Reticulo-Endothelial Activity in Mice Infected with Plasmodium vinckei

SYNOPSIS. The effect of P. vinckei infections on the phagocytic activity of the reticulo-endothelial system in mice has been investigated. Changes occurring in the pattern of R.E. activity show that there is slight stimulation of phagocytosis 24 hours after the initiation of the infection at which time parasites appear in the blood. The stimulation continues and reaches a peak on the 3rd day, following which it drops to subnormal levels by the 6th and 7th days when the animals die. The parasitaemia rises abruptly from the 4th day onwards, this increase bearing a direct relationship to the fall in the level of phagocytic activity. The changes which occur during this infection are compared with those previously reported for Plasmodium gallinaceum in chicks.     

Effect of bacterial endotoxin on the phagocytic activity of the reticulo-endothelial system in rabbits of different age

Stimulation of the phagocytic activity of the reticulo-endothelial system with bacterial endotoxin was studied in newborn rabbits in the period in which they do not actively form antibodies to bacterial antigens. A markedly accelerated clearance of colloidal carbon from the blood was found in five-day-old rabbits (tested by the technique of Biozzi, Benacerraf and Halpern 1953) when relatively high doses of endotoxin were used. It is assumed that the increased resistance to infection which may be elicited in young animals in that period is due to stimulation of cellular defence mechanisms. By comparison of the stimulating effect of endotoxin on phagocytosis in five-day-old, one-month-old and adult rabbits it was found that the phagocytic cells of the R.E.S. are more susceptible to the effect of endotoxin in adults than in newborns. This difference is evident from comparisons of the phagocytic indices K and the corrected phagocytic indices α in three age groups of rabbits stimulated with different doses of endotoxin. The possible mechanism and cause of differences in sensitivity of young and adult individuals is discussed.     

A method for assessing phagocyte clearance rates in man.

By comparing the clearance rates of ICG and 99mTc-sulphur colloid from the blood stream, it has been possible to provide a method for assessing the phagocytic activity of the reticulo-endothelial system in man.     

Immunosuppression due to chronic Lantana camara, L. toxicity in sheep.

Five sheep were intoxicated with powdered L. camara, leaves at the rate of 200 mg/kg body weight daily for 110 days and another group of four sheep were drenched with distilled water daily for equal number of days which acted as control. The cell mediated immunity of intoxicated and control sheep was assessed with the help of 2,4-dinitrofluorobenzene skin sensitivity test and graft-versus-host reaction and the antibody forming potential of both the groups of animals was measured by haemagglutination against chicken red blood cells antigen. In addition, the phagocytic activity of splenic reticulo-endothelial cells was analysed by nitro blue tetrazolium test. The results indicated significant reduction of both cellular and humoral immunity due to L. camara toxicity. The non-specific phagocytic activity of splenic reticulo-endothelial cells also showed significant reduction due to L. camara, L. intoxication. The present communication constitutes the first report of in vivo immunosuppression due to chronic lantana poisoning in sheep.     

Static magnetic field as biological modifier: a study on temperature dependent influence

Magnetic fields seemingly alter a number of physiological indicators in intact animals and influence cellular metabolism. We have studied the magnetic field effects on the membrane and receptors of the reticulo-endothelial cells of bone marrow which are mainly responsible for the phagocytic activity of nanocolloid particles of human serum albumin tagged with Tc99m. A series of experiments carried out on immobilized mice exposed to a static 1.4 T SMF for 60 min at 27 degrees C or 37 degrees C body temperature showed an increased phagocytic activity at 37 degrees C and decreased activity at 27 degrees C.     

Evidence implicating the mononuclear phagocytic system of the rat in immunity to infections with Trypanosoma lewisi.

The present study emphasises the importance of the mononuclear phagocytic system of the rat in immunity to infections with Trypanosoma lewisi. Despite the great increase in the weight of the spleen, the liver played a major role in removing the parasites from the circulation. No evidence could be obtained that removal of the parasites was related to the lytic activity of specific antibody and complement.     

Cellular immune responses in chickens induced by recombinant R7 Leucocytozoon caulleryi vaccine

We have recently developed recombinant subunit vaccine consisting of second-generation schizont (2GS) membrane protein (rR7) of Leucocytozoon caulleryi. Chickens immunized with rR7 antigen acquired clear resistance to challenge by Leucocytozoon sporozoites. We examined the induction of cellular immune responses in vaccinated chickens. Spleen adherent cells from vaccinated chickens showed significantly higher phagocytic activity against 2GS-coated latex particles than did cells from adjuvant-inoculated or untreated control birds. Anti-R7 chicken IgG significantly increased the phagocytic rate of adherent cells from these 3 groups. These results show that specific cellular immune responses are induced by recombinant R7 subunit vaccine consisting of L. caulleryi 2GS protein, which suppresses the growth of parasites in the host in association with antiparasite antibodies to 2GS antigen.     

Some mechanisms involved in the prostaglandin E2 immunosuppressive effect in (CBA x C57BL)F1 mice in vivo

The cellular mechanisms involved in the immunosuppressive effect of prostaglandin E2 (PGE2) multiple injections into (CBA x C57Bl)F1 mice in vivo have been studied. PGE2 injection increases the induction of specific T-suppressors. In addition, there is a decrease in macrophage phagocytic activity and in the phagocytosis index, apparently mediated by Fc gamma receptors (Fc gamma R) and not by the macrophage complement receptor (C3R). The induction of antibody synthesis by using "immune" macrophages injected into a syngeneic recipient results in considerable decrease in the accumulation of antibody-forming cells if the macrophage donor has been pretreated with exogenous PGE2 in comparison with untreated controls. These cellular mechanisms are possibly one part of the diverse way in which PGE2 exerts an immunosuppressive effect in vivo and contributes to humoral immune response suppression.     

Lipid mediators and vector infection: Trypanosoma rangeli inhibits Rhodnius prolixus hemocyte phagocytosis by modulation of phospholipase A2 and PAF-acetylhydrolase activities

In this work we investigated the effects of Trypanosoma rangeli infection through a blood meal on the hemocyte phagocytosis in experiments using the 5th instar larvae of Rhodnius prolixus. Hemocyte phagocytic activity was strongly blocked by oral infection with the parasites. In contrast, hemocyte phagocytosis inhibition caused by T. rangeli infection was rescued by exogenous arachidonic acid (20 microg/insect) or platelet activating factor (PAF; 1 microg/insect) applied by hemocelic injection. Following the oral infection with the protozoan we observed significant attenuation of phospholipase A2 (PLA2) activities in R. prolixus hemocytes (cytosolic PLA2: cPLA2, secreted PLA2: sPLA2 and Ca+2-independent PLA2: iPLA2) and enhancement of sPLA2 activities in cell-free hemolymph. At the same time, the PAF-acetyl hydrolase (PAF-AH) activity in the cell-free hemolymph increased considerably. Our results suggest that T. rangeli infection depresses eicosanoid and insect PAF analogous (iPAF) pathways giving support to the role of PLA2 in the regulation of arachidonic acid and iPAF biosynthesis and of PAF-AH by reducing the concentration of iPAF in R. prolixus. This illustrates the ability of T. rangeli to modulate the immune responses of R. prolixus to favor its own multiplication in the hemolymph.     

Signalization and cytoskeleton activity through myosin IB during the early steps of phagocytosis in Entamoeba histolytica: a proteomic approach

Phagocytosis of human cells is a crucial activity for the virulence of the human parasite Entamoeba histolytica. This protozoan invades and destroys the intestine by killing and phagocytosing epithelial cells, erythrocytes and cells from the immune system. In this study, we used magnetic beads covered with proteins from human serum as a model system to study the early events involved in phagocytosis by E. histolytica. We validated the system showing that the beads uptake triggered the activation of the actin-myosin cytoskeleton and involved a PI3-kinase as previously described for erythrophagocytosis. We purified early phagosomes from wild-type (WT) amoeba and from parasites that overproduced myosin IB (MyoIB+), the unique unconventional myosin of E. histolytica. The MyoIB+ cells exhibit a slower and more synchronized uptake process than the WT strain. Proteomic analysis by liquid chromatography and tandem mass spectroscopy (LC-MS/MS) of the WT and MyoIB+ phagosomes allowed us to identify, for the first time, molecular actors involved in the early step of the uptake process. These include proteins involved in cytoskeleton activity, signalling, endocytosis, lytic activity and cell surface proteins. Interestingly, the proteins that we found specifically recruited on the phagosomes from the MyoIB+ strain were previously described in other eukarytotic cells, as involved in the regulation of cortical F-actin dynamics, such as alpha-actinin and formins. This proteomics approach allows a step further towards the understanding of the molecular mechanisms involved in phagocytosis in E. histolytica that revealed some interesting differences compared with phagocytosis in macrophages or Dictyostelium discoideum, and allowed to identify putative candidates for proteins linked to myosin IB activity during the phagocytic process.     

Effects of mitogens and co-mitogens on the formation of small-cell colonies in primary cultures of rat hepatocytes

Degradation of collagen by fibroblast phagocytosis is an important pathway for physiological remodelling of soft connective tissues. Perturbations of this pathway may provide a mechanism for the development of fibrotic lesions. As collagen phagocytosis may be regulated by either a change of the proportions or the activity of phagocytic cells, we quantified phagocytosis with an in vitro model system. Collagen-coated fluorescent latex beads were incubated with human gingival fibroblasts and the fluorescence associated with internalized beads was measured by flow cytometry. Cells from normal tissues that had been incubated with beads for 3 hours contained a mean of 64% phagocytic cells; however, a small subpopulation (10% of phagocytic cells) contained more than threefold higher numbers of beads per cell than the mean. In contrast, cells from fibrotic lesions exhibited a large reduction of the proportions of phagocytic cells (mean = 13.8%) and there were no cells with high numbers of beads. On the basis of ³H-Tdr labeling, cells from fibrotic lesions that had internalized beads failed to proliferate, in contrast to phagocytic cells from normal tissues, which underwent repeated cell divisions. This result was not due to variations of cell cycle phase as there was no preferential internalization of beads during different phases of the cell cycle. The low phagocytic rate of cells from fibrotic lesions was also not due to asymmetric partitioning of phagosomes at mitosis as videocinemicrography of bead-labeled phagosomes in single, pre-mitotic cells demonstrated that > 90% of phagocytic cells equally partitioned beads to daughter cells. To investigate if inhibition of phagocytosis could be replicated in vitro, cells were incubated with the fibrosis-inducing drugs nifedipine or dilantin. These cultures exhibited marked (15–75%), dose-dependent reductions in the proportions of phagocytic cells, but there was no reduction in bead number per cell. Fibrotic lesions appear to contain fibroblasts with marked deficiencies in phagocytosis and the reduced phagocytic activity of these cells may contribute to unbalanced degradation and fibrosis. © 1993 Wiley-Liss, Inc.     

Radiation effects on rat testes. V. Studies on lysosomal enzymes (acid phosphatase and acid DNAse) and their physiological significance following partial body gamma-irradiation.

Acid phosphatase is present in the nucleus and cytoplasm of cells in the seminiferous tubules and the interstitium of rat testes. The effect of irradiation on acid phosphatase is dependent on the environmental temperature and the dose of irradiation. It appears that initial rise in the enzyme at a low radiation dose and a high environmental temperature or at a high dose and low temperature is associated with a lysosomal breakdown of the germinal cells of the testes. A decrease in acid phosphatase in the advanced stages of radiation injury is a secondary radiation effect which may lead to decreased metabolic synthesis of phosphate esters owing to the unavailability of orthophosphate in the testicular tubules. The reduced acid phosphatase activity can be detected in the seminiferous tubules, suggesting that the enzyme activity is related to the state of the germ cell population. An initial increase in acid phosphatase is matched by an initial rise in acid DNAse within hours of irradiation, further suggesting that there is radiation interaction with the cells of the germinal epithelium. The enhanced activity of DNAse following a 2nd week of irradiation at 2000 R confirms the phagocytic activity of the non-germinal cells.     

Reticuloendothelial function in renal allograft recipients.

The phagocytic capacity of the reticuloendothelial system (R.E.S.) was assessed in patients with chronic renal failure and in renal transplant recipients. R.E.S. phagocytosis was increased in the former group. Soon after transplantation R.E.S. phagocytosis was moderately reduced (through levels were comparable with those of normal controls) but was particularly reduced after high-dose corticosteroid treatment for rejection. In long-term allograft recipients R.E.S. phagocytosis was also depressed though steroid maintenance doses were small.     

Ingestion and digestion of erythocytes by non-irradiated and irradiated macrophages.

The effect of X-rays (1300 R) and gamma irradiation (3000 R) on phagocytic activity of mouse peritoneal macrophages cultivated in vitro was studied using human glutaraldehyde-fixed red blood cells. The peroxidative activity of haemoglobin was cytochemically detected by the DAB method. The obtained results indicate that the applied dose of X-irradiation does not affect the phagocytic activity of macrophages. On the contrary, the gamma irradiation (3000 R) causes acceleration of phagocytic activity of macrophages with concomitant impairment of intracellular digestion of ingested material. Weakened cytochemical reaction for acid phosphatase suggests that sufficiently high doses of irradiation cause some disturbances in the biosynthesis of lysosomal enzymes in exposed macrophages.     

Phagocytosis of Plasmodium chabaudi: modulation by immune serum and antigen in vitro

The phagocytosis of free Plasmodium chabaudi parasite by resident peritoneal macrophages of mouse was studied in an in vitro system. The effect of antimalarial antiserum (HIS) was assessed by preincubation of parasite macrophages and both parasite and macrophages with HIS prior to use in phagocytic assays. Highest phagocytic index was obtained with HIS pretreated parasites. The two activities viz. opsonic (parasite dependent) and cytophilic (macrophage dependent) were noted to operate independent of each other. The phagocytosis promoting activity was found to be complement dependent. The receptor site for binding of HIS opsonized but not medium opsonized parasite on the surface of macrophages was blocked by pretreatment of these cells with HIS-soluble antigen combination.     

Living off a fish: a trade-off between parasites and the immune system

Research in fish immune system and parasite invasion mechanisms has advanced the knowledge of the mechanisms whereby parasites evade or cope with fish immune response. The main mechanisms of immune evasion employed by fish parasites are reviewed and considered under ten headings. 1) Parasite isolation: parasites develop in immuno-privileged host tissues, such as brain, gonads, or eyes, where host barriers prevent or limit the immune response. 2) Host isolation: the host cellular immune response isolates and encapsulates the parasites in a dormant stage without killing them. 3) Intracellular disguise: typical of intracellular microsporidians, coccidians and some myxosporeans. 4) Parasite migration, behavioural and environmental strategies: parasites migrate to host sites the immune response has not yet reached or where it is not strong enough to kill them, or they accommodate their life cycles to the season or the age in which the host immune system is down-regulated. 5) Antigen-based strategies such as mimicry or masking, variation and sharing of parasite antigens. 6) Anti-immune mechanisms: these allow parasites to resist innate humoral factors, to neutralize host antibodies or to scavenge reactive oxygen species within macrophages. 7) Immunodepression: parasites either suppress the fish immune systems by reducing the proliferative capacity of lymphocytes or the phagocytic activity of macrophages, or they induce apoptosis of host leucocytes. 8) Immunomodulation: parasites secrete or excrete substances which modulate the secretion of host immune factors, such as cytokines, to their own benefit. 9) Fast development: parasites proliferate faster than the ability of the host to mount a defence response. 10) Exploitation of the host immune reaction. Knowledge of the evasion strategies adopted by parasites will help us to understand host-parasite interactions and may therefore help in the discovery of novel immunotherapeutic agents or targeted vaccines, and permit the selection of host-resistant strains.     

Myosin II-dependent exclusion of CD45 from the site of Fcγ receptor activation during phagocytosis

Fcγ receptor (FcγR)-mediated phagocytosis requires myosin II activity. Here we show that myosin II contributes to FcγR activation and subsequent F-actin assembly at the nascent phagocytic cup. Inhibition of myosin II attenuates phosphorylation of the immunoreceptor tyrosine-based activation motif (ITAM) of FcγR and binding of Syk to the ITAM. Furthermore, FcγR clusters independently of myosin II activity at the phagocytic cup, from which the receptor-like protein tyrosine phosphatase CD45 is excluded depending on myosin II activity. These findings suggest that myosin II-dependent segregation of CD45 from FcγR facilitates phosphorylation of the ITAM and triggers phagocytosis.     

The Mannose Receptor (CD206) is an important pattern recognition receptor (PRR) in the detection of the infective stage of the helminth Schistosoma mansoni and modulates IFNγ production

In this study, infective larvae of the parasitic helminth Schistosoma mansoni were shown to contain a large number of glycosylated components specific for the Mannose Receptor (MR; CD206), which is an important pattern recognition receptor (PRR) of the innate immune system. MR ligands were particularly rich in excretory/secretory (E/S) material released during transformation of cercariae into schistosomula, a process critical for infection of the host. E/S material from carboxyfluorescein diacetate succinimidyl ester (CFDA-SE)-labelled cercariae showed enhanced binding by cells lines that over-express the MR. Conversely, uptake was significantly lower by bone marrow-derived macrophages (MΦ) from MR(-/-) mice, although they were more active as judged by enhanced pro-inflammatory cytokine production and CD40 expression. After natural percutaneous infection of MR(-/-) mice with CFDA-SE-labelled parasites, there were fewer cells in the skin and draining lymph nodes that were CFDA-SE(+) compared with wild-type mice, implying reduced uptake and presentation of larval parasite antigen. However, antigen-specific proliferation of skin draining lymph node cells was significantly enhanced and they secreted markedly elevated levels of IFNγ but decreased levels of IL-4. In conclusion, we show that the MR on mononuclear phagocytic cells, which are plentiful in the skin, plays a significant role in internalising E/S material released by the invasive stages of the parasite which in turn modulates their production of pro-inflammatory cytokines. In the absence of the MR, antigen-specific CD4(+) cells are Th1 biased, suggesting that ligation of the MR by glycosylated E/S material released by schistosome larvae modulates the production of CD4(+) cell specific IFNγ.     

Simultaneous flow cytometric assessment for cellular types and phagocytic abilities of the haemocytes of the hard clam, Meretrix lusoria

The aim of this study was to devise a simple protocol for flow cytometric analysis to separate various haemocytic populations of the hard clam Meretrix lusoria based on the mitochondrial membrane potential diversity detected by the fluorescence probe 3,3-dihexyloxacarbocyanine iodide (DiOC6). Compared with the traditional technique for separation of haemocytic populations, continuous Percoll gradient centrifugation, our novel method was more efficient and yielded a higher ratio in separating the clams' haemocytic populations. Based on fluorescence 1 (FL-1) and side scatter (SSC) analysis for haemocytes stained with various fluorescent densities of DiOC6 using flow cytometer, the data showed that there were three obvious cell regions R1, R2, and R3, identified by hyalinocytes, small granulocytes and large granulocytes, respectively. At the same time our results showed that the percentages of haemocytes in R1, R2, and R3 were 49.71+/-0.65%, 19.35+/-00.74%, 30.94+/-0.69%, respectively. After classifying the haemocytic populations, phagocytic activity of the haemocytes was simultaneously analysed with phycoerythrin (PE)-labeled Vibrio vulnificus and detected by flow cytometry. Our results demonstrated that there were higher percentages of large granulocytes compared with hyalinocytes and the percentage of small granulocytes was related to the mitochondrial membrane potential and phagocytic activities.