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.

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.

Effect of Haptens on the Reaction of Anti-Idiotype Antibody with a Mouse Anti-Phosphorylcholine Plasmacytoma Protein

In a radioimmune assay under conditions of excess antigen, the binding of a mouse antiphosphorylcholine plasmacytoma protein by anti-idiotype antibody is partially inhibited by phosphorylcholine and related haptens. The effect of these haptens on the idiotype correlates with the affinity with which they are bound by the plasmacytoma protein.

Reconstitution from Subunits of the Hapten Binding Sites and Idiotypic Determinants of Mouse Anti-Phosphorylcholine Myeloma Proteins

Reconstitution experiments were employed to investigate the structure of the hapten binding sites and idiotypic determinants of mouse myeloma proteins with antibody specificity for phosphorylcholine. Quantitative reconstitution of both the phosphorylcholine binding affinity and idiotypic reactivity of these immunoglobulins was shown to require specific heavy and light chain combinations. Interaction of myeloma protein with hapten (phosphorylcholine or choline) had no effect on the expression of the idiotype. The subunits of the immunoglobulins possessing in common an idiotype and affinity for phosphorylcholine reconstituted indistinguishable antibodies. In addition, it was shown that the light chains of the proteins belong to the same κ subgroup. Since these indistinguishable immunoglobulins are found repeatedly, they may represent the expression of the same heavy and light chain variable region genes out of a small number present in the BALB/c germ-line.

Hapten Binding Studies on Mouse IgA Myeloma Proteins with Antibody Activity

Five mouse IgA myeloma proteins (S23, S63, S107, S129, J539) with antibody specificities for either phosphorylcholine, ε-DNP-caproic acid or galactoside derivatives were studied in terms of their binding of these ligands. The immunoglobulins appeared to be homogeneous with respect to their affinity for hapten and had association constants between 2 × 103 and 105 liters/mol as determined from equilibrium dialysis measurements. Binding activity was associated with the Fab fragment of each IgA. By means of a membrane filter assay, unfractionated S107 protein in serum as well as the reduced and alkylated monomer purified by immunoadsorption was shown to have two sites per 156,000 unit molecular weight. Digestion of the monomer with trypsin gave a Fab fraction in 64% yield with one site per 53,000 molecular weight. However, protein purified by procedures involving chromatography, gel filtration and repeated dialysis steps gave fractional numbers of binding sites, a finding which suggests that mouse IgA's are unusually sensitive to denaturation.

The Subunit Structure of Mouse IgA

Mouse IgA myeloma proteins have been studied for the structure of their polypeptide chains and papain fragments. Heavy and light chains, Fab and Fc fragments were shown to have molecular weights closely corresponding to their IgG equivalents and the mass ratio of Fab and Fc fragments indicate the presence of two Fab and one Fc fragments per IgA monomer. The results, taken together with the available hapten-binding data, suggest that a single light-heavy chain pair constitute a hapten-binding site in IgA. In addition, structural studies performed on normal mouse IgA indicate the presence in their structure of dimerized light chain as had been previously reported for IgA myeloma proteins.