Role of macrophages in resistance of mice to experimental cryptococcosis.

Mice with either a stimulated or depressed reticuloendothelial system were used to study the role of macrophages in resistance to experimental Cryptococcus neoformans infection. Silica, administered intravenously to destroy macrophages, considerably decreased the phagocytic index of the reticuloendothelial system as determined by a carbon clearance test. Silica given 1 day before intravenous challenge with 5 X 10(3) (1 50% lethal dose) of C. neoformans markedly decreased the resistance of mice to cryptococcal infection. Mice given repeated doses of BCG to nonspecifically activate their macrophages could withstand a challenge of 100 50% lethal doses of C. neoformans. These results provide evidence that macrophages play an essential role in natural or nonspecific cell-mediated immunity to murine cryptococcosis.     

Role of activated macrophages in resistance to systemic candidosis

To evaluate further the contribution of activated macrophages in resistance, the course of systemic candidosis was assayed in beige and NLM mice that had been previously infected with Mycobacterium bovis (BCG). Four weeks following BCG infection, mice were inoculated intravenously with 1 x 10(4) viable Candida albicans. At various times thereafter, the number of C. albicans colony-forming units in the livers, spleens, and kidneys was determined. The average number of CFU recovered from the kidneys of NLM mice decreased throughout the assay and was comparable in both BCG-treated and control mice. In contrast, the number of CFU cultured from the kidneys of untreated control beige mice progressively increased throughout the assay period. This profile of renal susceptibility was not appreciably altered in BCG-treated beige mice. However, fewer (10- to 100-fold) CFU were cultured from the livers and spleens of BCG-treated beige and NLM mice than from untreated controls. These results support the hypothesis that in the absence of functional polymorphonuclear leukocytes, activated macrophages represent a means to control the proliferation of C. albicans.     

Role of macrophages in host resistance to group A streptococci

Macrophages provide the first line of defense against invading pathogens. The aim of this study was to determine the role of macrophages during infection with group A streptococci (Streptococcus pyogenes) in mice. Here, we report that resident macrophages can efficiently take up and kill S. pyogenes during in vivo infection, as demonstrated by immunofluorescence and electron microscopy, as well as colony counts. To evaluate the contribution of macrophages to the resolution of experimental infection with S. pyogenes, we compared the susceptibility of BALB/c mice rendered macrophage deficient by treatment with carrageenan with that of intact mice. The results show that depletion of macrophages enhanced the susceptibility of BALB/c mice to S. pyogenes infection, as evidenced by 100% mortality of macrophage-depleted mice compared to 90% survival of nondepleted control animals. The in vivo depletion of macrophages strongly enhanced bacterial loads in the blood and systemic organs. Resistance to S. pyogenes can be restored in macrophage-depleted mice by adoptive transfer of purified macrophages. The in vivo blocking of the macrophage phagocytic function by treatment with gadolinium III chloride also resulted in enhanced susceptibility to S. pyogenes. Interestingly, depletion of macrophages prior to or during the first 24 h of infection decreased survival dramatically; in contrast, no mortality was observed in infected nondepleted animals or mice depleted after 48 h of infection. These results emphasize the important contribution of macrophages to the early control of S. pyogenes infection.     

Role of macrophages in innate and acquired host resistance to experimental scrub typhus infection of inbred mice.

Mechanisms of innate resistance to infection with the Gilliam strain of Rickettsia tsutsugamushi were examined using congenic strains of mice resistant (C3H/RV) or susceptible (C3H/He) to intraperitoneal infection. Both strains of mice were resistant to infection with 1,000 50% mouse lethal doses of rickettsiae if given intravenously. In both systems rickettsial replication occurred after intravenous infection, as evidenced by an increase in rickettsial numbers in the spleens of infected animals, followed by a decrease in rickettsiae to low levels by day 14 postinfection. Administration of the antimacrophage agents silica and carrageenan to C3H/He mice intravenously rendered these animals susceptible to lethal infection. Neither irradiation nor silica given individually rendered C3H/RV mice susceptible to intravenous infection. However, if silica and irradiation were given together, a lethal infection occurred after intravenous infection. C3H/RV mice became susceptible to lethal infection after sublethal doses of irradiation only if they were infected intraperitoneally. Administration of silica or carrageenan had no effect on the outcome of intraperitoneal infection of these mice with Gilliam rickettsiae. These data suggest that both strains of mice share innate resistance mechanisms to intravenous infection that consist of fixed macrophages. Resistance of C3H/RV mice to intraperitoneal infection, in contrast, apparently was dependent only on an irradiation-sensitive process.     

A role for sialoadhesin-positive tissue macrophages in host resistance to lymphoma metastasis in vivo.

Sialoadhesin (SER) is a newly described macrophage-restricted adhesion molecule with a sequence similarity to CD22 on B cells and to myelin-associated glycoprotein on Schwann cells. We describe here a functional role of SER+ spleen macrophages in antigen processing and presentation to T lymphocytes. In two syngeneic murine tumour systems (ESb-MP and lacZ transduced ESbL T-lymphoma cells), the activation state of SER+ macrophages (tested by activity of marker enzymes adenosine deaminase and 5'-nucleotidase) correlated with the arrest of lymphoma metastasis. Furthermore, this macrophage subpopulation became activated upon anti-tumour immunization as well as upon adoptive transfer of immune T lymphocytes into tumour-bearing hosts. We suggest that in situ-activated SER+ macrophages contribute to host resistance against metastasis.     

Ultrastructure of pulmonary alveoli and macrophages in experimental Legionnaires' disease

Guinea pigs, rhesus monkeys and marmosets infected with Legionella pneumophila in small particle aerosols developed an acute fibrinopurulent bronchopneumonia. Changes from 24 hr included exudation into alveoli of protein-rich, often fibrinous fluid and many polymorphonuclear leucocytes (PMN) and macrophages. Damage to alveolar capillary endothelium consisted of widespread cytoplasmic swelling and vesiculation, but necrosis of endothelium and the associated alveolar epithelium was focal and less common. Phagocytosis of L. pneumophila organisms was predominantly by macrophages, but the bacteria were also seen in PMN. Free organisms were present in alveoli and capillary lumina at all stages of the infection but were not observed in lung parenchymal cells. Some infected macrophages and PMN became necrotic and lysed to release intact bacteria. In all species of experimental animal, intracytoplasmic aggregations of granular material, believed to be glycogen, were seen frequently in macrophages and PMN which had phagocytosed L. pneumophila. These deposits of glycogen may reflect either an increased energy demand by the host cell or an interference with its carbohydrate metabolism.     

Role of Calomys musculinus peritoneal macrophages in age-related resistance to Junin virus infection

In nature, the cricetid Calomys musculinus is the principal host of Junin virus, the etiological agent of Argentine hemorrhagic fever. In the experimental infection, adult C. musculinus survived whereas newborns died after intraperitoneal inoculation with the XJ.Cl3 strain of Junin virus. The role of peritoneal macrophages in this age-related resistance was studied. Junin virus multiplied in cultivated macrophages from either neonatal or adult animals and, therefore, it was not possible to correlate the susceptibility of peritoneal macrophages to Junin virus infection with the age-dependent resistance. When adult and neonatal animals were treated with silica prior to Junin virus infection, deaths occurred in the adults, while a delay and decrease in the mortality rate were observed in neonatals. These results suggest that in neonatal C. musculinus macrophages could be permissive cells for Junin virus multiplication, whereas in adult cricetids, these cells would act as a barrier against viral infection by means of an extrinsic antiviral activity.     

Role of murine macrophages and complement in experimental Campylobacter infection

The roles of macrophages and the complement system as potential host defence mechanisms in mice against campylobacter infection were studied in vivo, by depleting the murine serum-complement or the phagocytic cells. Macrophage-depletion was performed by intraperitoneal (i.p.) injection of silica dust, Liquoid or dextran sulphate. During 5 days after infection, such mice showed a significant increase in mortality, compared with controls. In contrast, mice that were previously decomplemented by i.p. injection of Cobra Venom Factor showed no significant increase in mortality. The results with combined macrophage depletion and decomplementation did not differ from those with macrophage depletion alone. These experiments suggest that macrophages seem to be more important than complement in the defence of mice against experimental campylobacter infection.     

Role of leukocyte breakdown products in increasing the resistance of macrophages to ornithosis virus

The dynamics of formation of macrophagal granulomas in the liver after intravenous infection of albino mice with ornithosis virus was studied. During granuloma formation the macrophages pass through a stage of reutilization of breakdown products of leukocytes and they become resistant to ornithosis virus. Together with remnants of leukocytes, histones and cationic proteins with high antiornithosis activity in vitro may also enter the cytoplasm of the macrophages. The increased resistance of macrophages to the virus after reutilization of the leukocyte breakdown products is evidently one of the mechanisms of resistance formation in inflammatory foci associated with ornithosis.Laboratory of Pyrogens and Nonspecific Resistance, Department of General Pathology, Institute of Experimental Medicine, Academy of Medical Sciences of the USSR. Laboratory of Protein Chemistry, A. A. Zhdanov University, Leningrad. (Presented by Academician of the Academy of Medical Sciences of the USSR P. N. Veselkin.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 5, pp. 584–587, May, 1976.     

Role of macrophages in the pathogenesis of experimental tick-borne encephalitis in mice

In vivo phagocytosis activity of macrophages (PAM) was temporarily suppressed in mice by application of a suspension of microscopic from particles. As demonstrated, a reversible block of 70% of PAM was accompanied by a marked increase of the lethality during the acute tick-borne encephalitis (TBE) virus infection. Asymptomatic persistence of TBE virus in the brain was 4 times more frequent in mice with PAM defect than in immuno-competent mice. Suppression of PAM during the first 48 hr post infection (p.i.) did not affect interaction of B-, T-lymphocytes and macrophages. Cytotoxic activity of splenocytes against TBE virus-infected mouse embryo fibroblasts (MEF) was alike irrespective of whether cytotoxic cells were collected from mice inoculated or not inoculated with microscopic iron suspension. Similarly, frequency of seroconversion did not differ in these groups of mice. Adoptively transferred peritoneal macrophages from TBE virus-infected or intact mice did not exert any protective activity. The presence of splenic macrophages was necessary neither in adoptive immunity transfer in vivo nor in cytotoxic activity of T-lymphocytes directed to virus-infected targets in vitro. It was further found that peritoneal macrophages (PM) both from TBE virus immunized and non immunized donors in the presence of antibodies to TBE virus acquired the capability to kill TBE virus-infected target cells. Antibody-dependent cytotoxicity (ADC) of macrophages was associated with population of phagocytic cels.(ABSTRACT TRUNCATED AT 250 WORDS)     

The stereology of pulmonary alveolar macrophages after prolonged experimental exposure to tobacco smoke.

Morphometric analysis was performed on alveolar macrophages obtained by bronchopulmonary lavage of rats exposed to tobacco smoke for periods up to 60 consecutive days. Smoke dosage levels were adjusted so as to be comparable to those of human smokers. Size distributions were obtained for the lavaged macrophage populations of treated and age-matched control animals following 30 and 60 days of smoke exposure. Electron microscopic stereology was used to quantitate alterations in the ultrastructure of the same macrophage preparations. Several significant changes were observed in macrophage morphology following exposure to tobacco smoke, with an estimated mean cell volume more than twice that of controls following 60 days of smoking. After 30 and 60 days of exposure there was a 10- and 16-fold increase, respectively, in the volume density of cytoplasmic lipid inclusions. The surface to volume ratio of the cells and the lysosomal volume density were reduced in macrophages from smoke-exposed animals. A possible relationship between the incidence of lysosomes and the accumulation of cytoplasmic lipid in treated cells is discussed.     

Role of macrophages/microglia in multiple sclerosis and experimental allergic encephalomyelitis

 One of the characteristic features of microglia is their rapid activation in response to injury, inflammation, neurodegeneration, infection, and brain tumors. This review focuses on the role of the microglia in multiple sclerosis (MS), a chronic inflammatory demyelinating disease of the central nervous system (CNS), and in the animal model of MS, experimental allergic encephalomyelitis (EAE). Microglial activation in MS and EAE is thought to contribute directly to CNS damage through several mechanisms, including production of proinflammatory cytokines, matrix metalloproteinases, and free radicals. In addition, activated microglia serve as the major antigen-presenting cell in the CNS, likely contributing to aberrant immune reactivity at this site. A mechanistic understanding of the way in which microglia are activated and ultimately inhibited is crucial for the formulation of therapeutic modalities to treat MS and other CNS autoimmune diseases. Received: 6 June 1996 / Accepted: 4 October 1996     

Role of pulmonary alveolar macrophages in defense of the lung against Pseudomonas aeruginosa

Alveolar macrophages (AM) provide one of the first lines of defense against microbial invasion in the lower airways. The role of AM in the clearance of Pseudomonas aeruginosa in mice after intrapulmonary challenge was evaluated. AM were depleted by intranasal administration of liposome-encapsulated dichloromethylene diphosphonate. At 24 h following the instillation of liposomes, a sublethal dose of P. aeruginosa was inoculated intranasally. Spleen, liver, and lung tissue was then evaluated for viable bacteria and for histopathology. AM depletion of 78 to 88% did not affect the survival rate of infected mice or clearance of P. aeruginosa from the spleen, liver, or lung, compared to the control group, but the mice's susceptibility to Klebsiella pneumoniae was greatly enhanced. The recruitment of neutrophils to the lung was also not affected. Freshly explanted AM were not competent to phagocytose unopsonized P. aeruginosa but were able to phagocytose zymosan particles. Further studies were conducted to assess the in situ phagocytic activities of AM. Three hours after the intranasal instillation of P. aeruginosa or other particles, bronchoalveolar lavage was performed. AM phagocytosis of zymosan particles and latex beads exceeded that of P. aeruginosa. Neutrophils were recruited to the lung in response to a high-dose bacterial challenge. These results suggest that AM do not play an important role in defense of the lung against P. aeruginosa.     

Response of pulmonary macrophages to lead.

The intratracheal instillation of moderate doses of PbO to Long-Evans strain rats resulted in a significant increase in the number of recoverable pulmonary alveolar macrophages. The viability of recovered cells was remarkably constant throughout the experimental period of 40 days. The results obtained indicate a low order of toxicity of PbO to alveolar macrophages and show that the mucociliary escalator is a significant route of excretion of PbO from the respiratory tract. The in vitro survival of macrophages from PbO-treated rats was significantly reduced. Survival of cells from both treated and control animals was somewhat enhanced by the addition of formalinized lymphocytes to the culture medium. Morphological changes and evidence of phagocytosis are discussed.     

Role of macrophage activation and interferon in the resistance of alveolar macrophages from infected mice to influenza virus

Lung macrophages from uninfected CD1 mice support the replication of influenza viruses (H1N1 and H0N1), but the cells from influenza-infected mice do not. The possible mechanisms of this resistance were investigated. Murine macrophages were "activated" in vitro with lipopolysaccharide and lymphokines, and in both cases activation was associated with resistance of cells to infection with influenza virus. Exposure of alveolar macrophages in vitro to 500 U of purified type I interferon per ml enhanced cell spreading and Fc receptor-mediated phagocytosis, suggesting macrophage activation, and protected the cells against infection with influenza virus. Alveolar macrophages were also protected by a soluble factor in the bronchoalveolar washings from influenza-infected mice. This effect was not virus specific and was abolished by anti-interferon serum.     

Functional resistance of inflammatory macrophages to methotrexate in vitro

The purpose of this study was to evaluate the effects of high and low therapeutic doses of methotrexate (MTX) on macrophage metabolism and function in vitro. Monolayers of elicited rat peritoneal macrophages (PM) were exposed to a wide range of MTX concentrations (10(-8) M-10(-3) M) for 24 or 48 hr and macrophage RNA and protein metabolism were evaluated by the incorporation of [3H]5-uridine and [14C]1-leucine, respectively, into trichloroacetic acid (TCA)-precipitable material. Macrophage functional activity was examined by measuring the uptake of [14C]Pseudomonas aeruginosa to assess phagocytosis and the release of 51Cr from antibody-coated [51Cr]sheep red blood cells (SRBC) to assess antibody-dependent cell-mediated cytotoxicity. Following a 24-hr incubation with 10(-3) M MTX, incorporation of [3H]5-uridine into PM monolayers was enhanced 79% when compared to control monolayers (p less than 0.005). Washout studies revealed that the stimulation of uridine incorporation was no longer observed by 24 hr following the removal of MTX from the culture medium. Incubation with 10(-3) M MTX for 48 hr returned uridine incorporation to control levels, although leucine incorporation into protein was reduced by 22% (p less than 0.01). The depression in leucine incorporation in the presence of 10(-3) M MTX was not reversed after the removal of MTX from the culture medium. Uptake of [14C]P. aeruginosa was not altered following a 24- or 48-hr incubation with either 10(-7) M or 10(-3) M MTX. Similarly, [51Cr]SRBC cytolysis was not affected by a 2-hr preincubation with and continuous exposure to between 10(-8) M and 10(-3) M MTX. These results demonstrate that incubation of inflammatory macrophages with clinically high doses of MTX can alter macrophage RNA and protein metabolism without producing demonstrable changes in macrophage functional activity.     

Response of pulmonary macrophages to unilateral instillation of carbon

Production and delivery of macrophages to the alveoli are dependent upon chemotactic and mitogenic stimuli. To determine whether these mechanisms occur uniformly throughout the lungs or are localized to the areas of particulate deposition, the authors instilled 4 mg of carbon in one lung of a rat, the other lung serving as a control. Following split-lung lavage, little change was seen in the number of cells lavaged from nontreated lungs, whereas the yield of macrophages from the black lungs rose from 32 X 10(4) to 400 X 10(4) after 2 days; control values were not attained until 3 weeks. Labeling indices for cell nuclei in the white lungs were slightly elevated, whereas in the black lungs the value rose from 0.4 to 1.0-1.5% for 3 weeks before falling to normal. The increased labeling was limited to interstitial cells. The results provide further support for the dual origin of alveolar macrophages and indicate the importance of local generation of chemotactic and mitogenic factors in stimulating the cellular response and in directing these cells to the sites of maximal deposition of particles.