Immunogenicity of haptenated schistosomula in vitro

Skin-stage schistosomula of Schistosoma mansoni modified with 2,4,6-trinitrophenyl (TNP) induce primary anti-TNP plaque-forming cell (PFC) responses in normal mouse spleen cells in vitro. The PFC are TNP-specific, and the response is dependent on adherent cells and T lymphocytes. In contrast, comparably haptenated lung stage larvae are weakly or nonimmunogenic in this system, and their inability to stimulate anti-TNP PFC cannot be attributed to a toxic or suppressive effect. These observations suggest that maturation of schistosomula in vivo is accompanied by a decline in their immunogenicity, which, along with other adaptive mechanisms, may promote the survival of parasites in the host environment.

Schistosomiasis: immunologic properties of developing schistosomula

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Cell-mediated cytotoxicity to Trypanosoma cruzi. II. Antibody-dependent killing of bloodstream forms by mouse eosinophils and neutrophils

Mouse mononuclear cells, neutrophils, and eosinophils were tested for their capacity to mediate antibody-dependent cytotoxicity against bloodstream trypomastigotes of Trypanosoma cruzi. Granulocyte populations were found to be far more effective than nonadherent mononuclear cells in an in vitro assay in which the number of motile parasites was measured. Eosinophils and neutrophils were observed to be equally efficient on a cell-per-cell basis in killing the trypomastigotes. These results were verified in parallel experiments in which trypomastigotes, after incubation with antibody and effector cells, were reinjected into susceptible mice and the survival of the animals was determined.

Transformation of hemopoietic stem cells by phytohemagglutinin (PHA) II. Mechanism of action

It has long been known that phytohemagglutinin (PHA) stimulates transformation and growth of immune competent lymphocytes. Lymphoid cell colonies have previously been shown in the spleen with PHA treated lymph node cells from donor mice were injected into irradiated mice. This communication reports the results of in vivo effects of PHA stimulation on agar colony forming units and spleen colony forming units (CFU). C3H/Hej mice injected with 1 ml of PHA-M were found to secrete colony stimulating factors (PHA-CSF) which lead to an increase in the number of agar colony forming units (granulopoiesis). Serum obtained on day 6 after PHA injection showed enhanced granulopoiesis which was four times higher than in the controls. It was found that 1.0 ml and 0.15 ml of PHA-CSF were more effective in promoting the growth of agar colony forming units in agar plates. Intravenous injection of PHA increased the number of spleen-as well as agar colony forming units (CFU). Day 3 appeared to be optimal for in vivo effects of PHA on granulopoietic cells. An increase in the colony forming units was obtainable when previously treated bone marrow and spleen cells taken on day 3 were injected into irradiated mice. There was a fourfold increase of the colony forming units (CFUs) in the spleen and a twofold one in bone marrow cells. As compared to the controls, the increase in agar colony forming units (CFUc) of bone marrow was fourfold and that of the spleen tenfold. On day 5 some effect was still noticeable but it was lower than on day 3. On weight and cell count basis it was found that on day 6 PHA had a significant in vivo effect on the spleen. On the basis of our findings it can be concluded that PHA supports the survival of transplanted stem cells by stimulating their differentiation into unipotent erythroid progenitor cells. It may also be concluded that PHA activates the immune competent stem cells (mostly T lymphocytes) and displays a supporting function for a better stem cell survival and differentiation into the erythroid progenitor cells. The activated lymphocytes secrete a colony-stimulating like factor which stimulates granulopoiesis and also helps in the differentiation of the stem cells.

Enzymatic treatment transforms trypomastigotes of Trypanosoma cruzi into activators of alternative complement pathway and potentiates their uptake by macrophages

In the absence of bound antibody, trypomastigote bloodstream forms of Trypanosoma cruzi fail to activate the alternative complement pathway. We now demonstrate that treatment with trypsin and, to a lesser extent, with sialidase converts these protozoa into activators of the pathway, as judged by their lysis in normal sera or sera genetically deficient in fourth or second component of complement (C4 or C2) and their Mg2+-dependent consumption of C3 as measured by crossed immunoelectrophoresis. In addition, after pretreatment with enzyme and incubation in C5-deficient serum, trypomastigotes were shown to possess both C3 and properdin factor B (B) on their surface as judged by immunofluorescence. Requirement for the late components C5-C9 was suggested by the failure of C5-deficient sera to lyse trypsin-treated parasites. The inability to activate the alternative complement pathway was regained by these organisms after incubation in vitro. This restoration of insusceptibility was inhibited when puromycin was included in the culture medium. Treatment of the trypomastigotes with trypsin also potentiated their uptake by mouse peritoneal macrophages without apparent interference with their capacity to differentiate and multiply inside the cell. These findings suggest that untreated trypomastigotes normally escape recognition by the alternative pathway in vivo because of the presence on their surface of trypsin- and sialidase-sensitive regulatory molecules, the expression of which is dependent on protein synthesis.

Studies of the antibody-dependent killing of schistosomula of Schistosoma mansoni employing haptenic target antigens. I. Evidence that the loss in susceptibility to immune damage undergone by developing schistosomula involves a change unrelated to the masking of parasite antigens by host molecules

A method was developed for coupling a hapten, trinitrophenyl (TNP), to the surface of schistosomula of Schistosoma mansoni which results in a minimal loss in their viability as judged by morphological examination in vitro and survival after injection in vivo. Skin-stage (3-h-old) and lung-stage (5-d-old) schistosomula surface labeled in this manner were then compared for their susceptibility to killing by anti-TNP antibody-dependent effector mechanisms both in vivo and in vitro. TNP skin-stage larvae were readily rejected in mice actively immunized against TNP bovine gamma globulin and were highly susceptible to anti-TNP-dependent killing mediated either by complement or purified human eosinophils in vitro. In contrast, TNP-lung-stage schistosomula, which were shown by microfluorimetry to bind anti-TNP antibody to approximately the same extent as skin-stage schistosomula, were found to be resistant to killing by the same in vivo and in vitro mechanisms. These findings suggest that the insusceptibility of postskin-stage schistosomula to antibody-dependent killing must result at least in part from an intrinsic structural change in the integument of the parasite and cannot be caused solely by the masking of parasite antigens by acquired host molecules, a mechanism of immune evasion previously proposed for schistosomes.

Specificity of alloreactive T lymphocytes that adhere to lung stage schistosomula of Schistosoma mansoni

Alloreactive T lymphocytes generated against MHC antigens have previously been shown to adhere to lung stage schistosomula of S. mansoni because of the host MHC products known to be present on the surface of the parasites. In experiments reported here, the cells in this adherent population were shown to consist of Ly-2 positive, Thy-1 positive lymphocytes and to react specifically with products of the K and D but not the I region of the MHC. These results strengthen previous findings suggesting that the adherent lymphocytes are CTL.

Specificity of alloreactive T lymphocytes that adhere to lung stage schistosomula of Schistosoma mansoni

Alloreactive T lymphocytes generated against MHC antigens have previously been shown to adhere to lung stage schistosomula of S. mansoni because of the host MHC products known to be present on the surface of the parasites. In experiments reported here, the cells in this adherent population were shown to consist of Ly-2 positive, Thy-1 positive lymphocytes and to react specifically with products of the K and D but not the I region of the MHC. These results strengthen previous findings suggesting that the adherent lymphocytes are CTL.

Newly transformed schistosomula spontaneously lose surface antigens and C3 acceptor sites during culture

The binding of rat anti-schistosome antibody and rat C3 to the surface of newly transformed schistosomula of S. mansoni was measured by quantitative immunofluorescence during the first 48 hr of their development in vitro. Schistosomula, cultured in media either with or without serum, lost antibody or C3 from their surface exponentially with a halftime of 5 hr for both labels. The loss of the surface molecules is seen in parasites that are labeled and then cultured as well as in parasites cultured and then labeled, indicating that the labeling procedure itself is not inducing the observed change. This immunochemical modification in the schistosomulum surface appears to be independent of host molecule adsorption and intrinsic to the development of the parasite.

Newly transformed schistosomula spontaneously lose surface antigens and C3 acceptor sites during culture

The binding of rat anti-schistosome antibody and rat C3 to the surface of newly transformed schistosomula of S. mansoni was measured by quantitative immunofluorescence during the first 48 hr of their development in vitro. Schistosomula, cultured in media either with or without serum, lost antibody or C3 from their surface exponentially with a halftime of 5 hr for both labels. The loss of the surface molecules is seen in parasites that are labeled and then cultured as well as in parasites cultured and then labeled, indicating that the labeling procedure itself is not inducing the observed change. This immunochemical modification in the schistosomulum surface appears to be independent of host molecule adsorption and intrinsic to the development of the parasite.

Purification of rodent eosinophils on discontinuous metrizamide gradients

Methods are described for the purification of rat and mouse eosinophils. Peritoneal exudate cells obtained from Schistosoma mansoni- or Trichinella spiralis-infected mice were plated on plastic dishes, and the nonadherent cells were centrifuged over discontinuous hypertonic metrizamide gradients. Approximately 41% of those eosinophils present in the original preparations were recovered from the interfaces between 20% and 22% metrizamide at an average of 88% purity. Peritoneal cells obtained from either uninfected or S. mansoni-infected rats were placed directly onto metrizamide gradients. After centrifugation, essentially all eosinophils present in the original preparations were recovered at the interface between 18.5% and 22.5% metrizamide, with an average of 80% purity. These methods for eosinophil purification have proven to be reproducible and to yield cells which are morphologically preserved and functional, as demonstrated by their ability to respond to a chemotactic stimulus.

Major histocompatibility complex products restrict the adherence of cytolytic T lymphocytes to minor histocompatibility antigens or to trinitrophenyl determinants on schistosomula of Schistosoma mansoni

We have previously shown that schistosomula passaged through mice acquire histocompatibility (H) antigens that can be recognized either by alloantibody or by alloreactive cytolytic T lymphocytes (CTL). The latter specifically adhere to but fail to damage the parasite. In this paper we describe the use of trinitrophenyl (TNP)-labeled schistosomula to show that the adherence of CTL with specificity for TNP-modified syngeneic cells is restricted by the major histocompatibility complex (MHC) in a fashion similar to that seen in the lysis of TNP-labeled tumor targets. Thus, these CTL adhere only to schistosomula that have both the appropriate H antigens and TNP determinants on their surface, and not to schistosomula bearing either of these antigens by themselves. We note a significant degree of adherence to schistosomula bearing TNP determinants and H antigens allogeneic to the CTL. Anti-minor H antigen CTL are also restricted by the MHC in their adherence; thus, they only adhere to schistosomula that carry both the major and minor H antigens of the stimulator cells. These antigens can be acquired either by a single passage in vivo of schistosomula through congenic strains that possess both the relevant antigens or by sequential passage through two different strains, each contributing one of the antigens in question.

Potentiation of schistosome granuloma formation. By lentinan--a T-cell adjuvant

Lentinan is a fungal polysaccharide which acts as a T-cell adjuvant. When this glucan was administered to thymus-intact mice by intraperitoneal injection, conspicuously enlarged lung granulomas formed in response to either Schistosoma mansoni or S japonicum eggs or to antigen-coated polyacrylamide beads. Liver granulomas in cercaria-induced S mansoni infection were augmented up to eight-fold in volume. By contrast, nude mice showed a complete absence of hypersensitivity granulomas, regardless of whether they received lentinan. Lentinan-potentiated granulomas show a distinctive histopathologic picture characterized by abundant, large, pale-staining macrophages; reduced and redistributed eosinophil populations; and frequent, extensive central necrosis, uncommon in unpotentiated schistosome foci. They also differ in their distributions of egg antigen and of host immunoglobulins. Optimal lentinan effects followed a single 1-mg dose when given to sensitized mice on the day of intravenous challenge with S mansoni eggs rather than at the time of intraperitoneal sensitization or following challenge. This adjuvant appears to act on effector T cells or on macrophages interacting with T cells; its effect on macrophages in a latex bead foreign body granuloma was minimal. A number of other lentinan-associated systemic effects on parasite and host were noted and described, including reduced female schistosome egg output.

Acquisition of murine major histocompatibility complex gene products by schistosomula of Schistosoma mansoni

Schistosoma mansoni schistosomula recovered from the lungs of inbred mice were shown to possess serologically detectable alloantigens on their tegumental surfaces. Using appropriate antisera and infected congenic and recombinant mice as worm donors, gene products of the K and I subregions of the major histocompatibility complex were demonstrated among these alloantigens acquired by the parasites. In contrast, other cell surface alloantigens, such as Thy 1, Ly 1, and H-Y and the serum proteins albumin, C3 and Ig, could not be detected on the surface of lung schistosomula by means of comparable techniques. In another series of experiments, schistosomula recovered from the lungs of mice and reinjected into allogeneic recipients were shown to exchange their alloantigens during an 87-h period of examination. Similarly, lung schistosomula cocultured with allogeneic lymphocytes were shown to acquire major histocompatibility complex (MHC) coded antigens from the cells. It is possible that as acquired host molecules, MHC gene products may disguise the surface of schistosome parasites thereby rendering them insusceptible to immune attack.

Early developmental changes of the schistosomula of Schistosoma mansoni in vitro and in mouse lung

Fresh (3 h) schistosomula of Schistosoma mansoni were obtained by the skin penetration method and injected intravenously into groups of mice either immediately or after 48 h incubation in tissue culture. Schistosomula were then recovered from the lungs 1 to 2 days after injection. The recovery results showed that the ability of uncultured schistosomula to emerge from lung tissue increased with time, became maximal on the 3rd day and diminished thereafter. In contrast, cultured schistosomula were able to emerge from chopped lung at a much earlier time after injection. Fresh schistosomula, as well as those recovered from mouse lungs, were assayed by indirect immunofluorescence for the presence of parasite and host antigens. Similarly, fresh schistosomula which had been incubated in foetal calf serum, with or without mouse red blood cells, were assayed for parasite and host antigens after 3-24 h of culture. Fresh schistosomula expressed parasite antigen with greater intensity than those recovered from mouse lungs and showed no trace of host antigen. Lung schistosomula, on the other hand, expressed less parasite antigen but more red blood cell antigen with increasing time in the host. Schistosomula cultured in the absence of mouse red blood cells expressed only parasite antigen throughout the period in culture, while those cultured in the presence of mouse red blood cells also expressed parasite antigen during the entire period in culture but, in addition, by 24 h host antigen could also be detected. These developmental and adaptational changes may play a role in determining the survival of parasites in the normal or immune host.

Immune responses during human schistosomiasis mansoni. II. Occurrence of eosinophil-dependent cytotoxic antibodies in relation to intensity and duration of infection

Plasma samples from St. Lucians were tested for the presence of antibodies which cooperate in vitro with normal human leukocytes in causing cytotoxic damage to schistosomula of Schistosoma mansoni. The in vitro antibody activity, which has been previously shown to depend on eosinophil effector cells was detected in 56% of the individuals with known, current S. mansoni infections and in 14% of control subjects from the same endemic area. Quantitatively, eosinophil dependent cytotoxic antibody (EDCA) activity, when expressed as the maximum amount of damage to schistosomula induced at high plasma concentration, correlated significantly with the intensity of S. mansoni infection as determined by fecal egg count, the highest levels of activity occurring in patients with stool counts of 60 eggs/ml or greater. In addition, plasma EDCA activity was found to correlate with the in vitro blastogenic responsiveness of patients' lymphocytes to three different parasite antigen preparations. In contrast, titrations of EDCA activity failed to reveal a relationship between EDCA titer and the most recent egg count performed on each subject. However, a significant correlation was observed when titers were compared to egg counts averaged over a 3-year period. Neither maximal EDCA activity nor titer was found to correlate with the duration of known schistosome infection.

Receptors for C3 on rat peritoneal mast cells

Purified rat peritoneal mast cells adhere to schistosomula of Schistosoma mansoni which have been pre-incubated in fresh normal rat serum. This cytoadherence reaction is dependent on complement and in particular on components of the alternative pathway. Since antibodies to rat C3 but not IgG block the attachment of the cells to the complement-treated larvae, it appears that C3-specific receptors on the mast cell surface are responsible for the adherence phenomenon. These receptors can also be demonstrated by the rosetting of mast cells with rat complement-treated zymosan particles or fluoresceinated bacteria. The key properties of the receptors are their specificity for homologous (rat) complement, their sensitivity to digestion with trypsin, and their functional dependence on Mg++ ions. Thus, the rat mast cell receptors share many of the characteristics of the C3 receptors previously identified on monocytes, macrophages, and polymorphonuclear leukocytes.

Failure of plasma from human schistosomiasis mansoni patients to protect mice from Schistosoma mansoni cercarial challenge

Plasma samples obtained from patients with well defined Schistosoma mansoni infections, or control subjects, were passively transferred to CF1 mice. Three, 12, or 24 hours after passive transfer, the recipient and control mice were challenged with either 200 or 600 live cercariae, and the adult worm burdens or schistosomula lung recoveries, respectively, were determined 7 weeks or 6 days after challenge. None of the human plasmas afforded the recipient mice protection against the development of schistosomes. Worm and larval yields were equivalent in all cases, even though many of the patient plasmas were shown, as assessed by an in vitro eosinophil-dependent cytotoxic antibody assay, to contain high levels of antischistosomular antibody.

A lung model of schistosome immunity in mice

When mice are challenged intravenously with schistosomula of Schistosoma mansoni, host cell reaction and parasite attrition proceed entirely in the lung, where these events can be followed by quantitative histology and worm recovery. In nonimmune animals the destruction of schistosomula in the lungs proceeds gradually, resulting in the elimination of about 80% of the challenge organisms after 6 days. Cell reaction begins promptly, as evidenced by the appearance of neutrophilic foci around many of the lung schistosomula within 30 minutes after injection, and results in increasing numbers of damaged organisms and residual inflammatory foci 24 hours and 6 days later, respectively. In contrast, when schistosomula are injected into mice immune by virtue of an established S. mansoni infection, parasite destruction is augmented and accelerated, a process already evident by 24 hours. By the sixth day, 98% of the challenge organisms have been eliminated, a substantially greater reduction in parasite survival than that occurring in the normal host. This increased attrition of schistosomula is also reflected in the decreased numbers of parasites recovered from minced lung tissue of immune mice 6 days after challenge. Immune cellular inflammatory reactions to schistosomula are, likewise, greatly intensified and can be readily distinguished from those of normal mice by the proportions of parasites involved and by the large numbers of eosinophils surrounding them. In some instances, degranulation of eosinophils onto the parasite tegument is observed. Schistosomula cultured for 24 or 44 hours in a medium containing mouse red blood cells elicit significantly less cellular reaction and show greater survival in the lungs of immune animals than do freshly derived schistosomula. It would therefore appear that the susceptibility of maturing schistosomes to immune cellular attack is limited to the first day or two after their metamorphosis from cercariae. These observations form the framework of a new in vivo model for analyzing the dynamics of the cellular and humoral processes involved in the immune destruction of a metazoan parasite. The model also lends itself to studies of the immunologic interrelationships between innate and acquired resistance to infection with schistosomes, as well as the mechanisms by which these parasites evade the host immune response.

Host antigens and parasite antigens of murine Schistosoma mansoni

An indirect fluorescent antibody technique was used to detect mouse host antigens and parasite antigens on the surface of Schistosoma mansoni. A rabbit anti-mouse rbc antiserum to detect host antigens, and serum from mice immune to S. mansoni was used to detect parasite antigens. Schistosomula prepared after penetration of isolated mouse skin did not possess host antigens but bound antibody from immune serum (immune antibody); schistosomula recovered from the lungs of mice five days after infection possessed host antigens and failed to bind immune antibody. In contrast, schistosomula recovered from the skin of normal or immune mice three and 20 hours after cercarial penetration, adult worms, and cryostat sections of adult worms, were positive for host antigens but also bound immune antibody. Strong binding of immune antibody only occurred with the cryostat sections. Anti-schistosome antibody can therefore bind to schistosomes in the presence of host antigen. The lung forms of schistosomula however, may have different surface properties as there is no evidence that immune antibody binds to these forms.

Eosinophil-enriched inflammatory response to schistosomula in the skin of mice immune to Schistosoma mansoni

Exposure of the mouse skin to Schistosoma mansoni cercariae gives rise to acute, exudative inflammation in both normal and immune mice, but the immune response is anamnestically accelerated and is oesinophil-enriched, thereby enhancing opportunities for tegumental contact of schistosomula with host leukocytes, particularly with eosinophils. Many of the inflammatory changes occurring within the first 48 hours after exposure are due to cercarial products, e.g., "penetration tracts," but some remain demonstrable when schistosomula metamorphosed in vitro are injected intradermally and are therefore directed against the schistosomula themselves, such as the leukocyte "streaming patterns" seen in their pathways. In contrast to earlier observations in primates, cellular responses to schistosomula in the mouse lung 4 days after penetration are minimal in either normal or immune mice. Thus, immune cellular responses to schistosomula in mice are limited to an early time period after cercarial penetration and are morphologically suggestive of an antibody-mediated response rather than of delayed hypersensitivity. Our observations complement earlier evidence suggesting that antibody-mediated host leukocyte contact with schistosomula initiates the killing of challenge parasites in immune mice, with the eosinophil probably playing a crucial role.

Passive transfer of acquired resistance to Schistosoma mansoni in laboratory mice

Serum taken from mice 12-15 weeks after a primary infection of Schistosoma mansoni transfers to normal recipients a partial resistance to subsequent schistosome challenge. The transfer of immunity is evident not only in the reduced recovery of mature parasites from the liver, but also in the diminished numbers of invading schistosomula recovered of resistance equivalent on average to 47% of that found in actively immunized animals, the results suggest that humoral factors play a major role in the effector mechanism of schistosome immunity.

Partial isolation of a membrane antigen which induces the formation of antibodies lethal to schistosomes cultured in vitro

Fractions of adult schistosomes (S. mansoni) were tested for their ability to absorb an IgG antibody activity which appears in the sera of rats and Rhesus monkeys infected with the parasite and is lethal to schistosomula cultured in vitro. The same fractions were tested for their immunogenicity in raising lethal antibody when administered to rats in Freund's adjuvant. The results of these experiments indicated that an antigen which both absorbs and induces the formation of lethal antibody is present almost entirely in the water-insoluble portion of adult schistosome homogenates. The antigen appears to be tightly bound to this membrane fraction since the use of strong anionic detergents is necessary in its extraction. Membranes solubilized in sodium dodecyl sulphate were fractionated by gel filtration on Sephadex columns equilibrated with the detergent. The same specific Sephadex fraction was shown to absorb both rat and Rhesus monkey lethal antibodies as well as induce the antibody when administered to rats. Further purification and analysis suggested that the immunogen was one of four proteins with molecular weights estimated between 21,000 and 33,000 Daltons.

Rats vaccinated with partially purified antigen developed levels of lethal antibody similar to those found in animals immune to challenge through previous exposure to the parasite, yet were themselves only marginally resistant to infection. These results indicate that while clearly toxic to schistosomula grown in vitro, lethal antibody operating on its own in vivo is incapable of mediating the rejection of schistosome infections.