Immunoregulation in experimental filariasis. III. Demonstration and characterization of antigen-specific suppressor cells in the spleen of Brugia pahangi-infected jirds.
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Antigen specific immunoregulatory phenomena in both human and experimental filariasis are correlated with the presence of circulating microfilariae. Previous studies of inbred jirds infected with Brugia pahangi have demonstrated that the onset of microfilaremia (8-10 weeks post-infection) is associated with a loss of responsiveness to parasite antigens in the spleen, but not the lymph nodes of infected animals. The present experiments defined immunoregulatory phenomena responsible for altered antigen-specific in vitro lymphocyte blastogenesis in the spleen of B. pahangi-infected jirds. Diminished splenic responsiveness to B. pahangi antigens was associated with the presence of a cell capable of suppressing the responsiveness of lymph node cells from infected jirds to parasite antigens. antigen-induced in vitro blastogenic responsiveness of spleen cells from microfilaremic , but not normal animals was restored by depletion of cells adherent to nylon wool or bearing receptors for histamine, peanut agglutinin, soybean agglutinin or jird Fc. The responsiveness of spleen cells from chronically infected (greater than or equal to 20 weeks) animals to mitogens, but not parasite antigens, was enhanced by removal of plastic-adherent cells. The results suggest the involvement of antigen-specific suppressor T cells, in the spleen of B. phangi -infected jirds which are distinct from non-specific suppressor cells previously described in this system. (+info)
Excretory-secretory and somatic antigens in the diagnosis of human filariasis.
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In order to compare the immunodiagnostic value of excretory-secretory (E-S) antigens derived from adult Brugia malayi worms with somatic antigens derived from adults, microfilariae (Mf) and infective larvae (L3) of these parasites, well defined serum pools from patients with filarial (brugia, bancrofti, loa and perstans) and non-filarial (ascaris, stronglyoides, toxocara, echinococcus, cysticercus and schistosoma) helminth infections were tested against antigens derived from these different life cycle stages of B. malayi in a Staphylococcus aureus radioimmunoprecipitation assay (S. aureus RIA). The adult brugia antigens proved significantly more discriminatory than those of the other parasite stages, with the homologous brugia serum pool also showing greater reactivity to adult than to L3 and Mf antigens. Similar results were obtained when individual sera from patients (rather than serum pools) were tested in the same assay. The most surprising finding was the minimal reactivity seen between the adult filarial antigens and the non-filarial serum pools despite the presence in these pools of strong antibody reactivity with their homologous antigens. The reasons underlying the unexpected specificity of this S. aureus RIA for discriminating among sera from filarial and non-filarial infections were analysed qualitatively by immunoprecipitation techniques. It was found that use of the chloramine-T method for radioiodination resulted in preferential labelling of the low molecular weight (mol. wt) proteins (10-70,000 daltons) in the B. malayi adult somatic antigen and that these antigens were bound primarily by the filarial and not the non-filarial serum pools. These findings suggest that lower mol. wt helminth antigens may show greater species specificity than those with higher mol. wt, and those with higher mol. wt, greater cross-reactivity. If substantiated by further analysis, such results would have important implications for the subsequent isolation of diagnostically important filarial parasite antigens. (+info)
Immunoregulation in experimental filariasis. IV. Induction of non-specific suppression following in vitro exposure of spleen cells from infected jirds to Brugia pahangi antigen.
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Studies with inbred jirds chronically infected (greater than 5 months) with Brugia pahangi have demonstrated splenic suppressor cells which modulate in vitro responsiveness to mitogens and parasite antigens. The stimuli which induce suppression were characterized by analysing the effect of activated cells from inbred normal or B. pahangi-infected jirds on the PHA and PWM responsiveness of cultures on normal cells. Regulatory cells were stimulated in vitro with concanavalin A (Con A; 5 micrograms/ml) or an extract of adult B. pahangi (20 micrograms/ml) for 72 hr and irradiated (1500 rads) prior to cocultivation with normal cells. Addition of Con A-activated normal spleen cells to normal cells produced moderate suppression of PHA and enhancement of PWM responsiveness. However, Con A-stimulated spleen cells from infected animals consistently suppressed both the PHA and PWM responsiveness of normal cells by 80-90%. Spleen cells from chronically infected jirds were also induced by B. pahangi antigen to suppress both the PHA and PWM responsiveness of normal lymphocytes. In contrast, spleen cells from animals 3-15 weeks after infection and lymph node cells from all time points were capable of suppressing only PWM responses when stimulated by antigen. Normal spleen cells were not induced by B. pahangi antigens to exhibit immunoregulatory activity. The suppression mediated by antigen-induced spleen cells from chronically infected jirds was partially or totally alleviated by removal of non-specific suppressor cells which are plastic adherent and cyclophosphamide-sensitive, or by removal of antigen-specific suppressor cells which bear receptors for histamine. the results suggest the involvement of regulatory cell circuits in experimental filarial infections. (+info)
Brugia pahangi: serum-dependent cell-mediated reactions to sheathed and exsheathed microfilariae.
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The immune mechanisms operating on the sheath and the cuticle of the Brugia pahangi microfilariae have been studied in vitro. The intact and exsheathed parasites were used for this purpose with serum from albino rats immunized with sonicated homogenates of the parasites as the source of antibodies. The IgG component of the serum was found to promote adherence of rat leucocytes and death of the sheathed and exsheathed parasites in presence of fresh normal serum. EDTA and EGTA abolished the adherence activity suggesting the involvement of complement components via the classical pathway. Both macrophages and neutrophils participate in this reaction. Eosinophils exhibit marginal activity only on exsheathed parasites. The intensity of adherence and killing by neutrophils in the presence of immune serum was greater with the exsheathed microfilariae than with the sheathed ones. (+info)
Activation of jird (Meriones unguiculatus) macrophages by the filarial parasite Brugia pahangi.
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Peritoneal macrophages from Mongolian jirds (Meriones unguiculatus) with either lymphatic or intraperitoneal infections of Brugia pahangi were studied to determine the effects of infection on macrophage function and morphology. Macrophages were collected at 40, 90, 140, and 200 days after inoculation of infective third-stage larvae and assayed for phagocytic and bactericidal activity by the acridine orange method and for morphological changes by light and electron microscopy. Significant increases in phagocytic and microbicidal activity (P less than or equal to 0.01) were observed in peritoneal macrophages collected from jirds with intraperitoneal infections when compared with peritoneal macrophages from jirds with lymphatic infections and resident peritoneal macrophages from normal, noninfected jirds. Morphological changes in peritoneal macrophages from jirds with intraperitoneal infections were similar to those found in thioglycolate-elicited macrophage populations. Granuloma formation was also observed in the peritoneal cavities of intraperitoneally infected jirds. The peritoneal cavity may serve as a model to study cell-worm interactions in filarial nematode infections. (+info)
Effect of cyclophosphamide on the immune responsiveness of jirds infected with Brugia pahangi.
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The in vitro immune responsiveness of lymphocytes from Brugia pahangi-infected jirds was examined after serial administration of cyclophosphamide (20 mg/kg). Cyclophosphamide had no effect on parasite burdens, anti-B. pahangi antibody titers, or suppressed spleen cell reactivity to B. pahangi antigens. Cyclophosphamide restored cellular responsiveness to the mitogens phytohemagglutinin, concanavalin A, and pokeweed mitogen. (+info)
Serosuppression in experimental filariasis.
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Both antigen specific and non-specific immunoregulation by cells have been described in jirds infected with Brugia pahangi, but the contribution of serum factors to immunoregulatory phenomena in this infection has not been examined. The present study determined the effect of serum from normal or B. pahangi infected jirds on the mitogen responsiveness of spleen cells from uninfected animals and on the antigen responsiveness of lymph node cells (LNC) from infected jirds. Addition of heat-inactivated jird serum to cultures of cells supplemented with 1% fetal bovine serum demonstrated that serum from chronically infected (greater than or equal to 20 weeks post-infection), but not normal jirds consistently suppressed responsiveness of LNC from infected jirds to B. pahangi extracts in a dose-dependent manner (0.25%-1% concentration). A comparison of sera from jirds at different times post-infection demonstrated that sera (1%) from chronically infected (30 weeks; 100% suppression), but not acutely infected (4 weeks; 0% suppression) or recently microfilaremic (10 weeks; 11% suppression) animals were capable of suppressing antigen reactivity of LNC. In contrast, the inhibitory effect of serum on lymphocyte reactivity to the mitogens, PHA and PWM, was observed intermittently throughout the course of the infection and was less than the effect of chronic serum on antigen responsiveness. The B. pahangi antigen response of spleen cells from infected jirds depleted of suppressor cells by fractionation over nylon wool was also inhibited by chronic sera. Following fractionation of chronic sera by Sephadex G-200 chromatography, suppressor activity was observed in the void volume and IgG peaks. Suppressor activity was not associated with protein A, anti-jird Ig, or B. pahangi antigen bound fractions, nor with polyethylene glycol precipitable material. (+info)
The presence of blocking factors in Brugia malayi microfilaraemic patients.
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Serum from microfilaraemic patients have been shown to be unable to promote the antibody-dependent, cell-mediated adherence reaction to infective larvae of Brugia malayi in vitro. In this study, it was found that peripheral leucocytes from microfilaraemic patients were also incapable of promoting the adherence reaction even when incubated with serum of tropical pulmonary eosinophilia (TPE) patients. The TPE sera would normally promote the most intense adherence reaction. It was further shown that preincubation of normal human peripheral leucocytes with sera of microfilaraemic patients would similarly render them incapable of adherence. Such preliminary studies suggest that blocking factors may be present in microfilaraemic patients. (+info)