Chemotactic and candidacidal responses of rabbit alveolar macrophages during postnatal development and the modulating roles of surfactant in these responses

Pediatric Tuberculosis Management: A Global Challenge or Breakthrough?

Managing pediatric tuberculosis (TB) remains a public health problem requiring urgent and long-lasting solutions as TB is one of the top ten causes of ill health and death in children as well as adolescents universally. Minors are particularly susceptible to this severe illness that can be fatal post-infection or even serve as reservoirs for future disease outbreaks. However, pediatric TB is the least prioritized in most health programs and optimal infection/disease control has been quite neglected for this specialized patient category, as most scientific and clinical research efforts focus on developing novel management strategies for adults. Moreover, the ongoing coronavirus pandemic has meaningfully hindered the gains and progress achieved with TB prophylaxis, therapy, diagnosis, and global eradication goals for all affected persons of varying age bands. Thus, the opening of novel research activities and opportunities that can provide more insight and create new knowledge specifically geared towards managing TB disease in this specialized group will significantly improve their well-being and longevity.

Immunomodulatory properties of surfactant preparations

Surfactant replacement significantly decreased acute pulmonary morbidity and mortality among preterm neonates with respiratory distress syndrome. Besides improving lung function and oxygenation, surfactant is also a key modulator of pulmonary innate and acquired immunity regulating lung inflammatory processes. In this review, we describe the immunomodulatory features of surfactant preparations. Various surfactant preparations decrease the proinflammatory cytokine and chemokine release, the oxidative burst activity, and the nitric oxide production in lung inflammatory cells such as alveolar neutrophils, monocytes and macrophages; they also affect lymphocyte proliferative response and immunoglobulin production, as well as natural killer and lymphokine-activated killer cell activity. In addition, surfactant preparations are involved in airway remodeling, as they decrease lung fibroblast proliferation capacity and the release of mediators involved in remodeling. Moreover, they increase cell transepithelial resistance and VEGF synthesis in lung epithelial cells. A number of different signaling pathways and molecules are involved in these processes. Because the inhibition of local immune response may decrease lung injury, surfactant therapeutic efficacy may be related not only to its biophysical characteristics but, at least in part, to its anti-inflammatory features and its effects on remodeling processes. However, further studies are required to identify which surfactant preparation ensures the highest anti-inflammatory activity, thereby potentially decreasing the inflammatory process underlying respiratory distress syndrome. In perspective, detailed characterization of these anti-inflammatory effects could help to improve the next generation of surfactant preparations.

Surfactant protein A binds TGF-β1 with high affinity and stimulates the TGF-β pathway

We were able to demonstrate reversible, specific and high-affinity binding of radioactively-labelled TGF-β1 (125I-TGF-β1) to immobilized surfactant protein A (SP-A), with an apparent dissociation constant of 53 picomolar at ∼21℃. Addition of a 200-fold molar excess of the latency associated peptide (LAP) prevented and dissociated the binding of 125I-TGF-β1 to SP-A, whereas latent TGF-β1 had no effect. Using a bioassay for TGF-β1 activity—a luciferase reporter assay—we were able to show that SP-A in the presence of TGF-β1 stimulated the TGF-β1 pathway, whereas SP-A alone had no effect. Studies with structural analogues of the distinct SP-A tail domain and head domain indicated that stimulatory activity of SP-A resided in the head domain. No activation of latent TGF-β1 by SP-A was observed. In addition, we observed that SP-A inhibited TGF-β1 inactivation by LAP. These results indicate that SP-A may have a regulatory role in the TGF-β1-mediated processes in the lung.

Perinatal tuberculosis: new challenges in the diagnosis and treatment of tuberculosis in infants and the newborn

With increasing rates of tuberculosis (TB) infection and disease worldwide, the rate of perinatal TB is also affected. A high index of suspicion by health professionals, in both the developed and developing world, is required to detect and manage tuberculosis in pregnancy and the early newborn period. Differences in immune responses in the fetus and neonate add to the diagnostic difficulties already recognised in young children. Although specific guidelines for the treatment of this potentially devastating disease are lacking due to paucity of experience, outcome is favourable, if the condition is recognised and treated according to existing TB protocols. HIV co-infection, multi- and extensively-drug resistant (MDR/XDR) TB contribute to the challenges. New diagnostic and vaccine developments hold future promise, but much work is needed to completely understand the complex immune responses to tuberculosis and control this disease.

Paediatric tuberculosis

Tuberculosis continues to cause an unacceptably high toll of disease and death among children worldwide, particularly in the wake of the HIV epidemic. Increased international travel and immigration have led to a rise in childhood tuberculosis rates even in traditionally low burden, industrialised settings, and threaten to promote the emergence and spread of multidrug-resistant strains. Whereas intense scientific and clinical research efforts into novel diagnostic, therapeutic, and preventive interventions have focused on tuberculosis in adults, childhood tuberculosis has been relatively neglected. However, children are particularly vulnerable to severe disease and death following infection, and those with latent infection become the reservoir for future transmission following disease reactivation in adulthood, fuelling future epidemics. Further research into the epidemiology, immune mechanisms, diagnosis, treatment, and prevention of childhood tuberculosis is urgently needed. Advances in our understanding of tuberculosis in children would provide insights and opportunities to enhance efforts to control this disease.

Effects of surfactant lipids and surfactant protein a on host defense functions of rat alveolar macrophages

Survanta is commonly used as replacement therapy in newborn infants suffering from surfactant deficiency. We investigated the effects of Survanta and surfactant-like liposomes in the presence and absence of surfactant protein A (SP-A) on host defense functions of rat alveolar macrophages (AM). Phagocytosis of Streptococcus pneumoniae by AM was significantly inhibited in the presence of 100 microg/mL of Survanta. The ability of SP-A to enhance phagocytosis of S. pneumoniae was significantly compromised upon exposure to either Survanta or liposomes, although the overall level of phagocytosis remained higher than in the absence of SP-A. This inhibitory effect was not overcome by opsonization of the bacteria with SP-A before incubation with Survanta and AM. We also found that the ability of SP-A to mediate the association of group B Streptococcus with AM was compromised to a significant degree when exposed to either Survanta or liposomes in concentrations of 150 and 250 microg/mL. However, at most concentrations of Survanta or liposomes tested, the presence of SP-A resulted in significantly higher levels of bacterial association. These data show that Survanta and surfactant-like lipids suppress host defense functions of AM in the presence and absence of SP-A in vitro, although SP-A continues to enhance host defense functions overall.

In vitro effect of lung surfactant on alveolar macrophage defence mechanisms against Cryptococcus neoformans

The effects of a modified natural porcine surfactant (Curosurf) on phagocytosis and killing of Cryptococcus neoformans by alveolar macrophages and on the production of superoxide anions were investigated in vitro. Attachment and ingestion were evaluated separately by a fluorescent quenching technique. The nitroblue tetrazolium reduction test was used as an indirect measurement of superoxide anion production. Killing was assessed by a colony-forming assay. Surfactant induced increased ingestion of C. neoformans, unopsonized as well as opsonized with fresh serum or anticryptococcal polyclonal IgG. Surfactant had, however, no effect on the attachment or killing of unopsonized or opsonized C. neoformans by the alveolar macrophages. In addition, the enhancement of the oxidative metabolism of the macrophages after stimulation with opsonized yeast was impaired, although the killing was not affected. This study indicates that in vitro Curosurf can influence the alveolar macrophage defence against C. neoformans by enhancing its ingestion and by interacting with the superoxide anions release from alveolar macrophages stimulated with fresh serum or anticryptococcal polyclonal IgG opsonized yeast cells.

Neutrophil sequestration in the lung following acute aortic occlusion starts during ischaemia and can be attenuated by tumour necrosis factor and nitric oxide blockade

OBJECTIVES

To investigate the role of lower extremity ischaemia in acute lung injury with special emphasis on the role of tumour necrosis factor (TNF) and nitric oxide (NO) as mediators of neutrophil (PMN) chemotaxis in the lung.

DESIGN

Prospective randomised study.

MATERIALS AND METHODS

Sprague-Dawley rats were randomized into four groups: group 1 (x-clmap): aorta clamped just above the bifurcation for 3 h; group 2 (AG): 50 mg/kg aminoguanidine, a specific inducible NO synthase (iNOS) inhibitor, was administered prior to aortic occlusion; group 3 (Steroids): 1 mg/kg dexamethasone was administered prior to aortic occlusion; and group 4 (TNFbp): 2 mg/kg TNFbp, a PEGylated dimeric form of the high affinity TNF receptor I (R1) was administered prior to aortic occlusion to block TNF action. Groups 2, 3 and 4 were subjected to the same ischaemia time as group 1. NO concentration in the exhaled gas (ENO) was measured in 30 min intervals. At the end of the 3 h ischaemia, one lung was excised and fixed for routine histological evaluation, and the other underwent bronchoalveolar lavage (BAL). PMN chemotaxis towards the BAL fluid was then measured using the blindwell technique.

RESULTS

ENO in group 1 increased from 0.9 +/- 0.3 ppb at baseline, to 41.3 +/- 9.2 ppb at the end of ischaemia. Animals in this group exhibited significant lung inflammation. Aminoguanidine, dexamethasone and TNFbp blocked NO production (peak ENO values of 7.2 +/- 1.9, 12.6 +/- 1.3 and 8.9 +/- 1.7 ppb for groups 2, 3 and 4 respectively), decreased PMN chemotaxis and sequestration in the lung, and attenuated lung inflammation.

CONCLUSIONS

Acute lung injury resulting from distal aortic occlusion starts during ischaemia. TNF and NO blockade decrease PMN chemotaxis and sequestration and attenuate the lung injury process.

Effects of pulmonary surfactant on macrophage migration: suppression of chemokinesis by surfactant phospholipid and enhancement of chemotaxis by surfactant protein

We fractionated the bronchoalveolar lavage fluid (BALF) from normal rabbit lungs into several fractions by high speed centrifugation and ethanol-ether extraction. Random migration, chemokinesis and chemotaxis of freshly harvested alveolar macrophages (AM), 24 h cultured AM, and peritoneal exudate cells (PEC) were assayed in vitro using a modified, under agarose method and a blind well chemotactic chamber method. Freshly harvested AM demonstrated little random migration compared with PEC. However, when freshly harvested AM were pre-incubated in surfactant free medium for 24 h, the cells showed the same rate of migration as PEC. The increased migration of the 24 h cultured AM was partially suppressed by the presence of all BALF fractions containing high proportions of phospholipid. The inhibition by Fr-L (a fraction enriched in phospholipids) was reversed by normal serum, but not by heat-inactivated serum, cholesterol, synthetic dipalmitoyl phosphatidyl choline, or indomethacin. Fr-L markedly suppressed macrophage chemokinesis but did not affect on macrophage chemotaxis. Alternatively, Fr-P, a delipidated preparation of surfactant consisting mainly of protein, had no effect on macrophage chemokinesis but increased the chemotaxis of PEC to zymosan-activated serum. We conclude that surfactant phospholipid suppresses AM migration, while surfactant protein increases macrophage chemotaxis.

Amplified nitric oxide production by pulmonary alveolar macrophages of newborn rats

Oxygen (O2)-dependent and O2-independent antimicrobial mechanisms are used by alveolar macrophages (AM) to maintain lung sterility, but these mechanisms are underdeveloped in neonatal AM. Nitric oxide (NO(.)), a more recently described antimicrobial and immunomodulating molecule, has not been studied in neonatal AM. Lavaged AM from 3-day-old, 10-day-old, maternal and adult rats were treated with or without lipopolysaccharide (LPS) and/or interferon-γ (IFN-γ) and NO(.) synthase activity was measured as its L-arginine metabolites: NO2(-), NO3(-), and citrulline. Superoxide anion (O2(.-)) production by suspended macrophages, initiated by either opsonized zymosan or phorbol, was used as a marker of O2-dependent antimicrobial activity. Lysozyme content of AM was measured as a component of O2-independent antimicrobial activity. Unstimulated 3-day-old macrophages generated >10-fold more NO2(-) + NO3(-) than did 10-day-old, maternal or adult AM. Twenty hours after LPS and IFN-γ stimulation, 3-day-old AM produced > 2 times more NO2(-) and NO3(-) than did the more mature macrophages. Basal and stimulated O2(.-) release was similar among 3-day-old, 10-day-old and adult AM, while lysozyme concentrations were > 4-fold higher in adult macrophages compared to AM from 3-day-old pups. Rather than having a role in NO(.)-dependent antimicrobial activity, we propose that newborn AM have amplified NO(.) production to modulate their own differentiation and replication after birth. The age-dependent differences in NO(.) synthase expression by AM may lend insight into the regulation of this important enzyme.

Developmental aspects of pulmonary defenses in children

It is now generally accepted that maturational immaturity of lung defense system(s) exists in the young infant and child which, together with other maturational deficiencies of immunologic systems, contribute to their undue susceptibility to infections, many of which are associated with pulmonary infections. The alveolar macrophage (AM), of central importance to lung defense, has been studied extensively in the neonatal rabbit by our group and in the human, by others. Collectively, the results indicate small numbers of morphologically and functionally immature AMs prior to birth followed by a dramatic increase within the first 24 hr. This increase coincides with the large release from type II cells of surfactant, which not only may be involved in the functional maturation of developing AMs but also, if present in large quantities, may lead to decreased activity of these cells. There is also an age-related increase in chemotactic and microbicidal activity of AMs during maturation. Deficiencies in bone marrow pools, complement and cytokines (IFN-gamma, TNF-alpha) as well as IgG isotype switching are known to occur in the neonate which may contribute to increased susceptibility to infection and which are amenable to immune interventions.

Host defence capacities of pulmonary surfactant: evidence for 'non-surfactant' functions of the surfactant system

The most well characterized function of pulmonary surfactant is its ability to reduce surface tension at the alveolar air-liquid interface, thereby preventing lung collapse. However, several lines of evidence suggest that surfactant may also have 'non-surfactant' functions: specific components of surfactant (proteins and phospholipids) may interact with different alveolar cells, inhaled particles and micro-organisms modulating pulmonary host defence systems. SP-A, the most abundant surfactant protein, binds to alveolar macrophages via a specific surface receptor with high affinity [128]. Such binding effects the release of reactive oxygen species from resident alveolar macrophages if SP-A is properly presented to the target cell. SP-A also stimulates chemotaxis of alveolar macrophages [142], and serves as an opsonin in the phagocytosis of herpes simplex virus [161] Candida tropicalis [138] and various bacteria [137]. In addition, SP-A enhances the uptake of particles by monocytes and culture-derived macrophages [140] and improves bacterial killing. SP-D, another hydrophobic surfactant-associated protein, might interact with alveolar macrophages as well, stimulating the release of oxygen radicals [148], while for the hydrophilic surfactant proteins SP-B and SP-C no macrophage interactions have been described so far. SP-A and SP-D are members of the so-called 'collectins', pattern recognition molecules involved in first line defence. While some surfactant proteins appear to stimulate certain macrophage defence functions, surfactant phospholipids seem to inhibit those of lymphocytes. Suppressed lymphocyte functions include lymphoproliferation in response to mitogens and alloantigens, B cell immunoglobulin production and natural killer cell cytotoxicity. Concerning surfactant's phospholipid composition phosphatidylglycerol is more suppressive than phosphatidylcholine on a molar basis [38]. Bovine surfactant has an immunosuppressive effect on the development of hypersensitivity pneumonitis in a guinea pig model [150]. Despite these interesting observations, several important questions concerning the interactions of surfactant components with pulmonary host defence systems remain unanswered. Sufficient host defence in the lungs works through various humoral-cellular systems in conjunction with the specific anatomy of the airways and the gas exchange surface--how does the surfactant system fit into this network? Surfactant and alveolar cells are both altered during lung injury--is there a relationship between alveolar cells from RDS patients and the endogenous surfactant isolated from such patients? How does exogenous surfactant as used for substitution therapy modulate the defence system of the host? Some of those artificial surfactants have been shown to inhibit the endotoxin-alveolar macrophages, PMNs and monocytes including IL-1, IL-6 and TNF [139,152].(ABSTRACT TRUNCATED AT 400 WORDS)

Pulmonary surfactant inhibits activation of human monocytes by recombinant interferon-gamma

During an inflammatory reaction in the alveoli, the functional activities of monocytes, macrophages and granulocytes are regulated by a complex network of inflammatory mediators. The primary cytokine involved in activation of these phagocytes is interferon-gamma (IFN-gamma). The possible influence of local factors, such as pulmonary surfactant, on the activation process has not been studied until now. The aim of the present study was to investigate the effects of surfactant on the activation of monocytes by recombinant (r)IFN-gamma. The results revealed that human surfactant significantly inhibited both the increase in the expression of the high-affinity receptor for IgG, i.e. Fc gamma RI, and the production of H2O2 by rIFN-gamma-activated monocytes. Since our surfactant preparation stimulated the basal production of tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) by monocytes, the effect of Survanta, a surfactant extract, on the rIFN-gamma-induced production of these cytokines by monocytes was studied. The results revealed that Survanta caused 80-90% inhibition of the rIFN-gamma-induced production of TNF-alpha and IL-1 beta by these cells. Together, these results could mean that surfactant is involved in the protection of the alveolar epithelium against injury caused by reactive oxygen intermediates (ROI) and TNF-alpha, and in the down-regulation of the production of inflammatory mediators. In view of these considerations, surfactant therapy may not only improve lung compliance and gas exchange but may also be beneficial in reducing the inflammatory reaction in the lungs.

Phospholipid analysis of alveolar macrophages and bronchoalveolar lavage fluid following bleomycin administration to rabbits

Changes in the lipid metabolism of the lung during pulmonary injury were investigated by quantitative and qualitative analysis of phospholipids in pulmonary surfactant and alveolar macrophages (AM) obtained from rabbits that had been given a single transtracheal injection of bleomycin hydrochloride (BLM) 0, 7, 14, 21, and 28 days previously. BLM treatment increased the phospholipid content of both bronchoalveolar lavage (BAL) supernatant fluids and BAL cells. Furthermore, the proportion of phosphatidylcholine (PC) showed an increase in BAL cells during the development of pulmonary injury, and BLM treatment appeared to cause transformation of AM to foamy AM. Lipid analyses of the foamy AM revealed that their phospholipid content was increased, and that the percentage of PC with palmitic acid was elevated. Thus it appears that accumulation of phospholipids derived from pulmonary surfactant contributes to the increase in phospholipids and PC in BAL cells. These findings indicate that BLM treatment produces an alteration in the amount and composition of AM phospholipids, and also in BAL supernatant fluids.

Comparison of the pulmonary surfactant content in alveolar macrophages of newborn, young, and adult rats

The phospholipid composition of the 150-g pellet containing macrophages from neonatal lung lavages resembles that of surfactant. To study whether this composition reflects the surfactant content of the macrophage, we isolated the alveolar phospholipids and macrophages from the lavage fluids of fetal, newborn, young, and adult Wistar rats. The alveolar surfactant phospholipids increased from fetal levels of 2.8 nmol/mg dry lung weight (DLW) to 39 nmol/mg DLW at day 1, decreased sharply within the first week, and stabilized at a level of 2-4 nmol/mg DLW after day 15. The number of alveolar macrophages increased significantly during the first postnatal day from approximately 750 to more than 5000 (per mg DLW), decreased during the next 4 days, and varied strongly at older ages. We estimated the surfactant content in the macrophages semiquantitatively by polarization microscopy. Birefringence augmented significantly during the first 1.5 days after birth and decreased after that concurrently with the amount of alveolar surfactant. However, only cells without birefringent inclusions sedimented at 150g, whereas the phospholipid composition of the pellets falsely suggested that large amounts of intracellular surfactant were present in its cells. At least two populations of macrophages (surfactant-rich and surfactant-poor) are present in the growing animal. We suggest that differences in function of these various types of macrophages also might depend on surfactant congestion.

Liposomes and pulmonary alveolar macrophages: functional and morphologic interactions

In vitro toxicity of liposomes and their functional and morphologic interactions with rat pulmonary alveolar macrophage (AMs) were investigated using viability (trypan blue exclusion), phagocytic and killing activity (uptake and digestion of live S. cerevisiae), surface adherence, respiratory burst (nitro-blue tetrazolium reduction), and morphometry (computerized image analysis) as indicators. Liposome stability in physiologic solutions and uptake of liposome-encapsulated carboxyfluorescein (CF) by AMs was assessed by fluorescence spectroscopy and microscopy. Liposomes made from saturated phospholipids and cholesterol were stable, whereas liposomes consisting of unsaturated phospholipids without cholesterol lost 30% to 40% of their content over 24 h. However, CF uptake was highest with unsaturated phospholipid preparations, whereas uptake of the three other formulations was comparable. Although liposome exposure did not affect macrophage viability, a reduction in the number of phagocytizing macrophages to 73% of control was noted after 24-h incubation with the highest lipid concentration tested (10 mumol/ml). Phagocytic killing was similar under all circumstances observed. The fraction of intracellularly killed yeast ranged from 32% to 42% for both control and experimental samples. An increase in cell surface area from 166.1 +/- 39.9 microns 2 on day O (n = 709) to 196.3 +/- 57.6 microns 2 on day 1 (n = 516) and 211.2 +/- 48.0 microns 2 on day 4 (n = 834) was observed after liposome treatment. The corresponding average cell areas of control samples did not change during the observation period. There was no net cell loss of adherence from monolayers as determined by protein assay. The respiratory burst, indicating generation of intracellular superoxide, was also similar--84% to 92% of experimental and control cells under all conditions showed a strong nitro-blue tetrazolium reduction. In summary, in vitro exposure of AMs to large concentrations of liposomes, although producing an increase in macrophage size, was not associated with aberrant macrophage morphologic features, function, or toxicity for the parameters examined.

Congenital syphilis in newborn rabbits: immune functions and susceptibility to challenge infection at 2 and 5 weeks of age

Experiments were performed to further elaborate on our congenital syphilis rabbit model. Attempts were made to determine whether in utero exposure to Treponema pallidum would stimulate immune reactivity and whether this activity would, in turn, affect lesion development upon challenge infection. Newborn rabbits aged 2 or 5 weeks were obtained from control does or from does infected intravenously with T. pallidum during pregnancy. Congenitally infected newborns exhibited increased immunologic functions. Concanavalin A-induced T-lymphocyte proliferation was elevated at both 2 and 5 weeks. In addition, macrophage Ia expression and RPR antibody titers were increased at 5 weeks. In separate experiments, newborn rabbits from control does or from does infected during pregnancy were challenged intradermally with viable organisms at either 2 or 5 weeks of age. Subsequent lesion severity was markedly increased in those newborns previously exposed to treponemes in utero. These observations further strengthen our model for congenital transmission of T. pallidum during pregnancy. We propose that at least some of the tissue pathology in syphilitic infection is associated with activated host defenses.

Chlamydicidal activity of human alveolar macrophages

Pneumonia due to Chlamydia trachomatis is a disease limited mainly to infants under 6 months of age. Rare cases have been reported in immunocompromised adults. One possible reason for the propensity of the pneumonia to occur in the very young may be related to differences in the phagocytic and bactericidal capacity of alveolar macrophages (AMs) in young infants and adults. At birth a function of AMs is clearance of surfactant-related material from the alveolar surface. Studies in animals have suggested that engorgement of AMs with surfactant-related lipids may reduce the microbicidal capacity of these cells. In the present study we determined that AMs obtained from healthy, nonsmoking adults were capable of killing both human biovars of C. trachomatis, with complete killing observed by 48 h after inoculation. Preincubation of AMs from adults with surfactant did not reduce the capacity of the cells to kill C. trachomatis.

Interactions between alveolar macrophage subpopulations modulate their migratory function

To better understand the mechanisms by which alveolar macrophages (AM) are attracted to local sites in the lung, the locomotion of AM in response to N-formyl-methionyl-leucyl-phenylalanine (FMLP) was investigated. Total bronchoalveolar cells (99% AM) obtained by a nondiscriminating bronchoalveolar lavage procedure migrated toward FMLP over a range of concentrations of 10(-12) M to 10(-6) M. Dose-response experiments showed a biphasic response with two peaks of migration obtained respectively at 5 x 10(-10) M and 10(-8) M. Analysis in the presence and absence of a positive gradient of FMLP revealed that the first peak of migration (5 x 10(-10) M FMLP) corresponded predominantly to chemotactic activity whereas the second peak of migration (10(-8) M FMLP) was associated with chemokinetic activity. To further evaluate these activities of oriented (chemotaxis) vs. random (chemokinesis) migration, AM were separated into two fractions by a two-step bronchoalveolar lavage procedure. Whereas fraction 1 displayed exclusively chemokinesis in response to higher concentrations of FMLP (10(-8) M), fraction 2 was totally unresponsive to FMLP over a wide range of concentrations (5 x 10(-11) M - 10(-7) M). When both fractions were combined, however, the chemotactic response to low concentrations of FMLP (5 x 10(-10) M) was restored. Additional analysis of these two AM fractions indicated that fraction 1 AM had a significantly lower degree of adherence and aggregation than fraction 2 AM. These data suggest that cell-cell cooperation is important for AM chemotactic response to FMLP and that such interaction may involve changes in adherence and aggregation.

Pulmonary surfactant inhibits priming of rabbit alveolar macrophage. Evidence that surfactant suppresses the oxidative burst of alveolar macrophage in infant rabbits

We have investigated the possible role of pulmonary surfactant in mediating a deficiency in alveolar macrophages (AM) from infant animals to produce chemiluminescent (CL) responses elicited by phorbol myristate acetate (PMA) or opsonized zymosan (Op-Zym). Freshly harvested AM from rabbits 7 to 28 days of age produced much reduced PMA-elicited CL responses compared to 5- to 6-month-old rabbits. Initially we observed that AM from both infant and adult rabbits exhibited increasing PMA- or Op-Zym-elicited CL responses in a time-dependent manner when they were incubated in RPMI 1640 medium without serum for more than 3 h. In addition, AM from infant rabbits acquired the capacity to become primed with macrophage activation factor (MAF) containing supernatants or fetal bovine serum (FBS) during an 18-h incubation period that was basically equivalent to that of AM from adult rabbits. Our studies reveal that natural and artificial surfactant inhibited "spontaneous" priming as well as priming of AM induced by MAF-containing supernatant or FBS for producing PMA- or OP-Zym-elicited CL responses from both normal infant and adult animals. In addition, these surfactant preparations also suppressed the response of AM from adult BCG-sensitized rabbits during the course of an 18-h incubation period. It is especially noteworthy that AM from infant rabbits appeared to be more susceptible to the inhibitory activity of surfactant than AM from adult animals. Our data indicate that freshly harvested AM from infant rabbits are under greater suppression than AM from adult rabbits in terms of their capacities to produce oxidative responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Mathematical analysis of cell-target encounter rates in two dimensions. The effect of chemotaxis

The process by which cells encounter their targets is the first step of a number of cell functions involved in the immune response, such as cell-mediated cytotoxicity and phagocytic ingestion of foreign material. In many instances, this encounter may be rate-limiting, and therefore it is important to understand what factors influence the encounter rate. One key aspect of cell-target encounter is the motility behavior of the cell in the vicinity of a target. This movement may be entirely random, or there may be a directed, or chemotactic, component to it. In this paper we focus on the effects of cell motility properties, and particularly the chemotactic directional bias, on the rate of cell-target encounter. Specifically, we derive an expression for the mean encounter time of cells that meet targets in two dimensions as a function of the cells' directional orientation bias. We show that a modest degree of bias can reduce the mean encounter time by orders of magnitude, while nearly perfect directional bias offers little additional benefit. We illustrate the application of these results to a particular example system: alveolar macrophages removing inhaled particles and bacteria from the lung surface.

Functional and ultrastructural changes in alveolar macrophages from rabbits colonized with Bordetella bronchiseptica

Alveolar macrophages from rabbits colonized with Bordetella bronchiseptica in their respiratory tract exhibited significant decreases in cell adherence, phagocytic uptake, and bactericidal activity compared with macrophages from uncolonized animals. These dysfunctions were accompanied by ultrastructural changes, including a decrease in overall cell density, a vacuolation of the rough endoplasmic reticulum, and an increase in organelle-poor cell surface projections.

Host-parasite relationship in opportunistic mycoses

Aspergillosis and mucormycosis are opportunistic fungal infections that share several unique features. The etiologic agents of aspergillosis and mucormycosis are ubiquitous in the environment, but are opportunistic organisms and usually infect only patients predisposed by some underlying disease or treatment. These infections are typically characterized by hyphal tissue invasion and a predilection of the organism for blood vessel invasion with hemorrhage, necrosis, and infarction. Also, these organisms are not dimorphic, like the true pathogenic dimorphic fungi, as they grow both in the environment and within the host in hyphal forms. However, the host must contend with several forms to successfully eliminate them. Each form displays different antigenic and surface features and elicits different host responses. Finally, if germination and hyphal growth occur, the host must compete with a rapidly growing organism that is too large to be ingested by a single cell and so must be handled by extracellular defense mechanisms.