Macrophage Cell Line J774 Research Articles

Growth hormone and insulin-like growth factor-I increase macrophage uptake and degradation of low density lipoprotein

Hyperlipidemia has been reported in adults with hypopituitarism, and human (h) GH therapy has been shown to lower plasma cholesterol in patients with hypercholesterolemia. Macrophage cholesterol accumulation is an early event in atherosclerosis, and these cells have been shown to respond to GH and insulin-like growth factor (IGF-I). The present study was aimed at investigating the activity of GH and IGF-I in macrophages, and used murine macrophages as a model system to investigate the effects of GH and IGF-I on cellular uptake and metabolism of low density lipoprotein (LDL). The J-774 murine macrophage cell line was shown to bind hGH, to respond to hGH by an increase in cell IGF-I content, and to have specific high affinity binding sites for IGF-I. Mouse peritoneal macrophages and the J-774 macrophage cell line respond to hGH with a dose-dependent stimulation of cellular association and degradation of LDL as well as an enhanced cholesterol esterification rate. A similar response was observed after in vitro treatment of the cells with IGF-I. Preliminary results in human monocyte-derived macrophages showed similar results. The dependency of the effect of hGH on locally produced IGF-I was shown by abrogation of the hGH effect after adding anti-IGF-I antibody to the culture medium. It is concluded that murine macrophages possess the machinery to bind GH, produce IGF-I, and bind IGF-I. This machinery is used by macrophages, and apparently by other cells, to execute GH-dependent IGF-I-mediated stimulation of cellular uptake and metabolism of LDL. This may provide the explanation for both the elevated plasma LDL concentration in patients with GH deficiency and the effect of GH therapy to reduce plasma LDL levels.

Laminin enhances binding of Toxoplasma gondii tachyzoites to J774 murine macrophage cells.

We investigated the effects of the extracellular matrix proteins laminin and fibronectin on the attachment of tachyzoites of Toxoplasma gondii to the murine macrophage cell line J774. Laminin but not fibronectin increased parasite attachment to J774 cells in a dose-dependent fashion. Cyclic YIGSR, a laminin-derived peptide which inhibits laminin binding to the 32/67-kDa laminin-binding protein on host cells, blocked the laminin-mediated enhancement of parasite attachment. An antiserum to the 32/67-kDa laminin-binding protein also inhibited binding of parasites to J774 cells. These results, in conjunction with our previous observations (G. C. Furtado, F. L. Collins, and K. A. Joiner, submitted for publication), demonstrate that tachyzoites bearing surface laminin bind to multiple laminin receptors in attaching to different target cells.

L-arginine transport is increased in macrophages generating nitric oxide.

Transport of L-arginine and nitrite production were examined in the murine macrophage cell line J774. Bacterial lipopolysaccharide (LPS) induced a dose- and time-dependent stimulation of nitrite production, which was further increased in the presence of interferon-gamma. Nitrite synthesis was absolutely dependent on extracellular L-arginine and inhibited in the presence of L-lysine or L-ornithine. In unactivated J774 cells L-arginine transport was saturable, with an apparent Km of 0.14 +/- 0.04 mM and Vmax. of 15 +/- 2 nmol/h per 10(6) cells. LPS (1 microgram/ml) induced a time-dependent stimulation of L-arginine transport, and after 24 h the Vmax. increased to 34 +/- 2 nmol/h per 10(6) cells. These findings indicate that activation of J774 cells with LPS produces an increase in both L-arginine transport and nitrite synthesis. The elevated rate of L-arginine transport in activated J774 cells may provide a mechanism for sustained substrate supply during enhanced utilization of L-arginine for the generation of NO.

IpaB of Shigella flexneri causes entry into epithelial cells and escape from the phagocytic vacuole.

By creating mutations within the Shigella flexneri ipaB gene, we have demonstrated that the invasion of epithelial cells is a three-step process encompassing adhesion on the cell surface, entry and lysis of the phagocytic vacuole allowing subsequent access to the cytoplasm. SC403, an insertion mutant which lacks expression of IpaB but still expresses downstream genes, has been particularly studied. It is non-invasive, does not elicit actin polymerization, but binds to HeLa cells indicating that an adhesion step occurs immediately prior to the entry process. The consequence of the inactivation of ipaB on the intracellular behaviour of S.flexneri was investigated using the macrophage cell line J774. SC403 was unable to lyse the phagocytic vacuole; moreover, this strain did not display the contact mediated haemolytic activity characteristics of Shigella. In addition to being a major component of the invasion complex, IpaB acts as a membrane-lysing toxin enabling escape to the cytoplasmic compartment.

Effects of taxol on the macrophage function. Interactions with some immunological parameters.

The effects of Taxol on some immunological parameters were investigated, in vitro, in the murine macrophage cell line J774.1. Mitochondrial dehydrogenase activity and (3H) TdR incorporation were shown to be increased in Taxol treated cells. Likewise, Taxol induced TNF alpha secretion. But Taxol seemed to be a weak inducer of the two interleukins IL-1 and IL-2, since their detection occurred late in the cell culture supernatants.

Identification of a macrophage-binding determinant on lipophosphoglycan from Leishmania major promastigotes.

Leishmania are obligatory intracellular parasites in mammalian macrophages that gain entry by receptor-mediated phagocytosis. Their major cell surface glycoconjugate, lipophosphoglycan (LPG), has been implicated in this process. A monoclonal antibody specific for Leishmania major LPG (WIC 79.3), which has been shown to block promastigote attachment to macrophages, was used to identify a macrophage-binding determinant of LPG. WIC 79.3 bound exclusively to the phosphorylated repeats of LPG and not to the saccharide core or lipid anchor. Furthermore, the epitope recognized by WIC 79.3 mapped to the phosphorylated oligosaccharide P5b, PO4-6[Gal(beta 1-3)Gal(beta 1-3)Gal(beta 1-3)]Gal(beta 1-4)Man(alpha 1-, which is unique to the LPG of promastigotes of L.major. Phosphorylated oligosaccharides P3, PO4-6[Gal(beta 1-3)[Gal(beta 1-4) Man(alpha 1-, and P4b, PO4-6[Gal(beta 1-3)Gal(beta 1-3)] Gal(beta 1-4)Man(alpha 1-, were also recognized by WIC 79.3 but with considerably lower (approximately 100-fold) affinities. The phosphorylated oligosaccharide P5b inhibited attachment of promastigotes of L. major to the macrophage cell line J774 to the same degree as phosphoglycan (derived from LPG) and Fab fragments of WIC 79.3, suggesting that P5b is a site of L. major LPG that is recognized by macrophage receptor(s) and is an important determinant in the attachment of promastigotes to host macrophages and initiation of infection.

An 100-kDa arachidonate-mobilizing phospholipase A2 in mouse spleen and the macrophage cell line J774. Purification, substrate interaction and phosphorylation by protein kinase C.

A phospholipase A2 hydrolyzing arachidonic-acid-containing phospholipids has been purified 5600-fold from mouse spleen and to near homogeneity from the macrophage cell line J774. A molecular mass of 100 kDa for the enzyme was estimated by SDS/PAGE, while it migrated as a 70-kDa protein upon gel chromatography. The enzyme from both sources showed the same characteristics as that previously identified in murine peritoneal macrophages [Wijkander, J. & Sundler, R. (1989), FEBS Lett. 244, 51-56], i.e. it was totally dependent on Ca2+ with half-maximal activity at approximately 0.7 microM and hydrolyzed arachidonoyl phosphatidylcholine, phosphatidylethanolamine and phosphatidylinositol equally well. Also, the platelet-activating-factor precursor, 1-O-alkyl-2-arachidonoylglycerophosphocholine, was hydrolyzed to a similar extent. A preference for arachidonoylphosphatidylcholine over oleoylphosphatidylcholine was seen both with sonicated vesicles and labeled macrophage membranes as substrate. Ca(2+)-dependent interaction of the enzyme with sonicated vesicles composed of neutral phospholipids led to rapid initial hydrolysis, followed by loss of catalytic activity. Such inactivation did not occur with vesicles of pure anionic phospholipids, or with membranes prepared from macrophages. Phospholipase A2, purified from J774 cells, was rapidly phosphorylated by protein kinase C type-II, leading to incorporation of approximately 0.5 mol phosphate/mol enzyme.

Thermospray tandem mass spectrometric analysis of oxygen incorporation into citrulline by nitric oxide synthase

Citrulline is formed as a co-product in the biosynthesis of nitric oxide from L-arginine by the action of either constitutive or inducible nitric oxide synthase which is present in a variety of cells. We have previously shown that the oxygen atom incorporated into both nitric oxide and citrulline derives from molecular oxygen and not water. This paper describes the tandem mass spectrometric analysis of citrulline synthesized by the macrophage cell line J774 in the presence of native or guanidino-labelled arginine and air or isotopically enriched oxygen. The results confirm that oxygen is incorporated into the ureido position of citrulline.

An 100‐kDa arachidonate‐mobilizing phospholipase A2 in mouse spleen and the macrophage cell line J774

An 100‐kDa arachidonate‐mobilizing phospholipase A₂ in mouse spleen and the macrophage cell line J774

Constitutive and inducible nitric oxide synthases incorporate molecular oxygen into both nitric oxide and citrulline.

Nitric oxide (NO) is synthesized by a number of cells from a guanidino nitrogen atom of L-arginine by the action of either constitutive or inducible NO synthases, both of which form citrulline as a co-product. We have determined the source of the oxygen in both NO and in citrulline formed by the constitutive NO synthase from the vascular endothelium and brain and by the inducible NO synthase from the murine macrophage cell line J774. All these enzymes incorporate molecular oxygen both into NO and into citrulline. Furthermore, activated J774 cells form NO from omega-hydroxyl-L-arginine, confirming the proposal that this compound is an intermediate in the biosynthesis of NO.

Cells of the J774 macrophage cell line are primed for antibody-dependent cell-mediated cytotoxicity following exposure to γ-irradiation

Activation of macrophages (Mφ) for host defense against tumor cells follows a sequence of priming events followed by an initiating stimulus that results in production and release of cytotoxic molecules that mediate target cell killing. We have developed a model to study specific macrophage cytotoxicity in vitro utilizing a cultured murine Mφ cell line, J774. Specific cytotoxicity of cultured human gastrointestinal tumor cells is achieved in the presence of murine IgG2a monoclonal antibody (mAb) 17-1-A. The ability of these cells to mediate antibody-dependent cell-mediated cytotoxicity (ADCC) is greatly enhanced following γ-irradiation. ADCC can be demonstrated at mAb 17-1-A concentrations ⩾ 1 μg/ml and effector/target cell ratios ⩾2. Exposure to doses ⩾ 10 Gy of γ-irradiation increases ADCC threefold. Varying the duration form J774 Mφ exposure to γ-irradiation until addition of antibody-coated target cells showed that the primed state for ADCC is stable for at least 8 days but approximately 24 hr is required for complete development of the primed state. mAb-dependent target cell death begins 8 hr after addition of mAb and labeled target cells to primed effector cells and is complete by 24 hr. Incubation of unirradiated J774 Mφ effector cells with recombinant murine interferon-γ (rmIFN-γ) also results in enhanced ADCC, but the extent of target cell killing achieved is less than that following priming by γ-irradiation. Concomitant priming of γ-irradiated J774 Mφ with rmIFN-γ increases the extent of ADCC. Further study of irradiated J774 cells may elucidate the molecular pathways utilized by Mφ for achieving and maintaining the primed state for ADCC. Irradiated J774 cells will also provide a homogenous, stably primed cell type in which to examine the mechanism(s) of cytotoxicity employed by tumoricidal Mφ.

Chinese Medicinal Herbs Reverse Macrophage Suppression Induced by Urological Tumors

Tumors are known to produce factors suppressing macrophage function. In this study we demonstrated in vitro suppression of macrophage chemiluminescent oxidative burst associated with viable cells and cell-free extracts of two urological neoplasms—murine renal cell carcinoma (Renca) and murine bladder tumor (MBT). Suppression was reversed by extracts of two Chinese medicinal herbs, Astragalus membranaceus (AM) and Ligustrum lucidum (LL). Murine macrophage cell line J774 was incubated with either the viable tumor cells or the cell-free tumor extract for 18 hours at 37C and 5% CO2. Chemiluminescent oxidative burst as an indicator of macrophage function was triggered by adding zymosan A suspension containing luminol and assayed in an automated luminometer. Photon emission over time was counted and the results were expressed as integrated photon emission. Significant dose-related depression of oxidative burst occurred with either the viable tumor cells or the cell-free tumor extracts. Depression was partially or completely reversed by the presence of 50-100 μg./ml. of either the AM or the LL extract. AM and LL have previously been shown to modulate immune response. Data from this study suggest that they may also exert their antitumor activity via abolition of tumor-associated macrophage suppression.

Platelet secreted lipoprotein-like particle is taken up by the macrophage scavenger receptor and enhances cellular cholesterol accumulation

Enhanced macrophage cholesterol accumulation is associated with foam cell formation in the atherosclerotic lesion. Since platelet activation plays an important role in atherogenesis, we questioned whether products released from activated platelets could affect macrophage cholesterol metabolism. The addition of platelet-conditioned medium (PCM, obtained from collagen activated platelets) to a J-774 macrophage cell line, enhanced cellular cholesteryl ester content by 32%. The cholesterol esterification rate was also increased by 29%. Pre-loading the macrophages with cholesterol by incubation with acetyl-LDL, resulted in a further elevation of 48% in PCM-mediated cholesterol esterification. Possible mechanisms for the enhanced cholesterol esterification by J-774 macrophages following incubation with PCM include increased cholesterol influx and/or decreased cholesterol efflux (These cells were recently shown not to synthesize cholesterol). However, both increased uptake of PCM cholesterol by the macrophages as well as increased cellular cholesterol efflux (by 22%) were noted. The enhancement of cholesterol esterification by PCM was competitively inhibited by fucoidin and polyinosinic acid, implicating PCM binding to the scavenger receptor. This was further evidenced by the observations that apolipoprotein E which reduces cellular uptake via the scavenger receptor but not via the LDL receptor, also inhibited the effect of PCM, whereas IgG C-7, the LDL receptor antibody, did not alter the effect of PCM. Lysosomal involvement in the cellular processing of PCM was observed since PCM activity was inhibited by the lysosomal inhibitor, chloroquine. Partial purification of PCM by gel filtration revealed that the cholesterol component was associated with both phospholipids and proteins in a lipoprotein-like particle. Delipidation of PCM resulted in its inactivation but both heat treatment and tryptic digestion of PCM, revealed that the protein (and not only the cholesterol) component was also essential for the effect of PCM on cellular cholesterol esterification. Furthermore, PCM prepared from platelets of a patient with Gray Platelet Syndrome that lack platelet alfa granules (which contain platelet specific proteins), failed to enhance cholesterol esterification. These results demonstrate that lipoprotein-like particles released during platelet activation can interact with the macrophage scavenger receptor thus leading to enhanced cellular cholesterol accumulation.

Extracellular and intracellular activities of clarithromycin used alone and in association with ethambutol and rifampin against Mycobacterium avium complex

Mycobacterium avium complex bacteria are opportunistic human pathogens, and their chemotherapy remains a challenge since these organisms are resistant to a majority of routine antituberculous drugs. Recently, a wide range of new macrolide antibiotics has been developed, among which the drug clarithromycin appears to have a selective action against M. avium bacteria. In the present study, we have investigated the action of clarithromycin alone (MIC and MBC determinations) and in association with the routine antimycobacterial drugs ethambutol and rifampin at sublethal concentrations (1 micrograms/ml; below concentrations obtainable in human serum) against M. avium. Our viable count data showed that clarithromycin was bactericidal against all 10 strains of M. avium studied and that its activity was enhanced by ethambutol (in 8 of 9 strains) and rifampin (in 3 of 9 strains). The use of all three drugs in association resulted in higher bactericidal effects than found with any of the drugs used alone or in two-drug combinations in seven of nine strains. The bactericidal effects of various drugs used alone and in combination at concentrations obtainable in human serum were investigated against the type strain ATCC 15769 by using 7H9 broth and BACTEC radiometry (extracellular action) and a J-774 macrophage cell line (intracellular action). A good agreement between the extracellular and intracellular activities was found. Electron microscopy using a ruthenium red cytochemical staining of the bacteria showed that clarithromycin disorganized the outer wall layer and the cytoplasmic membrane in the mycobacterial cell envelope and resulted in formation of large vacuoles inside the cytoplasm, with solubilization of ribosomal structures and consequent plasmolysis. Its association with ethambutol and rifampin resulted in more drastic alterations in the bacterial morphology than were seen with any of the drugs used alone, leading to the removal of the bacterial outer layer, homogenization of cytoplasm, complete cell lysis, and formation of ghosts.

Cholesterol accumulation in J774 macrophages induced by triglyceride-rich lipoproteins. Comparison of very low density lipoprotein from subjects with type III, IV, and V hyperlipoproteinemias.

The capacity of human triglyceride-rich lipoproteins to induce cholesterol accumulation in the murine J774 macrophage cell line was investigated with large very low density lipoprotein (VLDL, Sf 60-400) obtained from subjects with type III, IV, and V hyperlipoproteinemias. After incubation for 24 hours, VLDLs from type IV and type V subjects were similar in their ability to raise cellular cholesterol deposition threefold to fourfold and cellular triglyceride 16-fold. The increase in cholesterol was entirely due to the dramatic increase in cholesterol ester, from less than 1 to greater than 50 micrograms/mg cell protein. Total cholesterol accumulation was fourfold to fivefold greater than the cholesterol accumulation observed for VLDL or low density lipoprotein (LDL) from normal subjects. Cholesterol esterification (acyl coenzyme A: cholesterol acyltransferase [ACAT] activity) paralleled the rate of cholesterol accumulation in these cells. Treating the macrophages with the ACAT inhibitor 58035, which is known to downregulate the LDL receptor in these cells, diminished cholesterol accumulation by 40% for type IV VLDL and by 23% for normal LDL. Since hypertriglyceridemic VLDL carries excess apoprotein (apo) E molecules, we investigated the role of normal and abnormal apo E. An anti-apo E monoclonal antibody, known to block the binding of apo E to the LDL receptor, blocked type IV VLDL-induced cholesterol ester accumulation by approximately 70%. In contrast to type IV subjects, VLDL from type III subjects (homozygous for apo E2) when incubated with J774 macrophages (which do not secrete apo E) caused only a modest 1.5-2-fold increase in cellular cholesterol. Pre-beta- and beta-migrating VLDL subfractions from type III subjects were equally ineffective in causing cholesterol accumulation. By contrast, beta-VLDL from cholesterol-fed rabbits caused a sevenfold to eightfold increase in cellular cholesterol content. These results indicate that triglyceride-rich lipoproteins from type IV and type V subjects can cause substantial cholesterol ester accumulation and enhanced cholesterol esterification in J774 cells. The lower cholesterol accumulation with type IV VLDL in the presence of apo E antibodies and VLDL from type III subjects demonstrates the importance of functional apo E in this process.

Glucocorticoids inhibit the induction of nitric oxide synthase in macrophages

The effect of glucocorticoids on the production of NO 2 − and NO by the macrophage cell line J774 was investigated. Stimulation of the cells with lipopolysaccharide (LPS) resulted in a time-dependent accumulation of NO 2 − in the medium, reaching a plateau after 48h. Concomitant incubation of the cells for 24h with dexamethasone (0.001–1.0 μM) or hydrocortisone (0.01–10.0 μM) caused a concentration-dependent inhibition of NO 2 − formation. The cytosol of J774 cells stimulated with LPS and IFN-γ produced a time-dependent increase in the release of NO. This was blocked in a concentration-dependent manner by dexamethasone and hydrocortisone, but not progesterone, administered concomitantly with the immunological stimulus. None of these compounds had any effect on the release of NO once the enzyme had been induced. The inhibitory effect of hydrocortisone on NO formation was blocked by cortexolone. These data suggest that part of the anti-inflammatory and immunosuppressive actions of glucocorticoids is due to their inhibition of the induction of the NO synthase.

Intracellular Bactericidal Activity of Ciprofloxacin and Ofloxacin Against Mycobacterium tuberculosis H 37Rv Multiplying in the J-774 Macrophage Cell Line

Among new fluoroquinolone derivatives, the N-cyclopropylanalogs Ciprofloxacin (CIPRO) and ofloxacin (OFLO) have recently been found to have a high in vitro activity against a variety of mycobacteria (2). In this study, we have investigated their action against intracellularly growing Mycobacterium tuberculosis. For this purpose, the J-774 macrophage cell line was infected with the H37Rv type strain of M. tuberculosis, and drugs (at their serum level concentrations obtainable in healthy individuals (= 5 [µg/ml; 8) were added after 2 days of intracellular growth of the bacteria. The bacterial growth during the experimentation was followed both electron microscopically and also by lysing the macrophages at various time intervals, and enumerating the bacterial viable counts after plating the lysate on appropriate media. Both drugs at the concentrations used did not affect macrophage viability (as assessed by trypan blue staining), and were highly bactericidal against the virulent tubercle bacilli multiplying in our J-774 macrophage model.

Chelation of cytoplasmic Ca2+ increases plasma membrane permeability in murine macrophages.

Cytoplasmic free Ca2+ (Ca2+i) was chelated to 10-20 nM in the macrophage cell line J774 either by incubation with quin2 acetoxymethyl ester in the absence of external Ca2+ (Di Virgilio, F., Lew, P.D., and Pozzan, T. (1984) Nature 310, 691-693) or by loading [ethyl-enebis(oxyethylenenitrilo)]tetraacetic acid (EGTA) into the cytoplasm via reversible permeabilization of the plasma membrane with extracellular ATP (Steinberg, T.H., Newman, A.S., Swanson, J.A., and Silverstein, SS.C. (1987) J. Biol. Chem. 262, 8884-8888; Di Virgilio, F., Meyer, B.C., Greenberg, S., and Silverstein, S.C. (1988) J. Cell Biol. 106, 657-666). After removal of ATP from the incubation medium, ATP-permeabilized Ca2+i-depleted macrophages recovered a near-normal plasma membrane potential which slowly depolarized over a 2-4 h incubation at low [Ca2+]i. In both ATP-treated and quin2-loaded cells, depolarization of plasma membrane potential was paralleled by an increase in plasma membrane permeability to low molecular weight aqueous solutes such as eosin yellowish (Mr 692), ethidium bromide (Mr 394), and lucifer yellow (Mr 463). This increased plasma membrane permeability was not accompanied by release of the cytoplasmic marker lactic dehydrogenase for incubations up to 4 h and was likely a specific effect of Ca2+i depletion since it was not caused by: (i) the mere incubation of macrophages with extracellular EGTA, i.e. at near-normal [Ca2+]i; and (ii) loading into the cytoplasm of diethylenetriaminepentaacetic acid, a specific chelator of heavy metals with low affinity for Ca2+. Treatment of Ca2+i-depleted cells with direct (phorbol 12-myristate 13-acetate) or indirect (platelet-activating factor) activators of protein kinase C prevented the increase in plasma membrane permeability. Down-regulation of protein kinase C rendered Ca2+i-depleted macrophages refractory to the protective effect of phorbol 12-myristate 13-acetate. This report suggests a role for Ca2+i and possibly protein kinase C in the regulation of plasma membrane permeability to low molecular weight aqueous solutes.

Scavenger receptor-mediated uptake and metabolism of lipid vesicles containing acidic phospholipids by mouse peritoneal macrophages.

We studied the mechanism of uptake and metabolism of exogenous phospholipids in mouse peritoneal macrophages using vesicles composed of various phospholipids and cholesterol. Macrophages in culture were found to actively incorporate and metabolize phosphatidylcholine/cholesterol vesicles containing small amounts of acidic phospholipids such as phosphatidylserine, phosphatidylinositol, or phosphatidic acid and to store the fatty acyl chains and cholesterol in triacylglycerol and cholesteryl ester form in their cytosol. These cells exhibited massive amounts of oil red O-positive lipid droplets, a typical feature of foam cells. The metabolism of exogenous phospholipid vesicles was completely inhibited by chloroquine and cytochalasin B, suggesting that vesicle uptake occurs by endocytosis. A similar type of metabolism was observed in guinea pig peritoneal macrophages, macrophage cell line J774.1, but not in Swiss 3T3 fibroblasts. Competition studies using various ligands for the scavenger receptor showed that acetylated low density lipoprotein (acetyl-LDL), dextran sulfate, or fucoidan was able to compete for up to 60% of the binding of phosphatidylserine-containing vesicles, and that copper-oxidized LDL (oxidized LDL) competed for more than 90% of the vesicle binding. On the other hand, phosphatidylserine-containing vesicles was able to compete for more than 90% of the binding of acetyl-LDL. These results indicate that acidic phospholipids are recognized by the scavenger receptors on the surface of macrophages and that more than one scavenger receptor exists on mouse peritoneal macrophages, i.e. one capable of recognizing acetyl-LDL, oxidized LDL, and an array of acidic phospholipids on membranes, and the other recognizing both acidic phospholipids and oxidized LDL but not acetyl-LDL.

Invasion and replication of Salmonella typhimurium in animal cells

A total of 81 avirulent Tn10 insertion mutants of Salmonella typhimurium have previously been described. These mutants were selected for the inability to survive in murine macrophages. We have characterized the abilities of the most avirulent of these mutants to adhere to, invade, and replicate in both macrophages and nonphagocytic epithelial cells. The results suggest that most mutants contain a defect that is specific to survival within professional phagocytes. These mutants invaded and replicated normally within nonphagocytic human colon adenocarcinoma cells (Caco-2) but did not survive in the macrophage cell line J774. One mutant invaded both macrophages and epithelial cells much less efficiently than the parental strain. The defect associated with this mutant appears to be a result of decreased adherence to animal cells.