The fungicidal mechanisms of human monocytes. I. Evidence for myeloperoxidase-linked and myeloperoxidase-independent candidacidal mechanisms

Early defect of phagocytic cell function in subjects at risk for acquired immunodeficiency syndrome

We studied the functions of peripheral blood monocytes and polymorphonuclear cells in 15 apparently healthy homosexual men, eight homosexual or bisexual subjects with unexplained generalized lymphadenopathies (pre-AIDS), four homosexual men with acquired immunodeficiency syndrome (AIDS), and 15 heterosexual men. In comparison with normal controls, the homosexual groups studied presented a decreased monocyte candidacidal activity for Candida pseudotropicalis that gradually deteriorates as the clinical symptoms progress towards AIDS. The monocyte phagocytic function was retained. Although the phagocytic and candidacidal activities of the polymorphonuclear cells did not differ from those of the normal controls, the candidacidal activity in some of the cases studied was unusually enhanced, indicating that the cells were in an activated state. In addition, only two of nine sera tested from asymptomatic homosexual males were positive for antibodies to HTLV-III/LAV, while six out of eight pre-AIDS and both of the two AIDS patients tested had antibodies to AIDS-associated retrovirus. We suggest that in AIDS the phagocytic system is already involved, together with B and T lymphocyte abnormalities, during the early events of the syndrome, even without the detection of AIDS-associated retrovirus antibodies.

In vitro susceptibility of fungi to killing by neutrophil granulocytes discriminates between primary pathogenicity and opportunism

Pathogenic fungi, according to their propensity to cause infection of apparently normal individuals, can be grouped into either primary pathogens (e.g., Coccidioides, Histoplasma, Paracoccidioides, Blastomyces, and Sporothrix) or opportunists (e.g., Candida, Mucoraceae, Aspergillus spp., Petriellidium, and Trichosporon). There is, however, no unifying concept explaining the difference between the virulence of the two fungal categories. Previously we have speculated that neutrophils are the common denominator of the high natural resistance to opportunistic fungi. Accordingly, we then compared the susceptibility to killing by neutrophil granulocytes of Histoplasma, Blastomyces, Paracoccidioides, and Sporothrix with that of 14 opportunistic fungi. We found the four virulent dimorphic yeasts, in contrast to opportunistic fungi, to be resistant to killing by neutrophils. Virulent dimorphic yeasts were ingested by neutrophils, and triggered a respiratory burst comparably to opportunists but were less susceptible to hydrogen peroxide, suggesting that differences in the susceptibility to microbicidal products of leukocytes may explain the difference in virulence.

Primary Candida meningitis and chronic granulomatous disease

The occurrence of two rare entities in a single patient can be fortuitous or may signify some deeper relationship. A young boy was recently treated for primary Candida meningitis. Autopsy findings suggested to an experienced pathologist the presence of chronic granulomatous disease (CGD), unrecognized during his life. The patient's identical twin brother was tested and found to have the typical laboratory features of CGD. The literature on Candida meningitis was reviewed and 15 cases were discovered that apparently arose in the absence of recognized predisposing causes. All but one of these cases occurred in males, and most occurred during the first three decades of life. The case reports and literature review presented herein suggest that CGD should be suspected when a case of "primary" Candida meningitis is encountered.

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.

Rapid killing of monocytes in vitro by Candida albicans yeast cells

To study the interaction between Candida albicans blastoconidia and human phagocytes, we incubated peripheral leukocytes with fungi for 1 h at 37 degrees C and stained the cells with fluorescent vital stains ethidium bromide (EB) and fluorescein diacetate. Fungi that had been phagocytosed showed little staining; however, some leukocytes containing blastoconidia exhibited nuclear staining with EB, even though their cell membranes showed no signs of penetration by fungi. The number of EB-positive leukocytes was related to viability of the yeast cells and the temperature at which they were maintained before use. Because efforts to quantitate EB-positive leukocytes microscopically were frustrated by cell aggregation, we labeled the leukocytes with 51Cr and measured isotope release. We determined that leukocytes incubated with viable fungi released significantly more isotope than cells incubated alone or with killed blastoconidia. Furthermore, 51Cr release correlated directly with concentration of fungi in the assay, time of incubation, and temperature at which fungi were maintained before use. Using a number of isolates of C. albicans and several other species of Candida, we found that all exhibited cytotoxic activity against leukocytes, but the level of activity varied among organisms. Finally, we depleted or enriched peripheral leukocytes for specific cell populations and determined that only monocytes released more 51Cr after incubation with viable blastoconidia. Blastoconidia can lyse phagocytic cells through germination and penetration of cell membranes within 1 to 2 h, but the cytotoxic phenomenon we describe occurs within 15 to 30 min after yeast cells have been phagocytosed. Therefore, this capacity may represent a more immediate response by blastoconidia against phagocytosis and killing by monocytes.

Normalization of monocyte candidacidal deficiency by cyclooxygenase inhibitors in Hodgkin's disease

In a previous work, the authors found that the peripheral blood monocytes from patients with Hodgkin's disease (HD) had depressed lytic capability to kill Candida pseudotropicalis and depressed phagocytic function. The aim of this study was to evaluate if cyclooxygenase inhibitors could correct the defective macrophage functions. Fifteen untreated patients with HD and 10 normal subjects were studied. The incubation of the cells from the patients with HD with indomethacin (IM) at 1, 3, and 10 micrograms/ml and with acetylsalicylic acid (ASA) at 20 micrograms/ml increased their previously deficient ability to kill C. pseudotropicalis, reaching values close to those of normal subjects. The oral administration of ASA during 1 week also corrected the monocyte lytic deficiency in the patients' group. Neither the in vitro nor the in vivo treatment with these cyclooxygenase inhibitors had any significant effect on normal subjects' monocytes' lytic function. The drugs did not improve the impaired phagocytic function in patients with HD. These results indicate that the failure of the lytic activity of the monocytes in HD could be associated to an excessive production of PGE2, and the oral administration of inhibitors of the cyclooxygenase activity can correct such abnormality whereas the phagocytic dysfunction is not reverted by them.

Role of lipoprotein-X in the pathogenesis of cholestatic hypercholesterolemia. Uptake of lipoprotein-X and its effect on 3-hydroxy-3-methylglutaryl coenzyme A reductase and chylomicron remnant removal in human fibroblasts, lymphocytes, and in the rat

Cholestasis is accompanied by the appearance of lipoprotein-X (LP-X) in plasma. This lipoprotein has a high content of unesterified cholesterol and phospholipids and appears to be ineffective in suppressing the enhanced hepatic cholesterogenesis of cholestasis. Its role as a possible causative factor for cholestatic hypercholesterolemia was investigated. When 125I-LP-X was injected into rats, it disappeared rapidly from the circulation. Calculated on the basis of gram wet weight, spleen took up more LP-X than liver. Prior ligation of the bile duct reduced the uptake in spleen. Experiments with isolated perfused rat liver showed that nonparenchymal cells (NPC) took up over eightfold more 125I-LP-X than hepatic parenchymal cells (PC). Incubation of PC, NPC, human lymphocyte suspensions, or fibroblast cultures with LP-X showed that NPC bound more LP-X than PC or fibroblasts. Lymphocytes took up 20-fold more LP-X than PC and the activity of 3-hydroxy-3-methylglutaryl Coenzyme A (HMG-CoA) reductase was depressed by LP-X. Lymphocytes isolated from cholestatic patients showed low activity of this enzyme. The activity was increased by LP-X in isolated perfused livers, but suppressed in isolated microsomes. LP-X competitively inhibited the uptake of chylomicron remnants in isolated perfused livers and hepatocytes. In contrast, degradation of LDL by perfused livers, which were isolated from ethinyl estradiol-treated rats or human fibroblast cultures, remained unchanged in the presence of LP-X. The results indicate that cholesterol transported by LP-X is mainly taken up by the cells of the reticuloendothelial system. It increases the activity of hepatic HMG-CoA reductase and suppresses remnant uptake, thus emphasizing a major role of LP-X in cholestatic hypercholesterolemia.

Protecting effect of chitin and chitosan on experimentally induced murine candidiasis

Chitin and chitosan were found to exhibit a protective effect on mice administered these polysaccharides intraperitoneally against infection of the viable cells of Candida albicans NIH A-207 strain. A significant difference was observed between the protective effects of chitin and chitosan, i.e., chitin was much more effective than chitosan when the C. albicans cells were challenged via the intravenous route. In intraperitoneal inoculations of C. albicans cells, however, chitosan provided stronger resistance for mice than chitin. It has also been revealed that the number of polymorphonuclear leukocytes from circulating blood of chitin-administered mice increased remarkably compared with that of untreated and chitosan-treated mice, and that the increase of active oxygen-generating phagocytic cells was significant. On the other hand, the number of peritoneal exudate cells (PEC) and the amounts of active oxygen generated from these cells in chitosan-treated mice were larger than those of chitin-treated mice. However, candidacidal activities of PEC per fixed cell number in mice treated with chitin or with chitosan were almost the same and greater than those of untreated mice.

Susceptibility of Blastomyces dermatitidis strains to products of oxidative metabolism

Three strains of Blastomyces dermatitidis which differ in their virulence for mice were exposed in their yeast form to various components of the peroxidase-hydrogen peroxide-halide system. Susceptibility to H2O2 alone correlated with virulence, with the most virulent strain (ATCC 26199) least susceptible (50% lethal dose, greater than 50 mM) and an avirulent strain (ATCC 26197) most susceptible (50% lethal dose less than 3.3 mM). A strain of intermediate virulence (ATCC 26198) was of intermediate susceptibility (50% lethal dose, 11.5 mM). The addition of a nontoxic concentration of KI (5 X 10(-4) M) did not increase H2O2 toxicity. However, the addition of either myeloperoxidase or horseradish peroxidase and KI markedly decreased the amount of H2O2 required to kill the organisms, with 100 +/- 0% of all strains killed at 5 X 10(-5) M H2O2 and 97 +/- 4, 100 +/- 0, and 94 +/- 8% of ATCC 26199, ATCC 26198, and ATCC 26197 killed, respectively, at 5 X 10(-6) M H2O2. Kinetic studies with H2O2 alone revealed a delayed onset of killing, but virtually 100% of organisms were killed by 120 min of exposure in all strains. By comparison, the peroxidase-hydrogen peroxide-halide system was 100% lethal for all strains at 1 min. The relatively high concentrations of H2O2 required to kill the yeast phase of B. dermatitidis suggest that H2O2 alone does not account for host resistance to the organism. However, the rapidly lethal effect of the peroxidase-hydrogen peroxide-halide system at physiologically relevant concentrations suggests that this may be one mechanism of host defense to B. dermatitidis.

Killing of intracellular Leishmania donovani by human mononuclear phagocytes. Evidence for oxygen-dependent and -independent leishmanicidal activity

Human peripheral blood monocytes were cultivated for 1-30 d before assay for H2O2 release or challenge with Leishmania donovani promastigotes (LDP) or amastigotes (LDA). 1-d cells readily generated H2O2 in response to both phorbol myristate acetate triggering (1,013 +/- 58 nmol/mg protein . 90 min) and LDP ingestion, and killed 50% of LDP within 6 h, and 90% by 24 h. In contrast, the same cells released little H2O2 during LDA ingestion, killed no LDA at 6 h and less than 30% by 24 h, and supported intracellular LDA replication. Monocyte-derived macrophages (cells first cultivated for greater than or equal to 7 d) generated less than 125 nmol H2O2/mg . 90 min after phorbol myristate acetate triggering, killed neither LDP nor LDA, and permitted both forms to replicate. The addition of mitogen- or antigen-stimulated lymphokines, however, prevented the decline in monocyte oxidative capacity, enhanced macrophage H2O2 release by more than sixfold, and, in parallel, induced 1-d monocytes to kill LDA and cultivated macrophages to display both promastigocidal and amastigocidal activity. In comparison to 1-d monocytes and lymphokine-activated macrophages from normal donors, the same cells from patients with chronic granulomatous disease (CGD) or normal cells whose oxidative activity had been impaired by catalase pretreatment or glucose deprivation exerted considerably less or no antileishmanial activity during the early (6-24 h) postphagocytic period. By 48 h after infection, however, 1-d CGD monocytes and oxidatively impaired normal cells killed 40 and greater than 80% of LDP, respectively. Although a longer period of lymphokine stimulation was required and the resulting antileishmanial effects were not as rapid as with normal cells, activated CGD monocytes and macrophages also eventually achieved promastigocidal and amastigostatic activity. These results indicate that human mononuclear phagocytes utilize both oxygen-dependent and -independent mechanisms to achieve activity against ingested Leishmania, and also demonstrate (a) the differential susceptibilities of the two forms of L. donovani to intracellular killing, (b) the key role of oxygen intermediates in effective mononuclear phagocyte antimicrobial activity, (c) the capacity of lymphocyte products to enhance oxygen-dependent as well as -independent pathways, and (d) the vulnerability of the monocyte-derived macrophage to Leishmania infection in the absence of lymphokine stimulation.

Candidal antigen detection in pulmonary candidiasis

To better characterize pulmonary candidiasis, lung tissue samples from 58 hospital subjects were examined by immunohistochemical analysis with antiserums to candidal mannan and cytoplasmic antigens. In nine cases of invasive pulmonary candidiasis, fungal antigens were abundant in lung specimens and were distributed in two immunohistologic patterns. Antigen dissemination beyond the lung was confirmed by detection of antigenemia by mannan radioimmunoassay in serum samples in cases of pulmonary candidiasis of each immunohistologic pattern. In contrast, minimal, focal quantities of fungal antigens were detected in lung tissue specimens from nine subjects with thrush or aspiration but without pulmonary candidiasis; no antigen was detected in 40 additional cases of noncandidal mycotic, bacterial, viral, and parasitic pneumonias. Immunohistochemical criteria that denote invasive pulmonary candidiasis include the abundance of diffuse candidal antigens in bronchiolar and alveolar fluid and cytoplasmic staining of phagocytes. When compared with routine histologic stains, the diagnostic yield in cases of invasive pulmonary candidiasis was significantly increased by detection of candidal antigenic material. This study of 58 well-documented cases shows that immunohistochemical detection of candidal antigens facilitates the diagnosis of candidal pneumonia and distinguishes clinically significant pulmonary candidiasis from noninvasive aspiration, opportunistic colonization, or specimen contamination.

The enhancement of eosinophil function by lymphocyte supernatants

Supernatants obtained from non-stimulated lymphocytes, lymphocytes stimulated with phytohaemagglutinin and lymphocytes from patients with schistosomiasis that were stimulated with Schistosomiasis haematobium ova were shown to enhance a number of eosinophil functions. Eosinophil chemotaxis, phagocytosis, microbicidal activity, Nitro blue tetrazolium reduction, hexose monophosphate shunt activity and glycolysis were increased. Eosinophil iodination was not affected. Only those supernatants obtained from phytohaemagglutinin stimulated lymphocytes and lymphocytes from patients with schistosomiasis that were stimulated with S. haematobium ova showed eosinophil chemotactic activity. The active factor was found to be heat stable, and had no effect on cAMP and cGMP metabolism. The most likely mechanism of enhanced eosinophil function is through the increased activity of the hexose monophosphate shunt activity and glycolysis.

Damage to Aspergillus fumigatus and Rhizopus oryzae hyphae by oxidative and nonoxidative microbicidal products of human neutrophils in vitro

Our previous studies established that human neutrophils could damage and probably kill hyphae of Aspergillus fumigatus and Rhizopus oryzae in vitro, primarily by oxygen-dependent mechanisms active at the cell surface. These studies were extended, again quantitating hyphal damage by reduction in uptake of (14)C-labeled uracil or glutamine. Neither A. fumigatus nor R. oryzae hyphae were damaged by neutrophils from patients with chronic granulomatous disease, confirming the importance of oxidative mechanisms in damage to hyphae. In contrast, neutrophils from one patient with hereditary myeloperoxidase deficiency damaged R. oryzae but not A. fumigatus hyphae. Cell-free, in vitro systems were then used to help determine the relative importance of several potentially fungicidal products of neutrophils. Both A. fumigatus and R. oryzae hyphae were damaged by the myeloperoxidase-hydrogen peroxide-halide system either with reagent hydrogen peroxide or enzymatic systems for generating hydrogen peroxide (glucose oxidase with glucose, or xanthine oxidase with either hypoxanthine or acetaldehyde). Iodide with or without chloride supported the reaction, but damage was less with chloride alone as the halide cofactor. Hydrogen peroxide alone damaged hyphae only in concentrations >/=1 mM, but 0.01 mM hypochlorous acid, a potential product of the myeloperoxidase system, significantly damaged R. oryzae hyphae (a 1 mM concentration was required for significant damage to A. fumigatus hyphae). Damage to hyphae by the myeloperoxidase system was inhibited by azide, cyanide, catalase, histidine, and tryptophan, but not by superoxide dismutase, dimethyl sulfoxide, or mannitol. Photoactivation of the dye rose bengal resulted in hyphal damage which was inhibited by histidine, tryptophan, and 1,4-diazobicyclo(2,2,2)octane. Lysates of neutrophils or separated neutrophil granules did not affect A. fumigatus hyphae, but did damage R. oryzae hyphae. Similarly, three preparations of cationic proteins purified from human neutrophil granules were more active in damaging R. oryzae than A. fumigatus hyphae. This damage, as with the separated granules and whole cell lysates, was inhibited by the polyanion heparin. Damage to R. oryzae hyphae by neutrophil cationic proteins was enhanced by activity of the complete myeloperoxidase system or by hydrogen peroxide alone in subinhibitory concentrations. These data support the importance of oxidative products in general and the myeloperoxidase system in particular in damage to hyphae by neutrophils. Cationic proteins may also contribute significantly to neutrophil-mediated damage to R. oryzae hyphae.

Monocyte-mediated damage to Rhizopus oryzae hyphae in vitro

Clinicopathological correlations from human cases and experimental animal studies suggest that neutrophils are critical components of the host response to mucormycosis but that other cellular defense mechanisms appear to be important as well. Since our previous studies demonstrated that Rhizopus oryzae hyphae which are too large to be ingested completely can be damaged and probably killed by human neutrophils, we studied the antihyphal activity of human monocytes. As with neutrophils, light and electron microscopic studies indicated that monocytes attached to hyphae and appeared to destroy them in the absence of serum. As judged by our previously described assay for the leukocyte-induced inhibition of [14C]uracil uptake by hyphae, quantitative damage to hyphae by monocytes was 40.8 +/- 2.2% in 54 experiments. Neither attachment to nor damage of hyphae by monocytes was augmented by the presence of 10% human serum. As with neutrophils, monocyte-mediated damage of R. oryzae was significantly decreased by some inhibitors of oxidative metabolism and scavengers of the potentially microbicidal oxidative leukocyte products, which included 10(-4)M sodium azide, 10 (-3) M sodium cyanide, catalase, 10(-3) M histidine, 10(-3) M tryptophan, and 10(-4) M 1,4-diazobicyclo[2.2.2]octane but not superoxide dismutase, 1.4 X 10(-2) M dimethyl sulfoxide, and 4.0 X 10(-1) M mannitol. Moreover, monocytes from three patients with chronic granulomatous disease failed to damage hyphae at all. In contrast to our previous data for neutrophils, polyanions (10(-5) M polyaspartic or polyglutamic acid) did not inhibit monocyte-mediated hyphal damage. Thus, monocytes can damage and probably kill R. oryzae hyphae by oxidative mechanisms and so may be involved in host defense mechanisms against mucormycosis.

Small-scale isolation and characterisation of human peripheral blood monocytes

A technique is described for the isolation and characterisation of monocytes from 15 ml of human peripheral blood. After density gradient centrifugation over Ficoll-Hypaque, monocytes are purified further by substrate adherence under carefully defined conditions. The use of a simple microwell slide system permits the production of multiple small-scale monolayer populations which can be characterised further in terms of their histochemical reactivity (combined stain for chloroacetate and non-specific esterases); endocytic capacity (latex particles); Fc (sensitised ox erythrocytes) and C3 (serum-coated yeast) receptor expression; and precursor maturation potential (7-day cultures). Evidence of considerable cellular heterogeneity is presented.

Discoid lupus erythematosus-like lesions and stomatitis in female carriers of X-linked chronic granulomatous disease

The skin and oral mucosa were studied in an unselected series of carriers of x-linked chronic granulomatous disease, a hereditary condition in which phagocytic cells display a pronounced functional defect. Three carriers had discoid lupus erythematosus (DLE)-like skin lesions which histopathologically were consistent with DLE of the hypertrophic and profundus type. Four patients had experienced photosensitivity in childhood. Seven patients had recurrent aphthous-like stomatitis which should be distinguished from the recurrent aphthous stomatitis seen in otherwise healthy individuals. The remarkably high incidence of DLE-like symptoms in heterozygous carriers might be related to the presence of mixed populations of defective and normal phagocytes. The variable expression of skin symptoms may be related to uneven distribution of abnormal and normal phagocytes. Female patients with these clinical symptoms, especially the combination of DLE-like skin lesions and aphthous-like stomatitis, should be suspected of being carriers of chronic granulomatous disease and studies of phagocyte function in vitro should be performed, since the diagnosis of the carrier state is of utmost importance for genetic counselling before pregnancy.

Effect of mouse phagocytes on Candida albicans in in vivo chambers

Mouse phagocytic cells in in vivo diffusion chambers had either candidacidal or candidastatic activity depending on the kind of phagocyte studied, the type of mouse whence the phagocytes came, and whether the chamber inoculum of Candida albicans consisted primarily of yeasts or hyphae. Killing of C. albicans occurred when yeasts were placed into chambers with membranes with 3.0-micrometer pores and implanted intraperitoneally into normal mice or thymus-deficient (nude) mice. Although C. albicans remains in chambers with 3.0-micrometer pores, host phagocytic cells can migrate into the chambers. Killing also occurred when yeasts were combined with normal or nude mouse neutrophils in chambers made with membranes with 0.45-micrometer pores, which restrict migration of host cells, but not diffusion of soluble factors. Populations of cells rich in macrophages were candidastatic for yeasts when the phagocytes came from normal mice but candidacidal when obtained from nude mice. Results of gradient fractionations of peritoneal exudates indicated that more than one cell type may be responsible for candidacidal activity by nude mouse macrophage-rich cells. Hyphal-phase cells of C. albicans appear to be more resistant than yeast-phase cells to killing by normal and nude mouse phagocytic cells.

Monocyte-mediated serum-independent damage to hyphal and pseudohyphal forms of Candida albicans in vitro

Human peripheral blood monocytes attached to Candida albicans hyphae in the absence of serum and damaged the hyphae without completely ingesting them. Attachment and damage was not augmented by the addition of serum. Damage to hyphae was quantitated by a previously developed metabolic assay that measured leukocyte-induced reduction in uptake of [(14)C]cytosine by the hyphae. Use of cells from patients with hereditary disorders of leukocyte function, chronic granulomatous disease, and myeloperoxidase deficiency indicated that myeloperoxidase-independent and nonoxidative mechanisms could sometimes damage hyphae where oxidative mechanisms were impaired. Damage to hyphae by normal monocytes was inhibited by concentrations of sodium azide and sodium cyanide that primarily affect myeloperoxidase activity, as well as by halide-free conditions, catalase, and putative antagonists of hypochlorous acid or singlet oxygen. Iodination of hyphae, a myeloperoxidase and hydrogen peroxide-dependent process of monocytes, was similarly inhibited by sodium azide, sodium cyanide, and catalase. Under anaerobic conditions, damage to hyphae was reduced by 64.0-68.4%. In contrast, inhibitors of potential nonoxidative antifungal mechanisms, iron salts to saturate iron chelators, and polyanionic amino acid polymers to neutralize cationic proteins did not block damage to hyphae by monocytes. Preparations rich in lysosomal granules from fractionated normal monocytes also did not damage hyphae. Overall, it appeared that oxidative mechanisms were most important for damage to hyphae by normal monocytes. Electron microscopy confirmed that Candida hyphae were damaged and probably killed by monocytes, but monocytes appeared to sustain significant damage in the process. In the absence of serum, monocyte cell membranes became closely approximated to Candida cell walls. It appeared that some Candida could escape this partial engulfment, as they were seen floating free with vesicular trilaminar membrane remnants covering hyphal surfaces. In general, monocytes appeared to be damaged by interactions with Candida hyphae more than neutrophils had been in previous studies.

Activation of macrophages for enhanced release of superoxide anion and greater killing of Candida albicans by injection of muramyl dipeptide

The adjuvant muramyl dipeptide (MDP) has been shown to affect a number of macrophage functions in vitro. We studied the effect of subcutaneous injection of MDP into mice. Cultured peritoneal macrophages from treated mice displayed increased spreading, total cell protein, and specific activity of beta-glucosaminidase a constituent of macrophage lysosomes, and of lactate dehydrogenase. Generation of superoxide anion (O2-) by MDP-treated macrophages stimulated by contact with phorbol myristate acetate was enhanced by over fivefold to levels achieved by macrophages from bacillus Calmette-Guérin-infected mice. The enhancement in stimulated O2- release was noted by 1 h after injection of MDP, peaked by 3 h, and remained high for at least 48 h. Priming for enhancement of O2- release by MDP was similar in athymic nude mice and in normal littermates, suggesting that mature T lymphocytes are not involved in this MDP effect. Priming for enhanced stimulated O2- release, and morphologic and enzymic changes, were not achieved by injection of the D-D stereoisomer of MDP. Phagocytosis of Candida albicans was only slightly greater by macrophages from mice give MDP, but MDP-stimulated cells killed two times more C. albicans in vitro than did cells from untreated animals. When MDP was given 18 h before, simultaneously with, or 24 h after lethal infectious challenge with C. albicans, treated mice were protected compared with controls. These results suggest that injection of MDP effectively and rapidly activates macrophages in the recipient animal. This agent should serve as an important probe of macrophage physiology and, perhaps ultimately, as a means of enhancing host defense in humans.

Damage to Candida albicans hyphae and pseudohyphae by the myeloperoxidase system and oxidative products of neutrophil metabolism in vitro

In previous studies, we noted that Candida hyphae and pseudohyphae could be damaged and probably killed by neutrophils, primarily by oxygen-dependent nonphagocytic mechanisms. In extending these studies, amount of damage to hyphae again was measured by inhibition of [(14)C]cytosine uptake. Neutrophils from only one of four patients with chronic granulomatous disease damaged hyphae at all, and neutrophils from this single patient damaged hyphae far less efficiently than simultaneously tested neutrophils from normal control subjects. Neutrophils from neither of two subjects with hereditary myeloperoxidase deficiency damaged the hyphae. This confirmed the importance of oxidative mechanisms in general and myeloperoxidase-mediated systems in particular in damaging Candida hyphae. Several potentially fungicidal oxidative intermediates are produced by metabolic pathways of normal neutrophils, but their relative toxicity for Candida hyphae was previously unknown. To help determine this, cell-free in vitro systems were used to generate these potentially microbicidal products. Myeloperoxidase with hydrogen peroxide, iodide, and chloride resulted in 91.2% damage to hyphal inocula in 11 experiments. There was less damage when either chloride or iodide was omitted, and no damage when myeloperoxidase was omitted or inactivated by heating. Azide, cyanide, and catalase (but not heated catalase) inhibited the damage. Systems for generation of hydrogen peroxide could replace reagent hydrogen peroxide in the myeloperoxidase system. These included glucose oxidase, in the presence of glucose, and xanthine oxidase, in the presence of either hypoxanthine or acetaldehyde. In the presence of myeloperoxidase and a halide, the toxicity of the xanthine oxidase system was not inhibited by superoxide dismutase and, under some conditions, was marginally increased by this enzyme. This suggested that superoxide radical did not damage hyphae directly but served primarily as an intermediate in the production of hydrogen peroxide. The possible damage to hyphae by singlet oxygen was examined using photoactivation of rose bengal. This dye damaged hyphae in the presence of light and oxygen. The effect was almost completely inhibited by putative quenchers of singlet oxygen: histidine, tryptophan, and 1,4-diazobicyclo[2.2.2]octane. These agents also inhibited damage to hyphae by myeloperoxidase, halide, and either hydrogen peroxide or a peroxide source (xanthine oxidase plus acetaldehyde). Myeloperoxidase-mediated damage to hyphae was also inhibited by dimethyl sulfoxide, an antioxidant and scavenger of the hydroxyl radical. These data support the involvement of oxidative mechanisms and the myeloperoxidase-H(2)O(2)-halide system, in particular in damaging hyphae in vitro and perhaps in vivo as well.

Microbicidal cationic proteins in rabbit alveolar macrophages: a potential host defense mechanism

Rabbit alveolar macrophages contain two highly cationic microbicidal proteins. These were shown to be distinct from histones and not to arise from granulocyte contamination. The macrophage proteins were especially active against Candida albicans and Candida parapsilosis. Gram-positive bacteria (Bacillus subtilis, Listeria monocytogenes, and Streptococcus faecalis) were also susceptible, whereas Escherichia coli and Salmonella typhimurium appeared more resistant. The proteins may be present in lysosomes, based on their solubilization by dilute acids and their distribution with lysosomal markers on sucrose density gradients. Such microbicidal proteins have not previously been demonstrated in any mammalian macrophage. They may play a significant role in the host-defense functions of the rabbit lung.

Impaired monocyte-mediated cytotoxicity in atopic dermatitis

Twenty-three adult patients with atopic dermatitis of different severity and extent all without present cutaneous infection were investigated for antibody-dependent cytotoxicity mediated by purified monocytes. Compared to a healthy control group the monocyte cytotoxicity was significantly decreased for patients with more widespread dermatitis. Eight patients with acute contact dermatitis and 13 patients with extrinsic asthma or allergic rhinitis showed normal cytotoxicity. Decreased monocyte cytotoxicity in atopic dermatitis was not related to the serum IgE level. In vitro cultivation of defective monocytes from atopics did not increase cytotoxicity, nor did normal monocytes preincubated with patient serum show abnormal function. In atopic dermatitis the total number of Fc receptor bearing monocytes was normal. However, the affinity of this receptor was lower than in normals. Serial studies are needed to establish whether reduced monocyte function is a basic pathophysiologic defect in atopic dematitis.

Defective function of peripheral blood monocytes in patients with Hodgkin's and non-Hodgkin's lymphomas

Phagocytosis and lysis of C. pseudotropicalis by peripheral blood monocytes from Hodgkin's and non-Hodgkin's lymphoma were analysed. In Hodgkin's disease, there was a decrease in the phagocytic activity of blood monocytes; moreover, the candidacidal activity was significantly decreased as compared with normal controls. Although monocytes from non-Hodgkin's patients presented normal phagocytic function, the ability to kill C. pseudotropicalis was impaired. In both groups of lymphomas, the data showed that the abnormal findings were not related to treatment. These results indicate that monocytes from Hodgkin's and non-Hodgkin's lymphoma posses a deficiency in killing C. pseudotropicalis, which could be due to an intrinsic macrophage defect in the myeloperoxidase-independent mechanisms and which may be responsible for the predisposition of the se patients to candida infections.

Macrophage microbicidal activity. Correlation between phagocytosis-associated oxidative metabolism and the killing of Candida by macrophages

The mechanisms by which macrophages kill ingested microorganisms were explored using Candida albicans and Candida parapsilosis. The results indicate that efficient macrophage candidacidal activity depends upon the generation of oxygen metabolites by the phagocytic cell: (a) peritoneal macrophages from mice infected with bacillus Calmette-Guerin (BCG) or injected intraperitoneally with lipopolysaccharide (LPS) released more superoxide anion (0(2)(-)) during phagocytosis of candida and killed candida better than did resident macrophages; (b) cells of the macrophage-like line J774.1, which released negligible amounts of O(2)(-), could ingest the candida normally but not kill them; (c) killing of candida by resident, LPS- elicited, and BCG-activated macrophages was inhibited by agents that scavenge O(2)(-), hydrogen peroxide (H(2)0(2)), hydroxyl radical (x OH), and singlet oxygen; and (d) all three macrophage types killed C. parapsilosis more effectively than C. albicans, and (7. parapsilosis stimulated a more prompt and vigorous burst of macrophage oxygen consumption and 0(2)(-) release than did C. albicans. Macrophages ingested C. parapsilosis slightly more quickly than C. albicans, but phagocytosis of both strains was equivalent by 60 min of incubation. Although C. albicans contained higher concentrations of the oxygen-metabolite scavengers superoxide dismutase and catalase, neither fungal species scavenged 0(2)(-) or H(2)0(2) effectively; and C. albicans was killed more easily than C. parapsilosis by a xanthine oxidase system that generates primarily H(2)O(2) at pH 7, or 0(2)(-) and x OH at pH 10. Thus, the decreased killing of C. albicans appears to result primarily from the capability of this species to elicit less vigorous stimulation of macrophage oxidative metabolism. This capability may have general relevance to the pathogenicity of microorganisms.

In vitro susceptibility testing of Paracoccidioides brasiliensis to sulfonamides

A total of 60 clinical isolates of Paracoccidioides brasiliensis were tested for susceptibility to sulfadiazine and sulfadimethoxyne by the agar dilution technique. A modification of the Mueller-Hinton medium was devised which gave good growth of the yeast form. The minimum inhibitory concentrations for only 51.6% of the isolates were in the range of the recommended blood serum concentration (50 micrograms/ml). For 6 to 8% of the isolates, the minimum inhibitory concentrations were above 200 micrograms of both sulfadiazine and sulfadimethoxyne per ml. A significant decreases in susceptibility was demonstrated for one isolate obtained from a patient relapsing during sulfonamide therapy.

In vitro phagocytosis of Candida albicans by peritoneal mouse macrophages

The ability of sensitized mouse peritoneal macrophages to phagocytose and inhibit Candida albicans was studied in an in vitro system. Mice were sensitized to C. albicans by intraperitoneal infection with viable organisms or by intracutaneous injection of heat-inactivated cells in Freund complete adjuvant. Development of delayed hypersensitivity to C. albicans was evaluated by footpad tests with cytoplasmic and cell wall antigens as well as by macrophage migration inhibition by these antigens and by whole heat-inactivated cells. Inhibition of macrophage migration by heat-inactivated cells was significantly greater when the mice were sensitized by viable organisms. The macrophages from these mice were also larger and showed a greaer ability to inhibit germ tube production by phagocytosed yeasts. This suggests that macrophages may play a protective role in infection by C. albicans.

Fungicidal activity of rabbit alveolar and peritoneal macrophages against Candida albicans

We tested the ability of rabbit macrophages to kill Candida albicans in vitro. Resident (unstimulated) alveolar macrophages killed 28.1 +/- 1.9% of ingested organisms in 4 h, whereas resident peritoneal macrophages killed only 15.2 +/- 1.3% (mean +/- standard error of the mean, P < 0.01). Peritoneal macrophages obtained from rabbits treated 3 weeks earlier with complete Freund adjuvant showed enhanced candidacidal activity relative to normally resident peritoneal cells (28.2 +/- 3.1%, P < 0.01). Candidacidal activity by alveolar macrophages recovered from such treated animals was slightly enhanced relative to untreated alveolar macrophages (32.9 +/- 2.3%). Candidacidal activity by peritoneal and alveolar macrophages was not decreased by several agents (cyanide, azide, sulfadiazine, and phenylbutazone) that inhibit the ability of human blood monocytes to kill C. albicans. In contrast, candidacidal activity by alveolar macrophages was greatly diminished by iodoacetate, an ineffective inhibitor of this function in human monocytes. We conclude that rabbit macrophages kill C. albicans by a fungicidal mechanism distinct from the peroxidase-H2O2 mechanism of human granulocytes and monocytes, and that the fungicidal properties of peritoneal and alveolar macrophage populations are enhanced after nonspecific stimulation with complete Freund adjuvant.

Phagocytosis in acute leukemia

The phagocytic potential of leukemic cells in various types of acute leukemia was studied. Cases included lymphoblastic leukemia, myeloblastic leukemia, myelomonocytic leukemia, monocytic leukemia, progranulocytic leukemia, blast transformation of chronic myelocytic leukemia, and unclassified leukemias. Cytochemical stains were used as an aid in classification. These included Sudan black B, naphthol AS-D chloroacetate esterase, alpha-naphthyl butyrate esterase, acid phosphatase, and periodic acid-Schiff. Phagocytosis was evaluated after incubation of leukemic cells with Candida albicans. Rare phogocytic activity was seen in lymphoblastic leukemia, unclassified leukemias, blast crises in chronic myelocytic leukemia, and progranulocytic leukemia. Myeloblastic leukemias were feebly phagocytic. Myelomonocytic leukemia and monocytic leukemia both exhibited marked phagocytosis which distinguished them from the other acute leukemias. Myelomonocytic leukemia could be differentiated from acute monocytic leukemia by its greater phagocytic capacity.

Alterations in lung macrophage antimicrobial activity associated with viral pneumonia

Secondary bacterial infections are a common sequelae of viral pneumonias. To study 2 functions of the phagocytic defenses of the lung, macrophages were obtained by lung lavage from parainfluenza 1 virus-infected and noninfected mice. The phagocytic capacities (binding, ingestion, and killing) of these cells were assessed in vitro against viable Candida krusei. Viral pneumonia resulted in a progressive suppression (through day 7 of the infection) of the ability of macrophages to bind candida to their surfaces by nonimmunological or complement receptors; ingestion and intracellular killing of candida were also decreased. After day 7, all these functions returned and, in fact, cells with enhanced activities were present on day 17. After introduction of virus into the lungs, the lung macrophage population increased significantly between days 3 and 7 of infection. This resulted in an increase in the phagocytic potential of the lung, despite the virus-associated suppression of the phagocytic activity in a portion of the macrophages. However, the ability of the macrophages to kill ingested microorganisms was also reduced, resulting in an overall deficiency in the lung macrophage defenses. It was concluded that viral pneumonia was associated with at least two suppressive effects on the lung macrophage-decreased receptor activity and microbicidal activity-resulting in a deficiency in the lung phagocytic defenses represented by these cells. These effects were maximal 1 week after infection and could account for the increased susceptibility of these lungs to secondary bacterial pneumonias. In contrast, during the period of convalescence, the lung macrophage antimicrobial activities were increased and reflected in enhanced resistance of the lungs to infections.

Phagocytosis and intracellular killing of pathogenic yeasts by human monocytes and neutrophils

The kinetics of phagocytosis and killing of four fungal forms with varying virulence by two types of phagocytic cells was examined. Human monocytes ingested Saccharomyces cerevisiae, Candida tropicalis, and the blastospores of Candida albicans more rapidly than did human neutrophils. There was no difference in the rate of phagocytosis of C. albicans pseudohyphae by these two cell types. Intracellular killing of each of the four fungal forms was consistently and significantly more rapid by monocytes than by neutrophils. Neutrophils were unable to destroy ingested C. albicans pseudohyphae. These experiments suggest that the monocyte plays an important role in host defenses against fungal diseases and that the relative virulence of the pathogenic yeasts in human disease may be related to the ability of these organisms to survival after being ingested by circulating phagocytes.

The differentiation of monocytes into macrophages, epithelioid cells, and multinucleated giant cells in subcutaneous granulomas. II. Peroxidatic activity

The peroxidatic (PO) activity of monocytes differentiating into macrophages, epithelioid cells, and multinucleated giant cells in subcutaneous granulomas was investigated with three different media for the demonstration of PO activity. Irrespective of the stage of differentiation, these cells did not show PO activity in the rough endoplasmic reticulum (RER) or nuclear envelope. In addition, it was found that the morphologically characteristic types of granule of the various cells of the monocyte line (the primary granules and secondary granules of monocytes, the macrophage granules, and the epithelioid cell granules), all have distinct cytochemical characteristics. Monocytes lose their primary and secondary granules during differentiation into mature macrophages. Simultaneously, the granules of both types become elongated and the secondary granule lose their halo. In contrast to monocytes, mature macrophages may contain a few microperoxisomes. During the differentiation of macrophages into epithelioid cells or multinucleated giant cells there is an increase in the number of microperoxisomes.

Human colostral cells: phagocytosis and killing of E. coli and C. albicans

Cells from human colostrum, collected from mothers within 48 hours of delivery, were examined for their capacity to phagocytose and kill Eschericia coli and Candida albicans. The phagocytic power of colostral cells was comparable to that of blood leukocytes from the same individuals. In contrast, the capacity of colostral cells to kill microorganisms was significantly less than that of blood leukocytes. Preincubation of blood leukocytes with colostrum supernatant did not reduce phagocytic indices, but reduced E. coli killing by 40% and C. albicans killing by 66%. The role of colostral cells in protecting the neonate from infection is discussed in the light of these findings.

Improvement of polymorphonuclear leucocyte oxidative and bactericidal functions in chronic granulomatous disease with 4-amino-4'-hydroxylaminodiphenyl sulphone

In an effort to restore oxidant-dependent capabilities to chronic granulomatous disease (CGD) polymorphonuclear leucocytes (PMN), we studied a dapsone derivative, 4-amino-4'-hydroxylaminodiphenyl sulphone (DDS-NOH), known to generate H2O2. After incubation of CGD PMN with 0.2 and 1.0 mM DDS-NOH for 30 min, the rate of glucose-1-14C oxidation via hexose monophosphate (HMP) shunt increased 2--4-fold and that of iodination of ingested zymosan particles 1.5--2.7-fold. Both effects could be further enhanced by superoxide dismutase (SOD) but inhibited by catalase. In three patients, 0.2 mM DDS-NOH improved in vitro killing of Staph. aureus. DDS-NOH 0.02 mM induced capping of Concanavalin A (Con A) receptor complexes suggesting interference by the drug with microtubule-associated function. Thus, optimal concentrations of DDS-NOH may be employed as an oxidant to improve metabolic and bactericidal functions of PMN from patients with CGD.

Inhibition of specific amino acid uptake in Candida albicans by lysosomal extracts from rabbit alveolar macrophages

Lysosomal-rich fractions, obtained from normal rabbit alveolar macrophages, were extracted and tested for their effects on Candida albicans. The uptake and incorporation of various compounds (amino acids, uridine, 2-deoxy-D-glucose, and Rb+) by C. albicans were measured in the presence and absence of extract. These studies demonstrated that the extract had a specific effect on the uptake of certain amino acids by C. albicans. Of the amino acids tested, the uptake of methionine valine, lysine, phenylalanine, and leucine was drastically reduced in the presence of extract, whereas proline and glutamic acid uptake was unaffected. Those amino acids whose uptake was inhibited have been shown to be transported in other yeasts by a general amino acid permease. The existence of a general amino acid permease in C. albicans is compatible with our data. Additionally, the extract had no effect on the uptake of uridine, 2-deoxy-D-glucose, and Rb+. Leakage of 86Rb by C. albicans was detected in the presence of the extract. Viability of Candida, as measured by colony-forming ability, decreased after a 16-h incubation of C. albicans with the extract.

Monocytes, macrophages, and their diseases in man

Mononuclear phagocytes are a widely distributed system of cells involved in host defense functions, immunologic reactions, disposal of unwanted organic and inorganic materials, and synthesis of biologically active compounds such as complement components and prostaglandins. The system includes early precursor cells in the bone marrow, blood monocytes, alveolar and peritoneal macrophages, sinusoidal lining cells in the spleen, and Kupffer cells in the liver. We have recently come to understand the biology of these interesting cells and the diseases they produce.