Macrophage progenitor cell and colony-stimulating factor production during granulomatous schistosomiasis mansoni in mice.

Schistosoma mansoni worm eggs stimulate a T-cell-mediated granulomatous response in which macrophages play important inflammatory and regulatory roles. Although much has been learned about the functions of the schistosome granuloma macrophages, their origin and replicative ability are unknown. In the present sequential study, macrophage progenitor cells in the bone marrow (GM-CFC) and liver granulomas (M-CFC) were enumerated, and macrophage colony-stimulating factor (CSF-1) in the circulation and culture fluid of explanted granulomas of infected mice was assayed. During the acute phase of the infection, when the granulomatous response was vigorous (weeks 8 to 12) GM-CFC numbers were high in the bone marrow and M-CFC numbers were low within granulomas. Circulating CSF-1 levels were elevated, but the vigorous granuloma-secreted CSF-1 level was low. During the chronic phase of the infection, the number of GM-CFC within the bone marrow and levels of circulating CSF-1 returned to normal. Conversely, a sharp increase in the number of M-CFC occurred within the small immunomodulated granulomas that also secreted high levels of CSF-1. The frequency of M-CFC that proliferated under exogenously added CSF-1 within the immunomodulated granulomas was significantly higher than that of cells in the vigorous granulomas. Adherent macrophage-rich cells obtained after dispersal of the granulomas appeared to be one source of CSF-1 production. These data indicate that during the infection the macrophage supply to and replicative ability within the granulomas is influenced by systemically and/or locally produced CSF-1.     

Specific and natural antibody production during Salmonella typhimurium infection in genetically susceptible and resistant mice.

Genetically susceptible (C57BL/6) and resistant (CBA) mice were infected with an avirulent strain of Salmonella typhimurium and studied over a 35-day period for the production of antibodies directed against bacterial antigens including lipopolysaccharide (LPS) (specific antibodies) and antibodies directed against self antigens [natural antibodies (NAb)]. Antibodies directed against LPS and self antigens were detected by enzyme immunoassay (EIA) and those directed against other bacterial antigens by immunoblotting. We found that serum natural antibody titres in C57BL/6 and CBA mice were similar and correlated with the bacterial load in the spleen and liver. In C57BL/6 mice, anti-LPS antibodies remained polyreactive and of the IgM isotype. In contrast, CBA mice, after an early increase in polyreactive IgM anti-LPS antibodies, mounted a specific anti-LPS IgG antibody response. The immunoblotting results demonstrated that the IgM polyreactive antibodies in the resistant and susceptible mice recognized bacterial antigens of different molecular weights and that CBA, but not C57BL/6 mice, were able to produce IgG antibodies recognizing bacterial components. Our results suggest that the synthesis of antibodies directed against bacterial antigens and natural antibodies follow, at least partially, distinct pathways, but they do not allow us to determine whether these two antibody populations are produced by the same or distinct B-cell subpopulations.     

Effect of murine cytomegalovirus infection on mitogen responses in genetically resistant and susceptible mice.

Temperature-sensitive (ts) reassortant vaccine strains derived from the A/Udorn/72 ts-1A2 donor virus were not sufficiently stable genetically in humans. We therefore sought to produce a new, more stable donor virus. We had previously identified a stable ts virus with a ts P3 gene and in the current study identified another relatively stable single-lesion ts virus with a ts mutation in the NP gene. A new ts reassortant virus was constructed by mating these two single mutants and by isolating three reassortant progeny, clones 20, 53, and 55, that contained both a ts P3 and a ts NP gene. These reassortant progeny possessed a 37 to 38°C shutoff temperature and were as restricted in their replication in hamster lungs as the A/Udorn/72 ts-1A2 virus. All isolates from the lungs and nasal turbinates of hamsters were temperature sensitive. An in vitro stress test was used to determine whether the new ts P3 ts NP reassortant virus would undergo loss of its ts phenotype after replication at semipermissive temperature. Clone 20 and 55 reassortants underwent progressive loss of their ts phenotype in vitro, although at a rate slightly less than that of the A/Udorn/72 ts-1A2 virus. The level of genetic stability after replication in vivo was assessed in cyclophosphamide-treated hamsters in which virus replication continued for up to 15 days. Again, both the A/Udorn/72 ts-1A2 and the new ts P3 ts NP reassortant clone 55 manifested a progressive loss of temperature sensitivity after 7 days of replication. Clone 55 virus lost temperature sensitivity significantly less rapidly than the A/Udorn/72 ts-1A2 virus. These results indicated that, although the new ts P3 ts NP reassortant virus was more stable than the A/Udorn/72 ts-1A2 virus, it nevertheless underwent progressive loss of temperature sensitivity after replication in vitro and in vivo. Therefore, it does not appear to be a satisfactory donor virus. This experience plus that gained earlier with other ts mutants of influenza A virus suggest that influenza A virus mutants that rely solely upon their ts phenotype for attenuation are unlikely to exhibit the phenotypic stability required of a vaccine virus. Other genetic techniques are needed to produce more stable influenza A virus strains.     

Differential production of granulocyte-macrophage colony-stimulating factor by macrophages from mice susceptible and resistant to Leishmania mexicana amazonensis.

The present results demonstrate that macrophages from mice susceptible to infection with Leishmania mexicana amazonensis sustain a higher production of granulocyte-macrophage colony-stimulating factor (GM-CSF) throughout the in vitro infection than macrophages from a resistant strain. Resident macrophages from BALB/c and C57B1/10 mice were infected with promastigotes of L. mexicana amazonensis and the amount of biologically active GM-CSF was measured in the supernatants collected at different times of infection. Measurements were made by bone marrow and GM-CSF/interleukin-3 addicted cell proliferation. Because GM-CSF is a disease-exacerbating cytokine, its differential production by infected macrophages may be one of the mechanisms defining resistance or susceptibility to a leishmanial infection.     

Sendai virus infection in genetically resistant and susceptible mice.

The pathogenesis of Sendai virus infection in genetically resistant (C57Bl/6) and susceptible (DBA/2) nonimmune adult mice was investigated. Rising serum complement-fixation (CF) antibody titers were delayed in DBA/2 mice as compared with C57Bl/6 mice. C57Bl/6 mice developed descending desquamative endobronchiolitis, and DBA/2 mice developed descending proliferative endobronchiolitis and bronchogenic alveolitis. Peribronchiolar lymphoid cuffs that formed in C57Bl/6 mice were thicker and more densely populated than those of DBA/2 mice. Immunofluorescence demonstrated viral antigens confined to the epithelial lining of conducting airways in C57Bl/6 mice but extending to alveolar corner cells in DBA/2 mice. Studies with a transmission electron microscope confirmed that Type II pneumocytes were infected only in DBA/2 mice. IgG-containing cells selectively accumulated along the airways of both strains, but fewer were recruited by DBA/2 mice. These results suggest that genetic resistance to Sendai virus is expressed through the immune system.     

A sandwich enzyme-linked immunoadsorbent assay for detection of murine macrophage colony-stimulating factor (CSF-1)

A simple three-layer sandwich enzyme-linked immunoadsorbent assay (sandwich-ELISA) has been developed for murine macrophage colony-stimulating factor-1 (CSF-1) using the two monoclonal antibodies on which we recently reported (J. Immunol. (1988) 141, 483). The anti-CSF-1 monoclonal antibodies used in this assay recognize different epitopes of the same antigen, thereby permitting the detection of low amounts of CSF-1. This assay is specific to murine CSF-1. Recombinant human macrophage colony-stimulating factor, murine GM-CSF, or IL-3, either alone or together with CSF-1, does not interfere with the assay. The advantage of this assay over other reported immunoassays for CSF-1 is that radiolabeled or large quantities of purified CSF-1 are not required. This sandwich-ELISA compares favorably with other assays in its rapidity, simplicity, and sensitivity.     

Experimental ocular toxoplasmosis in genetically susceptible and resistant mice

Genetic factors determining the pathogenesis and course of ocular toxoplasmosis are poorly understood. In this study, we explored the development of experimental ocular pathogenesis in genetically dissimilar mice infected with either the RH strain, the PLK strain, or the immunodominant surface antigen 1 (SAG1 [P30])-deficient mutant of the RH strain of Toxoplasma gondii. At 11 days postinfection, ocular infection of C57BL/6 mice with all of the strains of parasites resulted in severe inflammatory lesions and high numbers of parasites in eye tissue; less severe ocular lesions at earlier histopathology and prolonged survival were observed in this mouse strain infected with either the major surface antigen 1-deficient SAG1(-/-) strain or the less virulent PLK strain compared with RH infection. In contrast, both BALB/c and CBA/J mice had less severe lesions and low numbers of parasites in their eye tissue, and infection developed into the chronic stage in these mice. There were significantly higher serum levels of gamma interferon and tumor necrosis factor alpha in C57BL/6 mice than in BALB/c and CBA/J mice following ocular infection. These observations confirm earlier reports on systemic immunity to these parasites that the route of Toxoplasma infection markedly influences survival of mice. Our data indicate that genetic factors of the host as well as the parasite strain are critical in determining susceptibility to experimental ocular toxoplasmosis in murine models.     

Resistance and susceptibility of mice to bacterial infection: course of listeriosis in resistant or susceptible mice.

Within 3 h after oral challenge of mice with Salmonella typhimurium, foci of infection developed in the Peyer's patches of the small intestine. The numbers of organisms in the cecum, although in excess of those found in the small intestine, were not firmly associated with the cecal wall but were present largely in the cecum's contents. The Peyer's patches at first were remarkably incapable of eliminating even small numbers of Salmonella, but at about 7 days after infection developed the ability to eliminate a less virulent strain of S. typhimurium. Selected strains of Salmonella of varied virulence, and hybrid Escherichia coli/Salmonella typhimurium with varied O-antigens, revealed that those of low virulence could multiply within the intestinal Peyer's patches at nearly the same rate as a virulent strain, and the ability to multiply within the Peyer's patches was not dependent upon O-antigen type or smooth lipopolysaccharide. The ability of these strains to adhere to intestinal mucosa in vitro did not reflect on their ability to colonize the Peyer's patches, although strains of high in vitro adhesive ability appeared in greater numbers initially after oral challenge. Anti-O serum, ineffective in reducing the in vitro adhesive ability of virulent S. typhimurium, when given with the oral challenge prevented Peyer's patch colonization but was unable to prevent the appearance of a systemic infection. Anti-H serum, although effective in vitro in preventing adherence, had no effect in vivo. These experiments suggest that adhesiveness is neither essential nor sufficient for the virulence of Salmonella and that the usual development of a systemic infection after colonization of the small intestinal Peyer's patches may be subverted by the presence of O-antibody.     

Listeria antigen-binding cells in the spleens of normal and immunized mice resistant or susceptible to listeriosis

Normal mice of the Listeria-resistant C57Bl/6 strain contain in their spleens a higher number of cells that bind Listeria monocytogenes cell wall fraction antigen (LmA) than normal DBA/2 mice, which are more susceptible to infection. LmA-binding cells are probably B cells, nylon-wool adherent, and inhibited by anti-mouse immunoglobulin antibody but not sensitive to the action of monoclonal anti-mouse macrophage and anti-Thy.1.2 antibody. A single intraperitoneal injection of 10(8) Listeria monocytogenes causes a rapid increase in the number of LmA-binding cells in the spleens of C57Bl/6 mice, and this can be seen as early as 24 h. On the other hand, in DBA/2 mice an increase in these cells becomes evident only by the 4th day. Moreover, the increment in the number of LmA-binding cells in C57Bl/6 mice is more marked than in DBA/2 mice.     

Dissemination and proliferation of Salmonella typhimurium in genetically resistant and susceptible mice.

Genetically resistant A/J and CBA mice were inoculated intraperitoneally with either 10(3) or 10(4) organisms of a virulent strain of Salmonella typhimurium; susceptible C57BL/6J and BALB/c mice were inoculated with either 10(2) or 10(3) organisms. Except with the smaller dose in resistant mice, fatal infection ensued. Bacteraemia occurred within 1 h after inoculation, except that it was not detectable during the first 6 h in the susceptible mice inoculated with 10(2) organisms. From day 2, the circulating bacterial population continued to increase in all infected mice, except that it remained under control in the resistant mice inoculated with the lower dose (10(3) organisms). The pathogen proliferated logarithmically in the liver from day 2, and a bacterial count of c. 10(8) cfu/g of tissue was reached when the animals died at 5-7 days; again, the resistant mice inoculated with 10(3) organisms were an exception in which the hepatic bacterial population was kept under control and the mice survived.     

Comparative antibody response to Salmonella antigens in genetically resistant and susceptible mice.

The ELISA was used to titrate the antibody response in mice inoculated with salmonella antigens. The genetically resistant A/J and susceptible C57BL/6J mice were either infected with the virulent or the avirulent Salmonella typhimurium. Alternatively, they were inoculated either once or twice with the heat-killed salmonella vaccine. No appreciable difference could be detected in the relative ability of these two strains of mice to produce antibodies against the lipopolysaccharide antigens of this pathogen under these four conditions.     

Macrophage colony-stimulating factor in murine candidiasis: serum and tissue levels during infection and protective effect of exogenous administration.

Serum and tissue concentrations of the macrophage-specific colony-stimulating factor (CSF-1) and the number of CSF-1-responsive cells in bone marrow were investigated in mice chronically infected with a low-virulence strain of the opportunistic zoopathogenic yeast Candida albicans. CSF-1 levels in serum, brain, kidney, liver, and lung were significantly increased shortly after infection and remained elevated during the 2 weeks preceding the onset of specific T cell-dependent immunity. The number of monocytic precursor cells was also increased in the bone marrow of infected mice. When macrophages from naive donors were exposed in vitro to purified murine CSF-1, their anticandidal activity in vitro appeared to be enhanced. CSF-1 was also administered in vivo to prospective recipients of a lethal C. albicans challenge. The results showed that the factor could effectively potentiate the animals' resistance to the yeast, as shown by increased survival times and reduced recovery of viable C. albicans from the organs of the CSF-1-treated mice. Therefore, the present data suggest that CSF-1 is likely to contribute to early resistance to fungal infection and could be successfully exploited in experimental models of antifungal immunotherapy.     

Neutrophil responses to Mycobacterium tuberculosis infection in genetically susceptible and resistant mice

The role of neutrophils in tuberculosis (TB) resistance and pathology is poorly understood. Neutrophil reactions are meant to target the offending pathogen but may lead to destruction of the host lung tissue, making the defending cells an enemy. Here, we show that mice of the I/St strain which are genetically susceptible to TB show an unusually high and prolonged neutrophil accumulation in their lungs after intratracheal infection. Compared to neutrophils from more resistant A/Sn mice, I/St neutrophils display an increased mobility and tissue influx, prolonged lifespan, low expression of the CD95 (Fas) apoptotic receptor, relative resistance to apoptosis, and an increased phagocytic capacity for mycobacteria. Segregation genetic analysis in (I/St x A/Sn)F2 hybrids indicates that the alleles of I/St origin at the chromosome 3 and 17 quantitative trait loci which are involved in the control of TB severity also determine a high level of neutrophil influx. These features, along with the poor ability of neutrophils to restrict mycobacterial growth compared to that of lung macrophages, indicate that the prevalence of neutrophils in TB inflammation contributes to the development of pathology, rather than protection of the host, and that neutrophils may play the role of a "Trojan horse" for mycobacteria.     

Lung cell responses to M. tuberculosis in genetically susceptible and resistant mice following intratracheal challenge

One approach to study the role of distinct cellular mechanisms in susceptibility/resistance to tuberculosis (TB) is to compare parameters of response to infection in the lungs of mouse strains exhibiting genetically determined differences in TB susceptibility/severity. Interstrain differences in antimycobacterial macrophage reactions, T cell responses & inflammation in the lungs of TB-susceptible I/St, TB-resistant A/Sn and (I/St x A/Sn)F1 mice were analysed following intratracheal inoculation of 103 CFUs of M. tuberculosis H37Rv. The antimycobacterial responses in the lungs of susceptible I/St mice were characterized by: (i) increased inflammatory infiltration by all major immune cell subsets; (ii) decreased type 1 cytokine production; (iii) impaired antimycobacterial activity of lung macrophages; (iv) unusually high proliferation of lung T lymphocytes. Differences in several parameters of anti-TB immunity between susceptible and resistant mice corresponded well to the polygenic pattern of TB control previously established in this mouse model. Importantly, lung macrophages isolated from noninfected mice were unable to respond to IFN-gamma by increasing their mycobactericidal function, but between weeks 3 and 5 of the infection this capacity developed in all mice. However, by this time point susceptible but not resistant mice demonstrated a pronounced decrease in IFN-gamma production by lung cells. This chain of events may explain the inability of I/St mice to control both early and chronic TB infection.     

Interleukin-1 and interleukin-2 production in resistant and susceptible inbred mice infected with Trypanosoma congolense.

Human adherent cells, obtained by EDTA reversible adherence to plastic, are potent effectors in cell-mediated cytotoxicity. Spontaneous cytotoxicity in a 2-hr assay against K562 target cells was shown to be largely mediated by contaminating natural killer (NK) cells. Treatment of adherent cells with NK-specific monoclonal antibody anti-Leu-11 plus complement abolished almost completely the spontaneous cytotoxicity. Spontaneous cytotoxicity by adherent cells was also reduced when the phorbol ester PMA was present in the assay. On the other hand, PMA induced a cytotoxic response in NK-cell depleted adherent cells after prolonged 18 hr incubation. The cell population responsible for this dichotomous effect of PMA on adherent cell-mediated cytotoxicity was shown to be monocytes, as revealed by monoclonal antibody treatment. Pure NK cell preparations were not affected by PMA in their cytolytic capacities. Reactive oxygen species are not involved in NK-cell mediated cytotoxicity, while PMA stimulated the monocytes to exert cytolysis and suppressed NK cells by the generation of these highly toxic oxygen products. Hydrogen peroxide especially seemed to be the mediator in this oxygen-dependent monocyte-mediated cytotoxicity and NK-cell suppression.     

Relapses after stopping chemotherapy for experimental tuberculosis in genetically resistant and susceptible strains of mice.

Three strains of mice (Swiss albinos, C57BL/6,C3H/OuJ) were injected intravenously with 3.7 x 10(6) colony forming units (CFU) of M. tuberculosis, H37RV, sensitive and resistant to antibiotics (90% of bacilli sensitive, 9% resistant to Streptomycin and 0.9% resistant to Kanamycin). Two weeks later, chemotherapy was started 6 days a week for a 6-month period with isoniazid (INH) and rifampicin (RMP). Twenty mice of each strain were killed at the end of the chemotherapy and the others were kept without antibiotics for a second 6-month follow-up period before being killed. The early multiplication of bacilli during the first 2 weeks following infection and before chemotherapy, was similar in the three strains of mice. Chemotherapy had the same apparent efficacy in the three strains of mice, nearly all the mice being cured as assessed by a negative spleen culture on Loewenstein-Jensen medium at the end of chemotherapy. But after the 6-month follow-up period, the C3H strain presented a statistically significantly higher level of positive spleen culture ('relapse') than seen in the C57BL/6 strain, and an increased number of mycobacteria per relapsing mouse spleen. It has been estimated with the help of resistant and sensitive bacilli that the relapses were due in most of the cases to the regrowth of one or very few bacilli, giving a clone. It seems that the C3H strain of mice, known to carry the Bcg-r allele of the Bcg gene, might be less able to develop a specific acquired resistance capable of stopping the delayed development of a highly virulent strain of mycobacteria.     

Recombinant human interleukin 1 alpha enhances anti-Listeria resistance in both genetically resistant and susceptible strains of mice

In this study we show that recombinant human IL-1 alpha (rhIL-1 alpha) protects both genetically resistant and susceptible strains of mice against Listeria monocytogenes infection. Similar levels of protection were observed in all strains tested. These data suggest that innate susceptibility to an infectious agent may not abrogate the ability of rhIL-1 alpha to enhance antibacterial resistance.     

Macrophage activation during Plasmodium chabaudi AS infection in resistant C57BL/6 and susceptible A/J mice.

Macrophage activation was examined in resistant C57BL/6 and susceptible A/J mice during the course of blood-stage infection with Plasmodium chabaudi AS. Three parameters of macrophage activation (lipopolysaccharide [LPS]- and malaria antigen-induced tumor necrosis factor [TNF] production in vitro, phorbol myristate acetate [PMA]-induced production of oxygen metabolites in vitro, and Ia antigen expression) were assessed during infection in populations of peritoneal and splenic macrophages recovered from infected mice of the two strains. The peak level of LPS-induced TNF production in vitro by splenic macrophages from both infected C57BL/6 and infected A/J mice occurred on day 7, which was 3 days before the peak of parasitemia. Although the kinetics of TNF production in vitro in response to either LPS, soluble malaria antigen, or intact parasitized erythrocytes varied in some of the other macrophage populations during infection, there was no significant difference in the peak level of production. Peritoneal and splenic macrophages from infected C57BL/6 mice exhibited significantly increased PMA-induced production of H2O2 in vitro on day 7. Peritoneal macrophages from infected A/J mice also exhibited significant PMA-induced H2O2 production on day 7, while production by splenic macrophages from these hosts was not increased in comparison with production by cells from normal animals. Only peritoneal macrophages from infected C57BL/6 mice produced significantly increased levels of O2-, and this occurred on day 7 postinfection. Ia antigen expression by both peritoneal and splenic macrophages from resistant C57BL/6 and susceptible A/J mice was significantly increased during P. chabaudi AS infection. However, the percentage of Ia+ peritoneal macrophages on days 8 and 10 postinfection and Ia+ splenic macrophages on day 3 postinfection was significantly higher in C57BL/6 than in A/J mice. Thus, these results demonstrate that macrophages from P. chabaudi AS-infected A/J mice exhibit defects in oxygen metabolism and Ia antigen expression which may contribute to the susceptibility of these hosts to this intraerythrocytic parasite. The cause-and-effect relationship between these defects and the susceptibility of A/J mice to P. chabaudi AS is unknown.     

Resistance to listeriosis in two lines of mice genetically selected for high and low antibody production.

Infection by the intracellular parasite Listeria monocytogenes was studied in two inbred lines of mice genetically selected for high and low antibody production against xenogeneic red blood cells. It was revealed that, during the early non-specific phase of infection, bacterial growth in tissues was significantly enhanced in high responder (HR) mice, as opposed to low responder (LR) mice. This is interpreted as the in vivo expression of a genetic impairment of the bactericidal activity of resident macrophages in this line of mice. After Day 2 of infection, the kinetics of bacterial growth in the spleen and the liver was almost identical in the two lines, indicating that mice from both lines generated efficient anti-Listeria immunity. This was confirmed by the fact that no interline difference could be detected in the expression of T-cell mediated immunity, as estimated by the production of protective T cells and delayed sensitivity T cells, and by the level of immunological memory. The genetic impairment in the bactericidal activity of resident macrophages resulted in a significant increase of anti-Listeria antibody production in HR mice and did not prevent T-dependent activation of effector macrophages mobilized in infectious sites. This explains that the overall resistance to listeriosis was similar in LR and HR mice, as shown by the LD50 values respectively estimated as 2.2 X 10(5) and 3.8 X 10(5) bacteria per mouse. This natural resistance was expressed at the same level as that of C57BL/6 mice.     

Macrophage colony-stimulating factor gene expression in vascular cells and in experimental and human atherosclerosis.

The infiltration of monocytes into the vascular wall and their transformation into lipid-laden foam cells characterizes early atherogenesis. Macrophages are also present in more advanced human atherosclerotic plaques and can produce many mediators that may contribute to lesion formation and progression. Macrophage colony-stimulating factor (MCSF) enhances the proliferation and differentiation of monocyte progenitors and is required for the survival and activation of mature monocytes and macrophages. The authors therefore examined the expression of the MCSF gene in cultured human vascular endothelial (EC) and smooth muscle cells (SMC) as well as in atheromatous lesions from rabbits and humans. Growth arrested EC and SMC contain a low level of MCSF mRNA. Bacterial lipopolysaccharide (LPS), recombinant human interleukin-1 alpha (IL-1 alpha) or tumor necrosis factor alpha (TNF alpha) induced MCSF mRNA accumulation in a concentration-dependent manner in both EC and SMC. These stimuli induced large increases in MCSF mRNA with peak induction between 4-8 hours after treatment. LPS, IL-1 alpha, and TNF alpha stimulated EC and SMC also showed increased fluorescent antibody staining for MCSF protein and released immunoreactive MCSF in a time-dependent manner. In contrast, phorbol 12-myristate 13-acetate (PMA) was a less potent inducer of MCSF gene expression and iron-oxidized low-density lipoproteins (ox-LDL) did not increase consistently MCSF mRNA or the synthesis and secretion of immunoreactive protein. Northern analysis of mRNA isolated from the atheromatous aorta of rabbits fed a 1% cholesterol diet for 10 weeks showed elevated MCSF mRNA compared with controls. Immunostaining of atheromatous arterial lesions of rabbits demonstrated MCSF protein in association with intimal SMC as well as macrophages. Furthermore, polymerase chain reaction (PCR) analysis of MCSF mRNA in human atheromata showed higher levels than found in nonatherosclerotic arteries and veins. Since the authors found no mRNA for the MCSF receptor, c-fms, in cultured EC or SMC macrophages are likely the primary target for MCSF within atheromatous vessels. The authors therefore investigated the effects of MCSF on monocyte functions related to foam cell development. Treatment of cultured human monocytes with recombinant human MCSF (10(3) U/ml, 72 hr) led to the accumulation of mRNA for the acetyl-LDL (scavenger) receptor and apolipoprotein E (apo E). These studies establish that vascular EC and SMC produce substantial MCSF in response to a variety of stimuli. The local production of MCSF during atherogenesis may contribute to macrophage survival and proliferation or activate specific macrophage functions such as expression of the scavenger receptor and secretion of apo E.