < .005). [3H]thymidine incorporation into DNA was < 5% of the total amount of administered [3H]thymidine in both sham-operated and hepatectomized rats. Significant differences in [3H]thymidine incorporation into partially hepatectomized livers as compared to sham-operated rat livers were found on days 1 and 2 (whole liver tissue and protein fraction) or day 1 (DNA) after surgery. CONCLUSION: [3H]thymidine incorporation into whole liver tissue is a simple technique that can be used for the study of liver cell proliferation after partial hepatectomy in rats.

Animals↗

PubMed1997

Different intrahepatic distribution of phosphatidylglycerol and phosphatidylserine liposomes in the rat.

Liposomes with diameters of 200 to 400 nm containing phosphatidylserine (PS) or phosphatidylglycerol (PG) were injected intravenously into rats. Two hours after injection, 75% of the injected dose of PS liposomes was found in the liver and only 10% found in the spleen, while 35% of the PG liposomes was found in the liver and as much as 40% was found in the spleen. Cell-isolation experiments revealed the following remarkable difference in the intrahepatic distribution between the two liposome formulations: the PS liposomes distributed in about equal amounts to Kupffer cells and hepatocytes, despite their size (200-400 nm) exceeding that of the endothelial fenestrae (average 150 nm), whereas the PG liposomes were only taken up by the Kupffer cells and not at all by the hepatocytes. Double-label studies, using liposomes in which the lipid-moiety was radio labeled with [3H]cholesteryloleylether ([3H]CE) and the water phase with [14C]sucrose, showed that the liposomes were taken up as intact particles. These observations were confirmed through electron microscopy by determining the in situ localization of liposome-encapsulated colloidal gold particles in thin sections of liver and spleen. The differences in organ distribution are ascribed to differences in opsonization patterns of the two liposomal surfaces. For the difference in intrahepatic distribution, we offer the following two explanations: the exploitation of the blood cell-mediated forced sieving concept and the indication of a PS-specific pharmacological effect on the dimensions of the fenestrations.

Animals↗

PubMed1996

Liposomal phosphatidylserine inhibits tumor cytotoxicity of liver macrophages induced by muramyl dipeptide and lipopolysaccharide.

Liposomes can very efficiently deliver immunomodulators to macrophages so as to induce tumor cytotoxicity. Liposomes most widely used for that purpose contain negatively charged lipids, in particular phosphatidylserine (PS), to enhance liposome uptake by the macrophages. We investigated the effect of three negatively charged liposomal lipids on the in vitro activation of liver macrophages to tumor cytotoxicity by muramyl dipeptide (MDP) and lipopolysaccharide (LPS). Both MDP- and LPS-induced tumor cytotoxicity towards murine colon adenocarcinoma cells were strongly inhibited by PS-containing liposomes. Under comparable conditions phosphatidylglycerol (DPPG)-containing or dicetyl phosphate (DCP)-containing liposomes did not inhibit or only marginally inhibited the induction of tumor cytotoxicity. We did not observe PS-mediated inhibition of tumor cell toxicity when the exposure of the macrophages to PS-liposomes was limited to the 4-h activation period prior to addition of the tumor target cells, suggesting that the inhibitory effect is accomplished at the level of the later stages of the activation process. Previously, we showed that macrophages which are activated to tumor cytotoxicity during a 24-h incubation with MDP become refractory to a second activation with MDP. Now we observed that simultaneous incubation with PS-containing liposomes partially prevents this refractoriness, which is also compatible with an interfering action of PS at a relatively late stage in the activation process. We conclude that PS, despite its reported stimulatory effect on liposome uptake by macrophages, can seriously antagonize the effectiveness of immunomodulating agents acting on macrophages. This bears relevance to the use of PS-containing liposomes as a vehicle for such agents. The results are discussed in perspective of earlier reported pharmacological effects of PS and its metabolites.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed1995

Liposomal doxorubicin-induced toxicity: depletion and impairment of phagocytic activity of liver macrophages.

Doxorubicin entrapped within conventional liposomes (200 nm in diameter; lip-Dox) has major toxic effects on liver macrophages of the rat for a considerable period of time following i.v. administration, with respect to both specific phagocytic capacity and cell numbers. At different time-points after injection of lip-Dox or free doxorubicin, radiolabeled, negatively charged, "empty" test liposomes were injected. Phagocytic capacity was determined by isolating the liver macrophages and measuring the amount of macrophage-associated radioactivity. Four subfractions of liver macrophages of different cell-size and with intrinsically different phagocytic capacity were isolated. Twenty-four hours after injection of lip-Dox, the phagocytic capacity of the larger-sized liver macrophages was strongly decreased. The relatively low intrinsic phagocytic capacity of the smaller-sized macrophages was only slightly impaired. Phagocytic capacity after injection of lip-Dox was nearly restored to control values after 14 days. Blood clearance of Klebsiella pneumoniae bacteria after pre-treatment with lip-Dox was strongly decreased. Pre-treatment with the free drug and/or placebo liposomes had no effect on phagocytic and bacterial blood-clearance capacity. A major depletion of the liver macrophage population was observed, as revealed by both macrophage isolation and histology. Only 2 weeks after injection of lip-Dox, the number of cells had returned to that seen in control animals. In view of the important host-defense functions of the liver macrophages, especially in the control of tumor growth and infection, the findings reported here should be taken into consideration when lip-Dox is to be administered in anti-tumor therapy.

Animals↗

PubMed1995

Tumoricidal response of liver macrophages isolated from rats bearing liver metastases of colon adenocarcinoma.

Intraportal inoculation of CC531 adenocarcinoma cells into syngeneic rats causes an increase of liver macrophage cell number but not of major histocompatibility complex class II antigen expression. On day 1 after inoculation of 10(5) CC531 cells, a fixed number of isolated liver macrophages lysed significantly more target cells in vitro than did control cells. This effect was still present after 4 weeks. A 10-fold higher initial tumor dose significantly suppressed the macrophage response during the first 2 weeks. In contrast to tumoricidal activity induced by lipopolysaccharide in vitro, the tumoricidal response following in vivo challenge with tumor cells appeared not closely related to the production of reactive nitrogen intermediates, as in the latter case it was not abrogated in the presence of nitric oxide synthase inhibitor. Furthermore, the liver macrophage population appeared not fully activated after tumor inoculation as lipopolysaccharide further increased tumoricidal activity in vitro. The observed numerical and functional response of liver macrophages to intraportally inoculated tumor cells points at an important role of these cells in aspecific immune reactivity aimed at the reduction of local tumor growth. Results suggest that mechanistic differences exist between macrophage tumoricidal activity induced by tumor cells as compared with lipopolysaccharide.

Adenocarcinoma↗

PubMed1995

Antitumor reactivity induced by liposomal MTP-PE in a liver metastasis model of colon cancer in the rat.

The antitumor effects of muramyl tripeptide phosphatidylethanolamine, incorporated within the lipophilic phase of liposomes (lipMTP-PE) were studied using a model of liver metastasis of colon cancer in the rat. Intravenous immunotherapy with lipMTP-PE, when started 2 days before the inoculation of tumor cells and given twice a week, significantly reduced subsequent tumor growth in the liver. The main effect of treatment appeared to be a substantial local increase in the number of tumoricidal macrophages and lymphocytes. Tumor cell lysis by isolated macrophages in vitro, however, appeared not to be elevated above the level triggered by tumor growth alone. Therefore, the observed therapeutic effect of lipMTP-PE probably results from a combination of (1) an increase in the number of cytotoxic macrophages at the onset of metastatic growth in the liver, thus increasing the probability of lethal contacts between tumoricidal effectors and tumor cells and (2) indirect effects of lipMTP-PE, via the induction of cytokine production by liver macrophages, leading to increased numbers and/or activity of cytotoxic lymphocytes and natural killer cells.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed1995

Histochemical and electron microscopic characterization of hepatic macrophage subfractions isolated from normal and liposomal muramyl dipeptide treated rats.

Subfractions of the hepatic macrophage population, differing in cell size, were isolated from normal rats and rats treated with liposomal muramyl dipeptide (lipMDP) and analyzed histochemically and by ultrastructural peroxidase cytochemistry. The majority of cells in all subfractions of control rats displayed the ultrastructural endogenous peroxidase pattern of resident liver macrophages and showed positive staining with the general macrophage markers nonspecific esterase (NSE) and monoclonal antibody ED1. Heterogeneity in intensity of NSE and ED1 staining was observed among macrophages of different size. Generally, the intensity of NSE and ED1 staining decreased with decreasing cell size. After injection of lipMDP, we observed the appearance of a discrete subpopulation of cells in the liver in addition to the resident macrophages. These cells, containing a nucleus with a characteristic shape, were predominantly recovered in the small-sized fractions and were characterized by an immature ultrastructural macrophage morphology (no or only a few lysosomes and phagosomes) and a lack of ED1 reactivity, NSE, and endogenous peroxidase. We suggest an important role for these cells in lipMDP induced antitumor capacity of the liver.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed1995

Heterogeneity in secretory responses of rat liver macrophages of different size.

Four subpopulations of hepatic macrophages, differing in size, were isolated from rat liver. The secretion of nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha), prostaglandin E (PGE) and interleukin-1 (IL-1) by freshly isolated as well as cultured cells was studied after in vitro stimulation with the immunomodulator muramyl dipeptide (MDP) in free or liposome-encapsulated form. Freshly isolated liver macrophages could be induced to secrete significant levels of NO, TNF-alpha, PGE and IL-1. The extent of secretion, however, varied substantially between macrophages of different size. The highest levels of secretion of TNF-alpha, PGE and IL-1 were observed in the fraction containing the large-size macrophages, while progressively lower levels of secretion were observed with decreasing size. In contrast, the highest levels of NO secretion were observed by small macrophages and steadily decreased with increasing size. Hepatic macrophages of different size displayed differences in secretory potential during in vitro culture. The ability of small liver macrophages to secrete NO, TNF-alpha, or PGE, following activation with MDP, gradually increased with time in culture. In contrast, large liver macrophages gradually lost their secretory ability after 1-2 days and the intermediate-size cells after 2-3 days in culture. This functional heterogeneity in secretory properties among rat liver macrophages of different size is discussed with reference to their potential role and significance in host defense against metastatic tumor growth in the liver.

Animals↗