Presence Of Phagocytes Research Articles

Stimulating the autophagic-lysosomal axis enhances host defense against fungal infection in a zebrafish model of invasive Aspergillosis

ABSTRACT The increasing prevalence of antifungal-resistant human pathogenic fungi, particularly azole-resistant Aspergillus fumigatus, is a life-threatening challenge to the immunocompromised population. Autophagy-related processes such as LC3-associated phagocytosis have been shown to be activated in the host response against fungal infection, but their overall effect on host resistance remains uncertain. To analyze the relevance of these processes in vivo, we used a zebrafish animal model of invasive Aspergillosis. To confirm the validity of this model to test potential treatments for this disease, we confirmed that immunosuppressive treatments or neutropenia rendered zebrafish embryos more susceptible to A. fumigatus. We used GFP-Lc3 transgenic zebrafish to visualize the autophagy-related processes in innate immune phagocytes shortly after phagocytosis of A. fumigatus conidia, and found that both wild-type and melanin-deficient conidia elicited Lc3 recruitment. In macrophages, we observed GFP-Lc3 accumulation in puncta after phagocytosis, as well as short, rapid events of GFP-Lc3 decoration of single and multiple conidia-containing vesicles, while neutrophils covered single conidia-containing vesicles with bright and long-lasting GFP-Lc3 signal. Next, using genetic and pharmacological stimulation of three independent autophagy-inducing pathways, we showed that the antifungal autophagy response improves the host survival against A. fumigatus infection, but only in the presence of phagocytes. Therefore, we provide proof-of-concept that stimulating the (auto)phagolysosomal pathways is a promising approach to develop host-directed therapies against invasive Aspergillosis, and should be explored further either as adjunctive or stand-alone therapy for drug-resistant Aspergillus infections.

Protection of Insects against Viral Infection by Apoptosis-Dependent Phagocytosis.

We investigated whether phagocytosis participates in the protection of insects from viral infection using the natural host-virus interaction between Drosophila melanogaster and Drosophila C virus (DCV). Drosophila S2 cells were induced to undergo apoptotic cell death upon DCV infection. However, UV-inactivated virus was unable to cause apoptosis, indicating the need for productive infection for apoptosis induction. S2 cells became susceptible to phagocytosis by hemocyte-derived l(2)mbn cells after viral infection, and the presence of phagocytes in S2 cell cultures reduced viral proliferation. Phagocytosis depended, in part, on caspase activity in S2 cells, as well as the engulfment receptors Draper and integrin βν in phagocytes. To validate the in vivo situation, adult flies were abdominally infected with DCV, followed by the analysis of fly death and viral growth. DCV infection killed flies in a dose-responding manner, and the activation of effector caspases was evident, as revealed by the cleavage of a target protein ectopically expressed in flies. Furthermore, hemocytes isolated from infected flies contained DCV-infected cells, and preinjection of latex beads to inhibit the phagocytic activity of hemocytes accelerated fly death after viral infection. Likewise, viral virulence was exaggerated in flies lacking the engulfment receptors, and was accompanied by the augmented proliferation of virus. Finally, phagocytosis of DCV-infected cells in vitro was inhibited by phosphatidylserine-containing liposome, and virus-infected flies died early when a phosphatidylserine-binding protein was ectopically expressed. Collectively, our study demonstrates that the apoptosis-dependent, phosphatidylserine-mediated phagocytosis of virus-infected cells plays an important role in innate immune responses against viral infection in Drosophila.

Evolution of Innate Immunity: Clues from Invertebrates via Fish to Mammals.

Host responses against invading pathogens are basic physiological reactions of all living organisms. Since the appearance of the first eukaryotic cells, a series of defense mechanisms have evolved in order to secure cellular integrity, homeostasis, and survival of the host. Invertebrates, ranging from protozoans to metazoans, possess cellular receptors, which bind to foreign elements and differentiate self from non-self. This ability is in multicellular animals associated with presence of phagocytes, bearing different names (amebocytes, hemocytes, coelomocytes) in various groups including animal sponges, worms, cnidarians, mollusks, crustaceans, chelicerates, insects, and echinoderms (sea stars and urchins). Basically, these cells have a macrophage-like appearance and function and the repair and/or fight functions associated with these cells are prominent even at the earliest evolutionary stage. The cells possess pathogen recognition receptors recognizing pathogen-associated molecular patterns, which are well-conserved molecular structures expressed by various pathogens (virus, bacteria, fungi, protozoans, helminths). Scavenger receptors, Toll-like receptors, and Nod-like receptors (NLRs) are prominent representatives within this group of host receptors. Following receptor–ligand binding, signal transduction initiates a complex cascade of cellular reactions, which lead to production of one or more of a wide array of effector molecules. Cytokines take part in this orchestration of responses even in lower invertebrates, which eventually may result in elimination or inactivation of the intruder. Important innate effector molecules are oxygen and nitrogen species, antimicrobial peptides, lectins, fibrinogen-related peptides, leucine rich repeats (LRRs), pentraxins, and complement-related proteins. Echinoderms represent the most developed invertebrates and the bridge leading to the primitive chordates, cephalochordates, and urochordates, in which many autologous genes and functions from their ancestors can be found. They exhibit numerous variants of innate recognition and effector molecules, which allow fast and innate responses toward diverse pathogens despite lack of adaptive responses. The primitive vertebrates (agnathans also termed jawless fish) were the first to supplement innate responses with adaptive elements. Thus hagfish and lampreys use LRRs as variable lymphocyte receptors, whereas higher vertebrates [cartilaginous and bony fishes (jawed fish), amphibians, reptiles, birds, and mammals] developed the major histocompatibility complex, T-cell receptors, and B-cell receptors (immunoglobulins) as additional adaptive weaponry to assist innate responses. Extensive cytokine networks are recognized in fish, but related signal molecules can be traced among invertebrates. The high specificity, antibody maturation, immunological memory, and secondary responses of adaptive immunity were so successful that it allowed higher vertebrates to reduce the number of variants of the innate molecules originating from both invertebrates and lower vertebrates. Nonetheless, vertebrates combine the two arms in an intricate inter-dependent network. Organisms at all developmental stages have, in order to survive, applied available genes and functions of which some may have been lost or may have changed function through evolution. The molecular mechanisms involved in evolution of immune molecules, might apart from simple base substitutions be as diverse as gene duplication, deletions, alternative splicing, gene recombination, domain shuffling, retrotransposition, and gene conversion. Further, variable regulation of gene expression may have played a role.

A privileged intraphagocyte niche is responsible for disseminated infection ofStaphylococcus aureusin a zebrafish model

The innate immune system is the primary defence against the versatile pathogen, Staphylococcus aureus. How this organism is able to avoid immune killing and cause infections is poorly understood. Using an established larval zebrafish infection model, we have shown that overwhelming infection is due to subversion of phagocytes by staphylococci, allowing bacteria to evade killing and found foci of disease. Larval zebrafish coinfected with two S. aureus strains carrying different fluorescent reporter gene fusions (but otherwise isogenic) had bacterial lesions, at the time of host death, containing predominantly one strain. Quantitative data using two marked strains revealed that the strain ratios, during overwhelming infection, were often skewed towards the extremes, with one strain predominating. Infection with passaged bacterial clones revealed the phenomenon not to bedue to adventitious mutations acquired by the pathogen. After infection of the host, all bacteria are internalized by phagocytes and the skewing of population ratios is absolutely dependent on the presence of phagocytes. Mathematical modelling of pathogen population dynamics revealed the data patterns are consistent with the hypothesis that a small number of infected phagocytes serve as an intracellular reservoir for S. aureus, which upon release leads to disseminated infection. Strategies to specifically alter neutrophil/macrophage numbers were used to map the potential subpopulation of phagocytes acting as a pathogen reservoir, revealing neutrophils as the likely ‘niche’. Subsequently in a murine sepsis model, S. aureus abscesses in kidneys were also found to be predominantly clonal, therefore likely founded by an individual cell, suggesting a potential mechanism analogous to the zebrafish model with few protected niches. These findings add credence to the argument that S. aureus control regimes should recognize both the intracellular as well as extracellular facets of the S. aureus life cycle.

Semen analysis by electron and fluorescence microscopy in a case of partial hydatidiform mole reveals a high incidence of abnormal morphology, diploidy, and tetraploidy

To perform a highly detailed semen analysis in a man whose wife had a partial mole. Case report. Gynecology departments of two university hospitals and a laboratory of histology/embryology. A 32-year-old man whose wife had a partial mole. Sperm characteristics were examined by light microscopy, morphology was analysed by electron microscopy (TEM), DNA fragmentation was evaluated by TUNEL using fluorescence microscopy, and chromosomal abnormalities were assessed by fluorescence in situ hybridization using probes for chromosomes 13, 15, 16, 18, 21, 22, X, and Y. Sperm count, motility, morphology, DNA fragmentation, and incidence of diploidy, tetraploidy, and aneuploidy. Sperm concentration was 61 million/mL, with 31% progressive motility and 4% normal morphology. TEM revealed a high incidence of head, neck, and tail abnormalities as well as the presence of phagocytes. DNA fragmentation was within normal limits (11.6%). Aneuploidy levels were low for all chromosomes tested. However, there was a high level of diploidy, with XY, XX, and YY constitution. Tetraploid sperm (XXYY) were also noted. Semen analysis revealed a high incidence of abnormal morphology and increased diploidy. It may be important to perform FISH testing, to verify increased diploidy in sperm, in men whose wives have had partial moles. These couples could be informed of the option to have preimplantation genetic diagnosis as a means to distinguish between diploid and triploid embryos arising from fertilization of a haploid egg by diploid sperm.

Bacteria--phagocyte dynamics, axiomatic modelling and mass-action kinetics

Axiomatic modeling is ensued to provide a family of models that describe bacterial growth in the presence of phagocytes, or, more generally, prey dynamics in a large spatially homogenous eco-system. A classification of the possible bifurcation diagrams that arise in such models is presented. It is shown that other commonly used models that do not belong to this class may miss important features that are associated with the limited growth curve of the bacteria (prey) and the saturation associated with the phagocytosis (predator kill) term. Notably, these features appear at relatively low concentrations, much below the saturation range. Finally, combining this model with a model of neutrophil dynamics in the blood after chemotherapy treatments we obtain new insights regarding the development of infections under neutropenic conditions.

The Influence of Pre‐ and Post‐ovulatory Insemination and Early Pregnancy on the Infiltration by Cells of the Immune System in the Sow Oviduct

The aim of this study was to investigate the influence of pre- and post-ovulatory insemination and early pregnancy on the distribution of immune cells in the oviduct. Eighteen sows were pre-ovulatory and sixteen sows were post-ovulatory inseminated and slaughtered at different times, 5-6 h after insemination, 20-25 h and approximately 70 h after ovulation, day 11 and day 19. Immediately after slaughter, oviductal samples of three different segments (isthmus, ampulla and infundibulum) were fixed, embedded in plastic resin and stained with toluidine blue or cryofixed and stored in a freezer at -70 degrees C until analysed by immunohistochemistry (pre-ovulatory inseminated sows) with an avidin-biotin peroxidase method. Quantitative and qualitative examinations of oviductal epithelium and subepithelial connective tissue were performed by light microscopy. After pre- or post-ovulatory insemination, neutrophils were not observed in the oviductal epithelium from any of the segments or groups. The numbers of intraepithelial lymphocytes of all sows as well as CD2- and CD3-positive cells of the pre-ovulatory inseminated sows were higher in the infundibulum than in the other segments (p < or = 0.001). In the subepithelial connective tissue of the pre-ovulatory inseminated sows, significantly higher numbers of lymphocytes (p < or = 0.001) and plasma cells (p < or = 0.001) were found in infundibulum than in isthmus. Neutrophils were found mainly in infundibulum, the number approximately 40 h after pre-ovulatory insemination was significantly higher (p < or = 0.05) than in the other groups and segments. Significantly higher numbers of CD2 than CD3-positive cells were found for all groups and segments. In the subepithelial connective tissue of post-ovulatory inseminated sows, the numbers of lymphocytes was higher (p < or = 0.001) at day 19 than up to 50 h after insemination and lower (p < or = 0.001) in isthmus than in ampulla and infundibulum. Neutrophils were found in infundibulum in almost all groups and the number was significantly higher (p < or = 0.05) in the infundibulum up to 50 h after insemination than in other segments. In the oviductal epithelium, no influence of insemination was found on the presence of phagocytes, i.e. neutrophils and macrophages, but on lymphocytes. In the infundibular connective tissue, pre-ovulatory insemination had an effect on neutrophil distribution, indicating an active immune response to insemination in the upper segment. Post-ovulatory insemination changed the oviductal immune cell pattern.

Altered Self-Erythrocyte Recognition and Destruction in an Inbred Line of Tilapia (Oreochromis aureus)

Carboxyfluorescein diacetate (cFDA)-stained autologous and syngeneic tilapia (Oreochromis aureus) erythrocytes are recognized by effector peripheral blood leukocytes and lysed after a short culture period of 4 h. The hemolysis level was evaluated by measuring the fluorescence of the released cFDA. The degree of lysis of stained target erythrocytes of 60 individuals revealed a trimodal distribution statistically stratified into three groups of low (LR), intermediate (IR), and high (HR) responders. Depletion of the majority of phagocytes from leukocytes lowered the lysis level of HR to that of LR. A highly significant increase of LR cytotoxicity was obtained after the addition of conditioned medium from HR but only in the presence of phagocytes. Genetic analysis of offspring from four crosses (IR x HR, IR x LR, HR x LR, and LR x LR) revealed a quantitative trait locus (QTL) segregating for the level of response linked to markers UNH207 and UNH231 on linkage group 6 of tilapia. Based on segregation analysis of 58 gynogenetic BIU-1 offspring, the distances from the centromere were estimated as 21.5, 11.5, and 9.0 cM for UNH207, UNH231, and the QTL, respectively. It is suggested that 1) self-target recognition and destruction requires both cFDA-altered self-erythrocyte membrane and membrane structures normally present in autologous, syngeneic, and xenogeneic targets; 2) natural cytotoxic cells and/or macrophages are involved in erythrocyte lysis; and 3) the lysis level is codominantly inherited by a QTL segregating on tilapia linkage group 6.

UV-B irradiated cell lines execute programmed cell death in various forms.

We investigated changes typical for apoptosis in various cell lines after UV-B irradiation. Using established methods for detection of apoptosis we demonstrate changes of cellular morphology, phosphatidylserine (PS) exposure, ollgonucleosomal DNA fragmentation and generation of hypochrome nuclei. To isolated high-molecular-weight (hmwt) DNA fragments we engaged a new method avoiding pulse field gel electrophoresis. Most UV-B irradiated cell lines showed oligonucleosomal DNA fragmentation, hypochrome nuclei, morphological changes, annexin-V binding and positive TUNEL reaction. However, no oligonucleosomal DNA fragmentation could be detected in Raji and HaCaT cells. Whereas HaCaT cells displayed all other changes typical for apoptosis, Raji cells were TUNEL negative, formed low amounts of hmwt DNA and showed an 'atypically' low hypochrome shift. Nevertheless, UV-B irradiated Raji cells excluded propidium iodide (PI), bound annexin-V and stopped proliferation. This suggests that Raji cells underwent growth arrest with exposure of PS being the only feature of apoptosis. However, in the presence of phagocytes expressing the phosphatidylserine receptor these cells would share the removal pathway with apoptotic cells. Since UV-B induced programmed cell death differs in dependence of cells under investigation, the failure to detect oligonucleosomal DNA fragmentation or chromatin condensation is not suitable to exclude programmed (apoptotic?) cell death.

Role of Helicobacter pylori surface structures in bacterial interaction with macrophages.

Helicobacter pylori infection is associated with a marked infiltration of the gastric epithelium by neutrophils, macrophages, lymphocytes, and plasma cells. Despite the presence of phagocytes in close vicinty to H pylori microbes a great number of people are unable to eradicate bacteria. To investigate the involvement of multiple bacterial 'adhesins' and some phagocytic receptors in the process of the ingestion of H pylori by macrophages. BACTERIA: H pylori strains differing in the expression of sialic acid dependent (sHA) or sialic acid independent (HA) haemagglutinin and heparan sulphate binding were selected for the study. The uptake of fluorescein labelled H pylori bacteria by a homogenous macrophage cell line J 774A.1 was estimated in a quantitative fluorometric assay. The ingestion of H pylori 17874 and 25 strains expressing sHA was inhibited by the pretreatment of the bacteria with anti-sHA antibodies or fetuin as well as by treatment of the macrophages with neuraminidase. In contrast the uptake of H pylori 17875 strain expressing HA remained unchanged. The phagocytosis of all investigated bacteria was inhibited after the treatment with heparin, hyaluronic acid or vitronectin with fresh but not heat inactivated serum. The results suggest that H pylori surface compounds binding host proteins such as fetuin, heparin/haparan sulphate, hyaluronic acid, and vitronectin in the presence of complement, could allow the bacteria to avoid phagocytosis.

Seminal Phagocytes Detection at Light-Microscopy Level using Three Different Techniques

The phagocytes are normally present in the conective tissue at different organs, and their number increased in immunological or inflammatory processes. In these cases, they are present too in corporal fluids.The presence of phagocytes in semen was referred by several authors, but that phenomenon has not been suficiently analysed. At smear Papanicolaou stained analysis, the seminal phagocytes can be inadverted thus, their relationship to the male infertility or another reproductive tract pathology can not be established.In this study we implemented three techniques to detect the presence of phagocytes in semen of 28 infertile patients: Myeloperoxidase for polymorphonuclears (leukocyte), Neutral red for macrophages and the semithin sections analysis at light microscopical level of the seminal pellet obtained by centrifugation and included in epoxyresin.

Wound Repair in the Amphioxus ( Branchiostoma platae), an Animal Deprived of Inflammatory Phagocytes

The existence of phagocytes in the Amphioxus is a matter of debate since early studies of Metchnikoff, who could not induce inflammation in this animal. To reinvestigate this important phenomenon, we sectioned the distal portion of the animal and analyzed, by morphological methods, the presence of phagocytes in the wound. The analysis of the wound by optical and electron microscopy did not detect cells with morphological characteristics of phagocytes in it. The wound is completely covered by the external cuticle of the animal 24 hr after the lesion was made. A second section of the animal leads to abnormal healing of the lesion. The insertion of a surgical silk thread in the muscle of the animals results—after 13 days—in a collection of cells surrounding the foreign body. The ultrastructural analysis of these cells showed they are endothelial cells rather than specialized phagocytes. Yet, the Amphioxus is able to mount an allograph rejection when the animals are tied together by suture. This intriguing capacity of the Amphioxus to cope with tissue healing, infection, and other pathologies without phagocytes is discussed.

Studies on thermophile products. VI. Activation of mouse peritoneal macrophages by bis(2-hydroxyethyl) trisulfide.

The biological effects of a cytotoxic substance (BS-1), isolated from Bacillus stearothermophilus UK563 and identified as bis(2-hydroxyethyl) trisulfide, on elicited mouse peritoneal macrophages induced by a casein injection, were investigated in vitro. BALB/c mouse macrophages treated or pretreated with BS-1 (1-10 micrograms/ml) showed cytotoxicity against syngeneic DBA/2 mouse P815 mastocytoma. BS-1 also showed weak cytotoxicity directly against P815 in the absence of macrophages. BS-1 significantly increased the glucose consumption of macrophages without producing cytotoxicity. This trisulfide compound increased nitric oxide formation, interleukin-1 production and prostaglandin E2 release in macrophages. It did not, however, increase the production of active oxygen species in macrophages, but it reduced cytochrome c in the presence of phagocytes. These results indicate that BS-1 activates macrophages to the cytolytic stage.

Increased oxidative metabolism in PMA-activated lymphocytes: a flow cytometric study.

Flow cytometry and the fluorescent dyes DCF and R123 were used to examine oxygen metabolite production in human leukocytes and T-lymphoblastoid Jurkat cells, activated by PMA or by FMLP. When unseparated leukocytes were activated by PMA, oxidative products were generated not only in PMN and monocytes but also to a lower extent in lymphocytes. These responses were correlated with protein kinase C activation. PMA did not, however, induce the synthesis of reactive oxygen species in isolated lymphocytes. FMLP did not affect lymphocyte oxidative metabolism when added to the whole leukocyte mixture, but activated only the phagocyte populations. Similarly, Jurkat cells which alone were unresponsive to PMA, became strongly fluorescent when they were mixed with PMN and treated with this activator. In all cases, they did not respond to FMLP. Superoxide dismutase and catalase addition did not prevent the lymphoid cell response in the presence of phagocytes, whereas Desferal did. These data indicate that under physiological conditions, activated lymphocytes are capable of oxidative metabolism and also evidence some close relation between the leukocyte populations. We discuss the putative mechanism of oxygen metabolite generation in lymphocytes and the role of these metabolites in the immune response.

Lectin activity and a protease inhibitor in mucus from the skin of Branchiostoma lanceolatum

The existence of phagocytes in the Amphioxus is a matter of debate since early studies of Metchnikoff, who could not induce inflammation in this animal. To reinvestigate this important phenomenon, we sectioned the distal portion of the animal and analyzed, by morphological methods, the presence of phagocytes in the wound. The analysis of the wound by optical and electron microscopy did not detect cells with morphological characteristics of phagocytes in it. The wound is completely covered by the external cuticle of the animal 24 hr after the lesion was made. A second section of the animal leads to abnormal healing of the lesion. The insertion of a surgical silk thread in the muscle of the animals results—after 13 days—in a collection of cells surrounding the foreign body. The ultrastructural analysis of these cells showed they are endothelial cells rather than specialized phagocytes. Yet, the Amphioxus is able to mount an allograph rejection when the animals are tied together by suture. This intriguing capacity of the Amphioxus to cope with tissue healing, infection, and other pathologies without phagocytes is discussed.

Phagocytosis of Campylobacter jejuni and its intracellular survival in mononuclear phagocytes.

In vitro phagocytosis and intracellular survival of Campylobacter jejuni strain 2964 in mononuclear phagocytes were studied. The following three types of mononuclear phagocytes were used: a J774G8 peritoneal macrophage line derived from BALB/c mice, resident BALB/c peritoneal macrophages, and human peripheral blood monocytes. When C. jejuni and mononuclear phagocytes were combined at a ratio of 75:1, light microscopy, fluorescent microscopy, and electron microscopy all indicated that C. jejuni cells were readily phagocytized. The majority of C. jejuni cells were spirals immediately following ingestion and were rapidly converted to the coccal form within 4 to 8 h. Conversion from the spiral form to the coccal form was complete in the presence of phagocytes within 96 h. In control preparations without phagocytes, conversion began after 24 h and was complete after 48 h. The extent of phagocytosis over time was determined by observing Giemsa-stained preparations and counting the number of intracellular bacterial colony-forming units after removal of extracellular C. jejuni. Human monocytes ingested C. jejuni more rapidly and vigorously than murine macrophages. Intracellular survival of C. jejuni was examined by measuring the number of C. jejuni colony-forming units associated with phagocytes after phagocytosis for 2 h and removal of extracellular bacteria. C. jejuni survived intracellularly for up to 6 to 7 days.

Biochemical studies on rabbits with aluminium induced neurofilament accumulations.

The activities of acid phosphatase, hexosaminidase, beta-galactosidase, Mg2+-stimulated Na+K+ATPase, fumarase and ATP:citrate lyase were measured in grey matter of rabbit spinal cord 7-8 days after intra-ventricular or intra-cisternal injection of aluminium. RNA, DNA, and water content were measured in whole spinal cords. Choline acetyltransferase (CAT) and acetylcholinesterase were assayed in dorsal grey matter of the cord, which contained no aluminium-induced neurofilament accumulations (NFAs), and ventral grey matter, which had large numbers of such NFAs. CAT was also assayed in the hypoglossal nerve. None of these measures were consistently altered in the aluminium treated rabbits, although the activity of beta-galactosidase was increased in the NFA-free caudate nucleus of rabbits given aluminium intra-ventricularly, possibly due to the presence of phagocytes on the ventricular surface of the caudate. It is concluded that neither aluminium nor its induced NFAs has a gross effect on neuronal metabolism within 7-8 days.

Lipoteichoic acid inhibition of phagocytosis of Staphylococcus aureus by human polymorphonuclear leukocytes

Under the influence of cell wall antibiotics, tolerant strains of Staphylococcus aureus have been shown to excrete increased amounts of lipoteichoic acid (LTA) into the growth medium, relative to nontolerant strains. The effect of LTA on the phagocytic and bactericidal rate of isolated neutrophils for S. aureus was studied to determine if the enhanced production of LTA by tolerant strains might account in part for the increased severity of infections due to tolerant organisms. Phagocytosis was measured as leukocyte-associated radioactivity after incubation of neutrophils, human serum, and radiolabeled S. aureus in microtiter wells. The addition of LTA, at final concentrations ranging from 0–5 nmol/ml, to the incubation mixtures resulted in a dose-dependent inhibition of phagocytosis. The decreased uptake of S. aureus by the neutrophils was accompanied by an increase in the number of organisms surviving in the presence of phagocytes. Such an inhibition was not observed when preopsonized bacteria were employed. These results suggest that LTA is able to interfere with the normal rapid opsonization of S. aureus in in vitro phagocytic systems.

Host-parasite relationships in experimental Streptobacillus moniliformis arthritis in mice.

Several variables of host and parasite, relating to the establishment of the chronic Streptobacillus moniliformis-induced arthritis, were studied. Results from these studies indicated (i) that intravenous inoculation of the organism produced a progressive bacteremia and a polyarthritis, whereas subcutaneous inoculation into the top of the back foot produced an intermittent bacteremia and arthritis only in that foot, (ii) that serum-broth-grown cells were more virulent than serum-agar-grown cells, (iii) that young animals were more susceptible to infection than old, and (iv) that the organism apparently had a predilection for joints. It was also determined that the leukocyte and antibody responses of mice to infection were minimal with a slight neutrophilia and a maximum antibody titer of 1:640 detected after infection. Measurements of the effectiveness of antibody and leukocytes in prevention or resolution of infection indicated (i) that the presence of homologous antibody prior to infection prolonged the incubation period for development of the lesion, (ii) that the opsonic index was 1.2 to 1.4, and (iii) that the organism was apparently resistant to destruction by in vitro phagocytosis and actually increased in number in the presence of phagocytes. It was concluded that these represented some of the prime factors contributing to the establishment of the infection and its chronicity.

Effect of centrifugation on the immune reaction of rabbit blood lymphocytes following antigen stimulation in vitro.

An increase in the immune reaction towards sheep red cells (SRC) was observed in SRC‐stimulated cultures containing leucocytes from SRC‐immunized rabbits when the leucocyte‐SRC suspensions were centrifuged at high speed before incubation. Immune reaction was also evident in a majority of culture tubes containing purified lymphocytes stimulated with SRC and centrifuged at high speed, while no response was observed in non‐centrifuged tubes. The findings indicate that SRC antigen may stimulate lymphocytes directly without the presence of phagocytes if a close contact is obtained between antigen and reacting cells.