Phagocytosis Of Streptococci Research Articles

Purified Streptococcus pneumoniae Endopeptidase O (PepO) Enhances Particle Uptake by Macrophages in a Toll-Like Receptor 2- and miR-155-Dependent Manner.

Insights into the host-microbial virulence factor interaction, especially the immune signaling mechanisms, could provide novel prevention and treatment options for pneumococcal diseases. Streptococcus pneumoniae endopeptidase O (PepO) is a newly discovered and ubiquitously expressed pneumococcal virulence protein. A PepO-mutant strain showed impaired adherence to and invasion of host cells compared with the isogenic wild-type strain. It is still unknown whether PepO is involved in the host defense response to pneumococcal infection. Here, we demonstrated that PepO could enhance phagocytosis of Streptococcus pneumoniae and Staphylococcus aureus by peritoneal exudate macrophages (PEMs). Further studies showed that PepO stimulation upregulated the expression of microRNA-155 (miR-155) in PEMs in a time- and dose-dependent manner. PepO-induced enhanced phagocytosis was decreased in cells transfected with an inhibitor of miR-155, while it was increased in cells transfected with a mimic of miR-155. We also revealed that PepO-induced upregulation of miR-155 in PEMs was mediated by Toll-like receptor 2 (TLR2)-NF-κB signaling and that the increased expression of miR-155 downregulated expression of SHIP1. Taken together, these results indicate that PepO induces upregulation of miR-155 in PEMs, contributing to enhanced phagocytosis and host defense response to pneumococci and Staphylococcus aureus.

Regulation of protein phosphorylation and pathogen phagocytosis by surfactant protein A.

Surfactant protein A (SP-A), a pulmonary member of the collectin family of proteins, facilitates the rapid clearance of pathogens by upregulating immune cell functions in the lungs. SP-A binds to bacteria and targets them for rapid phagocytosis by alveolar macrophages, but the mechanism by which this stimulation occurs is not clear. To characterize the intracellular events that may be involved, we examined the roles of protein phosphorylation and cytoskeletal polymerization in SP-A-stimulated phagocytosis. In rat alveolar macrophages, SP-A stimulated rapid tyrosine phosphorylation of specific proteins in a dose- and time-dependent manner. The pattern of proteins that were phosphorylated in response to SP-A, as resolved by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was similar to that observed for immunoglobulin G (IgG)-stimulated macrophages. Both SP-A and IgG stimulated increases in phagocytosis of Streptococcus pneumoniae above levels in the absence of added protein by 394% +/- 81% and 200% +/- 25%, respectively. Phagocytosis in both cases was dependent on tyrosine kinases, protein kinase C, and actin polymerization but not on microtubule activity. These studies show that SP-A utilizes pathways similar to those used by IgG to increase macrophage phagocytosis of bacteria.

Effect of different surfactants on pulmonary group B streptococcal infection in premature rabbits

Objectives: To evaluate the effects of different surfactants on pulmonary infection with group B streptococci in premature rabbits and to examine the effects of different surfactants on pulmonary alveolar macrophage function of newborn rabbits. Model: Preterm and term rabbit pups. Methods: Rabbit pups were infected with GBS aerosols followed by intratracheal administration of either calf lung surfactant extract, minced porcine lung surfactant (Curosurf), synthetic surfactant (Exosurf Neonatal), minced bovine lung surfactant (Survanta), human amniotic fluid-derived surfactant, rabbit surfactant, saline vehicle, or no treatment. Intrapulmonary clearance of GBS was determined by comparing bacterial counts in left lungs cultured immediately after aerosol infection with similarly infected lungs analyzed 4 hours after surfactant therapy. Phagocytosis of streptococci was ascertained by microscopic examination of the right lungs fixed in situ at 4 hours. For comparison, an in vitro method was used to measure growth of GBS in the different surfactants. Results: Preterm animals had a sixfold increase in pulmonary bacterial growth compared with a slight decrease in intrapulmonary GBS in term animals when all were delivered by cesarean section ( p <0.05). In premature rabbits, GBS proliferation was lowest in animals treated with Exosurf Neonatal and highest in animals receiving Curosurf and human amniotic fluid-derived surfactant ( p <0.05). None of the surfactants promoted accelerated growth of GBS in comparison with control animals. Similar growth of GBS was seen in in vitro cultures. Intrapulmonary phagocytosis of GBS in premature pups was not altered by any of the surfactants. In term rabbit pups, the following measures of macrophage population kinetics remained normal at 1 and 24 hours after surfactant administration: viability, cell numbers based on lung lavage, and in vivo incorporation of thymidine. Conclusions: Surfactants used in clinical practice do not accelerate the in vivo growth of group B streptococci in the lungs of preterm rabbits. Some surfactants inhibit streptococcal proliferation. The effects of different surfactants are not explained by changes in macrophage function. (J P EDIATR 1994;125:939-47)

Effect of spiramycin on adhesiveness and phagocytosis of gram-positive cocci.

Three strains of Staphylococcus aureus, serotype 18, Cowan I and serotype 66438, and different species of streptococci (Streptococcus pyogenes, Str, mutans, Str. sanguis and Str. faecalis) were tested for their adherence to buccal cells (as measured by interference contrast microscopy) and phagocytosis by rat polymorphonuclear leucocytes (PMNs) (as measured by fluorescence microscopy with a vital fluorochrome, acridine orange). Pretreatment of cocci with serial two-fold dilutions of spiramycin (from 1/2 to 1/1024 the MIC), increased the diameter of bacterial cells and decreased the adherence of staphylococci and streptococci to buccal cells. Exposure of streptococci to 1/4 the MIC of spiramycin led to an increase of the phagocytic capacity of PMNs. Pretreatment of PMNs with a therapeutic concentration (2 mg/l) also stimulated the phagocytosis of streptococci. Action of spiramycin on the phagocytosis of staphylococci varied according to the strain tested. Although in-vitro results cannot be directly compared with in-vivo data, it is of interest that spiramycin decreases adherence of different Gram-positive cocci and enhances phagocytic capacity of PMNs.

Albumin bound to the surface of M protein-positive streptococci increased their phagocytosis by human polymorphonuclear leukocytes in the absence of complement and bactericidal antibodies

Using a phagocytosis assay ( Leijh 1980, Infect. Immun. 30, 421), determination of chemiluminescence, and transmission electron microscopy, the influence of the binding of albumin to M protein-positive group A streptococci on their phagocytosis by human polymorphonuclear leukocytes (PMNL) was investigated. Coating of streptococci with albumin in the absence of other serum components enhanced phagocytosis but not killing of the bacteria. Complement had no additional effect on engulfment. Fibrinogen reduced the enhancing effect of albumin. Albumin had no additional effect on the high phagocytosis rate of an M-protein-negative strain. It could be demonstrated that human PMNL bound human serum albumin-gold conjugate. The results are discussed with regard to the role of plasma proteins in the phagocytosis of streptococci under in vivo-conditions.

Infections in Sickle Cell Disease

Bacterial infections are considered a major cause of morbidity and mortality in patients, particularly children, with sickle cell disease. Infections including pneumonia, meningitis, osteomyelitis, pyelonephritis and general sepsis are more prevalent in patients with these genetic abnormalities than in normal individuals. Generally, infections are more prevalent in children than in older patients. The most common cause of severe infections in hemoglobinopathies include Diplococcus, Staphylococcus, Pneumococcus, Salmonella and Streptococcus. Several investigations have been conducted to determine the possible defects in the host defense mechanisms. Functional asplenia, defects in alternate pathway and in opsonic activity and phagocytosis of Streptococci, Staphylococci and Salmonella in sickle cell anemia patients are considered important factors predisposing these patients to bacteremia. On the other hand, a beneficial association has been demonstrated between the sickle cell gene and malaria. The hemoglobin S (Hb S) provides a natural resistance against the malarial parasite resulting in an improvement in fitness and survival over the normal (Hb AA) individuals. This communication reviews infections in sickle cell disease with a comparison of results in various populations.

Immunity to the group B streptococci: interaction of serum and macrophages with types Ia, Ib, and Ic.

The opsonization and phagocytosis of group B streptococci of types Ia, Ib, and Ic were studied in vitro by measuring the uptake of radioactivity by coverslip cultures of rabbit alevolar macrophages during incubation with radiolabeled, nonviable bacteria which had been exposed to rabbit serum. The uptake of counts per minute was quantitative, reproducible, and reversibly inhibited by cold, indicating that it was largely a measurement of phagocytic ingestion rather than of attachment of bacteria-immunoglobulin complexes to macrophage membranes. Moreover, suspended macrophages killed approximately 90% of viable streptococci in the presence of specific antiserum. The opsonic activity of immune serum was heat stable, and phagocytosis of streptococci was insignificant after incubation with normal serum and antiserum to some heterologous group B streptococci. By absorption studies, it was possible to identify the effect of antibodies to specific bacterial antigens. Phagocytosis of streptococci containing the corresponding antigens was maximal after opsonization with homologous or heterologous sera containing antibody to IaCHO, IbCHO, or Ibc protein. Phagocytosis of all three serotypes was intermediate when opsonization could be attributed to anti-IabcCHO. The opsonization of a specific group B streptococcus is complex and may involve two or more antigen-antibody systems.

PHAGOCYTOSIS IN PATIENTS AND CARRIERS OF CHRONIC GRANULOMATOUS DISEASE

The phagocytic capacity of leucocytes from four patients and two carriers of chronic granulomatous disease (C.G.D.) was compared to that of normal leucocytes. Leucocytes from C.G.D. patients phagocytised more Staphylococcus aureus than did normal leucocytes after 5, 10, and 20 minutes of incubation. Phagocytosis by leucocytes from two carriers of C.G.D. was intermediate between that in the patients and in controls. In contrast, phagocytosis of Streptococcus fœcalis, an organism readily killed by C.G.D. leucocytes, was similar for control and C.G.D. leucocytes. Enhanced phagocytosis may represent an attempt by leucocytes to compensate for a bactericidal abnormality. In addition, these observations may partly explain why carriers of C.G.D. are not more susceptible to infection despite abnormal leucocyte function. Detection of carriers using the described assay of phagocytosis appears relatively simple compared to previously described methods.

Animal Experimental Studies on Chronic Granulo-matous Inflammation and T-lymphocyte-system

The presence of lymphocytes in chronic granulomatous inflammations is frequently thought to indicate that thymus-dependent cellular immune mechanisms are involved in the pathogenesis of such processes. Therefore, in the present studies, a model of a granulomatous heaptitis (induced by heat-inactivated group A streptococci) was used to determine whether liver granulomata, consisting of macrophages and lymphocytes, could also be evoked in neonatally thymectomized or in congenitally thymus-deficient nude mice. The morphological (light and electron microscopical, immunohistological) investigations were supplemented with selective determination of T- and B-lymphocyte function. The thymus-deficient mice, after injection of streptococci, developed liver granulomata that did differ neither quanlitatively nor quantitatively from those of control animals with thymus. Lymphocytes were found within the granulomata in both animal groups. There was no evidence for functional disorder of the RES in thymus-deficient mice; on the contrary, RES-activity seemed to be increased. Phagocytosis of streptococci, their intracellular breakdown and streptococcal antigen-degradation occurred as fast or faster in such animals. PHA- and LPS-stimulation of spleen lymphocytes indicated a considerable depletion of T-cells in neonatally thymectomized mice and a complete absence of T-cells in congenitally thymus-deficient nude mice. However, radioimmunological determination of antibodies to group A streptococcal carbohydrate revealed that both groups of experimental animals possessed functionally active B-cells. Therefore, the granulomatous hepatitis described here can be defined as a focal reaction of the liver RES with "B-lymphocyte trapping". Cellular immune mechanisms are not involved in the pathogenesis of these lesions.

The Role of Complement in Immune Phagocytosis of Group A Streptococci by Mouse Peritoneal Phagocytic Cells

The role of complement in ingestion of nonencapsulated virulent group A streptococci by mouse peritoneal phagocytic cells was studied in vitro in the presence of type-specific IgG or IgM anti-M antibody. Type-specific IgG anti-M antibody significantly enhanced the phagocytosis, whereas IgM antibody was less effective in opsonization of the virulent group A streptococci. The extent of phagocytosis of streptococci sensitized with IgG or IgM anti-M antibody was not influenced by the presence of complement. These results suggested that complement was not an essential factor for efficient phagocytosis of virulent group A streptococci.

THE MECHANISM OF STREPTOCOCCUS INFECTION.

INTRODUCTION. Although a great deal of work has been done on the mechanism of streptococcus infection, both with normal and with immunized animals, many points are still left entirely in the dark. In the experiments described in this paper, an attempt is made to throw additional light on some of these points, but on account of the many inherent difficulties, the results which I have achieved by no means exhaust the problem. Shortly after the publication of his classical paper on phagocytosis in daphnia, Metchnikoff 1 made a study of phagocytosis of streptococci in the human body, in cases of erysipelas. He concluded from his observations that streptococci gain entrance through abrasions of the skin, multiply and set up an inflammation.