The selective engulfment of apoptotic bodies by dendritic cells is mediated by the αvβ3 integrin and requires intracellular and extracellular calcium

Dendritic cells derived in vitro from monocytes are known to be poor phagocytes. Here we show that, unlike macrophages, monocyte-derived dendritic cells indeed fail to take up opsonized particles or necrotic cells; however, apoptotic bodies are efficiently engulfed by dendritic cells. The temperature dependence and the sensitivity to cytochalasin D indicate that the apoptotic body engulfment is representative of early stages of phagocytosis. Inhibition studies with ligands for surface molecules involved in recognition of apoptotic bodies, such as vitronectin receptor, CD36 and phosphatidylserine receptor, revealed that apoptotic body engulfment by dendritic cells is mediated preferentially by the vitronectin receptor αvβ3, while all the receptors, with different efficiency, are engaged in phagocytosis of apoptotic bodies by macrophages. The interaction between apoptotic bodies and dendritic cells elicits a rise in intracellular free calcium concentration ([Ca²⁺]_i) which is essential for the process of engulfment. Either intra- or extracellular Ca²⁺ buffering inhibits apoptotic body engulfment by dendritic cells and [Ca²⁺]_i increases, indicating the involvement of both intra-and extracellular Ca²⁺. In contrast, Ca²⁺ mobilization is dispensable for macrophage phagocytosis of apoptotic bodies. The different requirements of Ca²⁺ in macrophages and dendritic cells is possibly due to the differential usage of phagocytic receptors (CD36 vs. αvβ3) and might reflect different fates of apoptotic bodies in the two cell types.     

Disruption of HLA class II antigen presentation in Burkitt lymphoma: implication of a 47 000 MW acid labile protein in CD4+ T‐cell recognition

While Burkitt lymphoma (BL) has a well‐known defect in HLA class I‐mediated antigen presentation, the exact role of BL‐associated HLA class II in generating a poor CD4⁺ T‐cell response remains unresolved. Here, we found that BL cells are deficient in their ability to optimally stimulate CD4⁺ T cells via the HLA class II pathway. This defect in CD4⁺ T‐cell recognition was not associated with low levels of co‐stimulatory molecules on BL cells, as addition of external co‐stimulation failed to elicit CD4⁺ T‐cell activation by BL. Further, the defect was not caused by faulty antigen/class II interaction, because antigenic peptides bound with measurable affinity to BL‐associated class II molecules. Interestingly, functional class II–peptide complexes were formed at acidic pH 5·5, which restored immune recognition. Acidic buffer (pH 5·5) eluate from BL cells contained molecules that impaired class II‐mediated antigen presentation and CD4⁺ T‐cell recognition. Biochemical analysis showed that these molecules were greater than 30 000 molecular weight in size, and proteinaceous in nature. In addition, BL was found to have decreased expression of a 47 000 molecular weight enolase‐like molecule that enhances class II‐mediated antigen presentation in B cells, macrophages and dendritic cells, but not in BL cells. These findings demonstrate that BL likely has multiple defects in HLA class II‐mediated antigen presentation and immune recognition, which may be exploited for future immunotherapies.     

Crystalloid inclusions in brain macrophages and hemopoietic tissue in GFAP-IL3 mice resemble inclusions identified in multiple sclerosis

Crystalloid inclusions or "pole bodies" observed in brain macrophages in human demyelinating disease represent a morphological enigma. Similar inclusions were detected in brain macrophages from the GFAP-IL3 mouse, a transgenic murine model for macrophage mediated demyelination. Mice also showed inclusions in hematopoietic tissue. They appear to be related to phagocytosis and secretion, respectively, as evidenced by the fact that in phagocytosing cells they often merged with lysozomes and that affected cells showed empty channels open to the interstitium. Based on ultrastructural and immunolocalization studies using chaperonin-10, lysozyme, and cathepsin the authors suggest that these inclusions are consistent with phagocytosis-related secretory products. This study may provide insight into the nature and significance of similar macrophage inclusions recently identified in multiple sclerosis.     

Crystalloid Inclusions in Brain Macrophages and Hemopoietic Tissue in GFAP-IL3 Mice Resemble Inclusions Identified in Multiple Sclerosis

Crystalloid inclusions or "pole bodies" observed in brain macrophages in human demyelinating disease represent a morphological enigma. Similar inclusions were detected in brain macrophages from the GFAP-IL3 mouse, a transgenic murine model for macrophage mediated demyelination. Mice also showed inclusions in hematopoietic tissue. They appear to be related to phagocytosis and secretion, respectively, as evidenced by the fact that in phagocytosing cells they often merged with lysozomes and that affected cells showed empty channels open to the interstitium. Based on ultrastructural and immunolocalization studies using chaperonin-10, lysozyme, and cathepsin the authors suggest that these inclusions are consistent with phagocytosis-related secretory products. This study may provide insight into the nature and significance of similar macrophage inclusions recently identified in multiple sclerosis.     

Vaccinia virus decreases major histocompatibility complex (MHC) class II antigen presentation,T-cell priming,and peptide association with MHC class II

Vaccinia virus (VACV) is the current live virus vaccine used to protect humans against smallpox and monkeypox, but its use is contraindicated in several populations because of its virulence. It is therefore important to elucidate the immune evasion mechanisms of VACV. We found that VACV infection of antigen-presenting cells (APCs) significantly decreased major histocompatibility complex (MHC) II antigen presentation and decreased synthesis of 13 chemokines and cytokines, suggesting a potent viral mechanism for immune evasion. In these model systems, responding T cells were not directly affected by virus, indicating that VACV directly affects the APC. VACV significantly decreased nitric oxide production by peritoneal exudate cells and the RAW macrophage cell line in response to lipopolysaccharide (LPS) and interferon (IFN)-γ, decreased class II MHC expression on APCs, and induced apoptosis in macrophages and dendritic cells. However, VACV decreased antigen presentation by 1153 B cells without apparent apoptosis induction, indicating that VACV differentially affects B lymphocytes and other APCs. We show that the key mechanism of VACV inhibition of antigen presentation may be its reduction of antigenic peptide loaded into the cleft of MHC class II molecules. These data indicate that VACV evades the host immune response by impairing critical functions of the APC.     

An analysis of the role of skin Langerhans cells (LC) in the cytoplasmic processing of HIV-1 peptides after “Peplotion” transepidermal transfer and HLA class I presentation to CD8+ CTLs—An approach to immunization of humans

Skin Langerhans cells (LC) are antigen-presenting cells capable of expressing MHC class I and class II molecules on the plasma membrane. This molecular activity was reviewed to combine the knowledge of peptide presentation by MHC and HLA class I and class II molecules to prime CD8⁺ cytotoxic T cells (CTLs) and CD4⁺ T helper cells, respectively. The possible utilization of the skin dendritic cells for the development of antiviral CTLs and antibodies by synthetic peptides modeled according to the motifs of peptides that naturally interact with the peptide binding grooves of the various HLA haplotypes is discussed and evaluated. It may be possible that the introduction of synthetic viral peptides with motifs to fit the HLA class I haplotypes of a human population to the skin dendritic cells will prime selectively the cellular or the humoral immune responses. This approach may provide a new vaccination technique that applies synthetic virus peptides as vaccines for the immunization of humans. The neuropeptide CGRP interacts with LC and modulates antigen presentation.     

Impaired macrophage phagocytosis of apoptotic neutrophils in patients with human immunodeficiency virus type 1 infection

Dysfunction of neutrophils (polymorphonuclear leukocytes [PMNL]) and macrophagic cells occurs as a consequence of human immunodeficiency virus type 1 (HIV-1) infection. Macrophages contribute to the resolution of early inflammation ingesting PMNL apoptotic bodies. This study investigated macrophage ability to phagocytose PMNL apoptotic bodies in patients with HIV-1 infection in comparison with uninfected individuals and the effect of HIV Nef protein on apoptotic body phagocytosis to determine if phagocytic activity is impaired by HIV infection. Monocytes/macrophages were isolated from 10 HIV-1-infected patients and from five healthy volunteers, whereas PMNL were isolated from healthy volunteers. Macrophage phagocytosis of apoptotic PMNL was determined by staining of apoptotic bodies with fluorescein-conjugated concanavalin A or with fluorescein-labeled phalloidin. Our data show significant impairment of PMNL apoptotic body macrophage phagocytosis in subjects with HIV-1 infection presenting a concentration of CD4(+) T lymphocytes of >200/mm(3) and in particular in those with <200 CD4(+) T lymphocyte cells/mm(3). In addition, HIV-1 recombinant Nef protein is able to decrease phagocytosis of apoptotic PMNL from normal human macrophages in a dose-dependent manner. The results of our study suggest that impaired macrophage phagocytosis of PMNL apoptotic bodies may contribute to the persistence of the inflammatory state in HIV-infected subjects, especially during opportunistic infections that are often favored by defective phagocytic activity.     

New biodefense strategies by neutrophils

Chemokines and other chemotactic factors induce neutrophils, macrophages, and dendritic cells to migrate to an inflammatory site and efficiently ingest and destroy infective microorganisms. Moreover, antigen-presenting cells, such as macrophages and dendritic cells, present the microbial antigens via major histocompatibility complex class II molecules, resulting in the activation of specific CD4 T cells. Since neutrophils have a short life-span and are highly susceptible to apoptosis, their role in antigen presentation has been questioned. However, various pro-inflammatory cytokines, such as interleukin (IL)-1, IL-6, tumor necrosis factor alpha, and interferon gamma, produced at the site of inflammation activate neutrophils and suppress apoptotic death. These cytokine-activated neutrophils show enhanced expression of cell surface molecules and become as competent as dendritic cells and macrophages in their ability of antigen presentation. Traditionally, neutrophils are known to be responsible for innate immunity, and recently they are also considered to be intimately associated with the establishment of acquired immunity. In the present review on the role of neutrophils we describe both classic innate and acquired immunity.     

HLA class II antigen presentation by melanoma

Constitutive expression of HLA II molecules is normally restricted to professional antigen presenting cells (APCs) of the immune system, although it also occurs in melanoma. Clinical evidence suggests that HLA II expression by melanoma is unfavorable, implicating a role for HLA II expression in the immunopathogenesis of the disease. As a first step, we asked whether human melanoma cells can process antigen or present peptide via HLA II molecules to a peptide specific CD4+ T cell clone. We compared the T cell response to melanoma vs. autologous B cells. In all cell lines tested, melanoma cells were able to process antigen and present peptide efficiently to CD4+ T cells, resulting in T cell proliferation increased 5 to 26 fold over no peptide controls. Blocking CD28 mediated signalling with CTLA-4lg had no effect on the T cell response to either melanoma or B cells. Blocking ICAM-1 resulted in a significant decrease in proliferation (>60%) in response to peptide presentation by melanoma but not B cells. These data demonstrate that (1) HLA II molecules on melanoma cells are functional and antigen processing pathways are intact, and (2) costimulatory signalling mediated via ICAM-1 but not B7 is important in the response of antigen experienced CD4+ T cells to HLA II mediated peptide presentation by melanoma.     

Immature dendritic cells reduce proinflammatory cytokine production by a coculture of macrophages and apoptotic cells in a cell-to-cell contact-dependent manner

We have demonstrated that phagocytosis of late apoptotic cells by mouse macrophages leads to the production of proinflammatory cytokines, notably macrophage-inflammatory protein (MIP-2), and therefore, a yet-unknown mechanism(s) should keep our body free of inflammation. In this study, we examined the effect of the addition of immature dendritic cells (iDCs) to a coculture of macrophages and apoptotic cells on MIP-2 production and phagocytosis by macrophages. The addition of iDCs to the coculture reduced MIP-2 production significantly but unexpectedly enhanced the phagocytosis by macrophages. Further study revealed that the reduction of MIP-2 production was dependent on cell-to-cell contact partly involving the beta(2) integrin family Mac-1. In addition, anti-inflammatory cytokines, interleukin-10 and transforming growth factor-beta, were involved in the reduction of MIP-2 production, as antibodies against these cytokines recovered MIP-2 production. Both cytokines were expressed by iDCs more significantly than macrophages at the mRNA levels, although they were hardly detected in the supernatant at the protein levels, suggesting that minute amounts of these anti-inflammatory cytokines were produced mainly by iDCs to block MIP-2 production in a cell-to-cell contact-dependent manner. Thus, this study reveals a new mechanism by which MIP-2 production by macrophages phagocytosing apoptotic cells is prevented.     

Role of antigen-presenting cells in long-term antitumor response based on tumor-derived apoptotic body vaccination.

Cellular therapy prospects for cancer are based on the development of T cell response, resulting in efficient tumor rejection and long-term protection. We have previously shown that treatment combining injection of interleukin-2 and tumor-derived apoptotic bodies, but not tumor cell extracts, permits to reject parental tumor in 40% of rats. We observed the implication of antigen-presenting cells (APCs) and tumor-derived apoptotic bodies in the rejection of established peritoneal carcinomatosis. We demonstrated that apoptotic bodies could be efficiently phagocytosed by monocytes, triggering them to an APC phenotype. When using these phagocytosing APCs, derived from peritoneal or blood monocytes, the remission rate reached 80% of rats. However, due to the lack of specific markers of rat monocyte-derived cells, the precise role of APCs, dendritic cells and/or macrophages responsible for this therapeutic improvement remained to be clarified. In order to elucidate this question, we developed an in vivo preventive cellular therapy based on tumor-derived apoptotic bodies, where macrophages were either depleted or activated. We report here that in a preventive antitumoral apoptotic body vaccination that allows survival for 40% of treated rats, the antitumor response was characterized by a specific long-term memory (cured rats rejected a second parental tumor cell challenge). Depletion of resident macrophages with silica or clodronate liposomes appeared to promote apoptotic body vaccination efficiency, increasing the treatment to 66% of success. In this case, FACS analysis showed that peritoneal cells present are essentially immature APCs and freshly recruited NK cells. In contrast, the onset of peritoneal inflammation by thioglycollate, inducing massive recruitment and activation of macrophages, reduced the overall survival, whatever the treatment was. Also, even though the surviving rate was better in silica-treated rats than control, no long-term protection was elicited. Our data suggest that massive inflammation, recruiting numerous activated macrophages, could inhibit tumor antigen presentation by 'professional' APCs having phagocytosed apoptotic bodies, and defavor a specific antitumoral T cell response. Although effective responses were developed against parental tumor cells with silica/apoptotic body treatment, they seemed only partial, limited to primary cytotoxic efficiency. In conclusion, even if macrophages did not appear necessary for a primary response to tumor cells, these cells seemed to be implicated in the establishment of memory and long-term antitumor response.     

CD31 promotes beta1 integrin-dependent engulfment of apoptotic Jurkat T lymphocytes opsonized for phagocytosis by fibronectin

Phagocyte integrins, by binding "bridging" molecules, mediate the ingestion of late apoptotic cells and apoptotic bodies by mechanisms that remain obscure. We recently reported that human monocyte-derived macrophages capture viable and apoptotic human leukocytes through homophilic interactions involving CD31 and that CD31 then promotes the engulfment of apoptotic cells or the detachment of viable cells. We now report that CD31 homophilic interactions between phagocyte and target cells lead to activation of phagocyte alpha5beta1 integrin and the engulfment of apoptotic Jurkat T lymphocytes via a fibronectin (Fn) "bridge." Although Fn and serum served as an opsonin for beta1 integrin-dependent phagocytosis of apoptotic leukemic T cells, they failed to do so for neutrophils. Given the complexities and inherent variability of working with primary cells, we have refined our model to show that ligation of CD31 on THP-1 macrophages also regulates beta1 integrin-dependent phagocytosis of Fn-coated Latex beads. Thus, selective "tethering" of apoptotic leukocytes by phagocyte CD31 not only discriminates dying from viable cells but also selectively activates phagocyte integrins for the engulfment of apoptotic cells.     

Impaired Macrophage Phagocytosis of Apoptotic Neutrophils in Patients with Human Immunodeficiency Virus Type 1 Infection

Dysfunction of neutrophils (polymorphonuclear leukocytes [PMNL]) and macrophagic cells occurs as a consequence of human immunodeficiency virus type 1 (HIV-1) infection. Macrophages contribute to the resolution of early inflammation ingesting PMNL apoptotic bodies. This study investigated macrophage ability to phagocytose PMNL apoptotic bodies in patients with HIV-1 infection in comparison with uninfected individuals and the effect of HIV Nef protein on apoptotic body phagocytosis to determine if phagocytic activity is impaired by HIV infection. Monocytes/macrophages were isolated from 10 HIV-1-infected patients and from five healthy volunteers, whereas PMNL were isolated from healthy volunteers. Macrophage phagocytosis of apoptotic PMNL was determined by staining of apoptotic bodies with fluorescein-conjugated concanavalin A or with fluorescein-labeled phalloidin. Our data show significant impairment of PMNL apoptotic body macrophage phagocytosis in subjects with HIV-1 infection presenting a concentration of CD4⁺ T lymphocytes of >200/mm³ and in particular in those with <200 CD4⁺ T lymphocyte cells/mm³. In addition, HIV-1 recombinant Nef protein is able to decrease phagocytosis of apoptotic PMNL from normal human macrophages in a dose-dependent manner. The results of our study suggest that impaired macrophage phagocytosis of PMNL apoptotic bodies may contribute to the persistence of the inflammatory state in HIV-infected subjects, especially during opportunistic infections that are often favored by defective phagocytic activity.     

Drebrin 1 in dendritic cells regulates phagocytosis and cell surface receptor expression through recycling for efficient antigen presentation

Phagocytosis, macropinocytosis and antigen presentation by dendritic cells (DC) requires reorganization of the actin cytoskeleton. Drebrin (Dbn1) is an actin binding and stabilizing protein with roles in endocytosis, formation of dendrite spines in neurons and coordinating cell–cell synapses in immune cells. However, its role in DC phagocytosis and antigen presentation is unknown. These studies now report that silencing of Dbn1 in DC resulted in restrained cell surface display of receptors, most notably MHC class I and II and co-stimulatory molecules. This, as expected, resulted in impaired antigen-specific T-cell activation and proliferation. Studies additionally revealed that knockdown of Dbn1 in DC impaired macropinocytosis and phagocytosis. However, there was a concomitant increase in fluid-phase uptake, suggesting that Dbn1 is responsible for the differential control of macropinocytosis versus micropinocytosis activities. Taken together, these findings now reveal that Dbn1 plays a major role in coordinating the actin cytoskeletal activities responsible for antigen presentation in DC.     

The human macrophage cell line U937 as an in vitro model for selective evaluation of mycobacterial antigen-specific cytotoxic T-cell function

Despite strong evidence for CD8+ T-cell function in murine mycobacterial infections, their corresponding role in human tuberculosis has proven more difficult to demonstrate. We have evaluated the human macrophage (Mphi) cell line U937 as an in vitro model for human leucocyte antigen (HLA) class I-restricted presentation of mycobacterial antigens, as HLA class I is constitutively expressed at high levels by U937 cells in the absence of detectable HLA class II or CD1 molecules. U937 cells were evaluated for their ability to phagocytose Mycobacterium tuberculosis and for their ability to present mycobacterial antigens to human HLA class I-matched cytotoxic T lymphocytes (CTLs). Differentiated U937 cells were capable of efficient phagocytosis of M. tuberculosis but did not generate a subsequent respiratory burst response, and were permissive for intracellular growth of both bacillus Calmette-Guérin (BCG) and the virulent M. tuberculosis H37Rv strain. CTL activity was restricted to live mycobacterial organisms and was shown to be mediated by M. tuberculosis-specific, HLA class I-matched, purified CD8+ CTL lines and CD8+ T-cell clones. Furthermore, M. tuberculosis-infected U937 targets were more rapidly and strongly lysed by CD8+ CTLs than were infected autologous Mphi. Finally, M. tuberculosis-infected U937 cells simultaneously provided a sensitive indicator for detection of mycobacterial-specific, HLA-unrestricted gammadelta+ CTL activity.     

Differential expression of major histocompatibility complex class Ia, Ib, and II molecules on monocytes-derived dendritic and macrophagic cells.

Blood monocyte derived antigen presenting cells (APC) such as dendritic cells and macrophages are considered as major promising tools for antitumoral immunotherapy. In order to contribute to their phenotype characterization, we have precisely investigated their levels of expression of MHC class Ia, Ib (HLA-G) and II molecules using mainly flow cytometry quantification assays. APC were generated from monocytes cultured for 7 days in the presence of GM-CSF and IL-4 or M-CSF. These cells, which exhibited known morphological and immunological features of dendritic cells and macrophages respectively, were evidenced to display high expression of MHC class Ia and class II antigens in comparison to that found in monocytes. Dendritic cells and macrophages thus expressed 2-fold more and 4-fold more MHC class Ia molecules and 5-fold and 3-fold more MHC class II DR molecules than parental monocytes. In addition, expression of MHC class II DP and DQ molecules, not or only barely detected in monocytes, was clearly demonstrated in the two kinds of APC. In contrast, monocytes, dendritic cells and macrophages failed to express MHC class Ib HLA-G antigen. The up-regulation in monocyte-derived APC of MHC class Ia and II molecules mediating the presentation of antigen peptides to lymphocytes fully supports the interest of such APC in antitumoral immunotherapy.     

对早期凋亡细胞的吞噬抑制T淋巴细胞活化的实验研究

目的:研究早期凋亡细胞及吞噬早期凋亡细胞的巨噬细胞对T淋巴细胞活化的影响。方法:体外以紫外线照射,诱导出早期凋亡的Jurkat细胞;建立早期凋亡细胞的吞噬模型;ELISA法分析早期凋亡细胞对LPS刺激下巨噬细胞分泌细胞因子的影响及在早期凋亡细胞和吞噬了早期凋亡细胞的巨噬细胞干预下,ConA刺激T淋巴细胞活化后CD69、CD25、CD71表达的变化。结果:巨噬细胞吞噬了早期凋亡细胞后,抑制性细胞因子(TGF_β1)的分泌明显上调,并且在一定程度上抑制了ConA刺激下的T淋巴细胞活化;具体表现为CD69、CD25、CD71等T淋巴细胞活化标志的表达受到明显抑制。当加入TGF_β1中和抗体后,这种抑制作用消失。结论:巨噬细胞吞噬了早期凋亡细胞后抑制ConA刺激下的T淋巴细胞CD69、CD25、CD71的表达,这种抑制作用依赖于的TGF_β1分泌增强。     

HLA class II signals sensitize B lymphocytes to apoptosis via Fas/CD95 by increasing FADD recruitment to activated Fas and activation of caspases

Human leukocyte antigen (HLA) class II heterodimers have a well defined role in peptide presentation to helper T lymphocytes. Moreover, engagement of HLA class II molecules leads to signal transduction in the antigen presenting cell. Signaling via HLA-DR increases CD95 mediated hypoploidy in B-cell blasts. Given the importance of CD95 for the homeostasis of lymphocyte populations, we examined the impact of the HLA-DR signal on the most proximal events in the CD95 apoptotic pathway. CD95 activation recruits the adapter molecule Fas-associated death domain protein (FADD) and thereby provides a scaffold for procaspase-8 activation. The HLA-DR signal increased both recruitment of FADD and activation of caspases-3 and -8 via CD95 activation. Sensitization was tightly controlled because neither FADD recruitment to CD95 nor caspase activation was induced via HLA-DR alone. In contrast, the HLA-DR signal and the CD95 signal both led to decreased mitochondrial membrane potential. Taken together, these data indicate that ligand interaction with HLA class II molecules preactivates the antigen presenting cell for death in the event of a subsequent interaction with the CD95 ligand. This would ensure termination of a specific immune response, particularly in cells with limited sensitivity to CD95 mediated apoptosis alone.     

Antigen presentation by a macrophage-like cell line persistently infected with respiratory syncytial virus

Severe infection by the human respiratory syncytial virus (RSV) early in life is associated with subsequent recurrent airway disease presumably mediated by dysregulation of the local immune response. Dysfunction of the immune response may be related to impaired macrophage functions. We have previously reported that RSV persistence in a macrophage culture (MPhiper) alters Fcgamma receptors (FcgammaR)-mediated phagocytosis and the production of pro-inflammatory cytokines. Here, we determined whether the ability of macrophages to process and present antigens and to stimulate RSV-specific CD8(+) T cells was altered in MPhiper. We also examined the level of expression of MHC class I molecules in MPhiper and the ability of these cells to present viral antigens to specific T lymphocytes. Our results showed that antigen processing and presentation were not altered by chronic RSV infection, and suggested that MPhiper were able to stimulate RSV-specific CD8(+) T lymphocytes.     

Lipopolysaccharide inhibits macrophage phagocytosis of apoptotic neutrophils by regulating the production of tumour necrosis factor α and growth arrest-specific gene 6

Removal of apoptotic cells from inflammatory sites by macrophages is an important step in the resolution of inflammation. However, the effect of inflammatory modulators on phagocytic clearance of apoptotic cells remains to be clarified. In this paper, we demonstrate that lipopolysaccharide (LPS), a potent inflammatory agent, inhibits the phagocytosis of apoptotic neutrophils by mouse peritoneal macrophages. This inhibition can be attributed to both LPS-mediated induction of tumour necrosis factor (TNF-α) and suppression of growth arrest-specific gene 6 (Gas6) in macrophages. We found that LPS-induced TNF-α production inhibited phagocytic ability of macrophages in an autocrine manner. In contrast, Gas6 expression in macrophages was blocked by LPS, which also contributes to the inhibition of macrophage phagocytosis by LPS. Our data suggest that phagocytic clearance of apoptotic neutrophils by macrophages can be regulated by local pro- and anti-inflammatory factors in two opposite states.