In vitro modelling of rat mucosal mast cell function in Trichinella spiralis infection

Intestinal infection with the parasitic nematode, Trichinella spiralis, provides a robust context for the study of mucosal mast cell function. In rats, mucosal mast cells are exposed to parasites during the earliest stage of infection, affording an opportunity for mast cells to contribute to an innate response to infection. During secondary infection, degranulation of rat mucosal mast cells coincides with expulsion of challenge larvae from the intestine. The goal of this study was to evaluate the rat bone marrow-derived mast cells (BMMC) and the rat basophilic leukaemia cell line (RBL-2H3) as models for mucosal mast cells, using parasite glycoproteins and antibody reagents that have been tested extensively in rats in vivo. We found that BMMC displayed a more robust mucosal phenotype. Although T. spiralis glycoproteins bound to mast cell surfaces in the absence of antibodies, they did not stimulate degranulation, nor did they inhibit degranulation triggered by immune complexes. Parasite glycoproteins complexed with specific monoclonal IgGs provoked release of rat mast cell protease II (RMCPII) and β-hexosaminidase from both cell types in a manner that replicated results observed previously in passively immunized rats. Our results document that RBL-2H3 cells and BMMC model rat mucosal mast cells in the contexts of innate and adaptive responses to T. spiralis.

Contributions of conventional and heavy-chain IgG to immunity in fetal, neonatal, and adult alpacas

In addition to conventional immunoglobulins, camelids produce antibodies that do not incorporate light chains into their structures. These so-called heavy-chain (HC) antibodies have incited great interest in the biomedical community, as they have considerable potential for biotechnological and therapeutic application. Recently, we have begun to elucidate the immunological functions of HC antibodies, yet little is known about their significance in maternal immunity or about the B lymphocytes that produce them. This study describes the application of isotype-specific reagents toward physiological assessments of camelid IgGs and the B cells that produce them. We document the specificities of monoclonal antibodies that distinguish two conventional IgG1 isotypes and two HC IgG3 variants produced by alpacas. Next, we report that the relative concentrations of five isotypes are similar in serum, milk, and colostrum; however, following passive transfer, the concentrations of HC IgG2 and IgG3 declined more rapidly than the concentration of conventional IgG1 in the sera of neonates. Finally, we assessed the distribution of B cells of distinct isotypes within lymphoid tissues during fetal and adult life. We detected IgG1, IgG2, and IgG3 in lymphocytes located in lymph node follicles, suggesting that HC B cells affinity mature and/or class switch. One IgG3 isotype was present in B cells located in ileal Peyer's patches, and one conventional IgG1 isotype was detected in splenic marginal zone B cells. Our findings contribute to the growing body of knowledge pertaining to HC antibodies and are compatible with functional specialization among conventional and HC IgGs in the alpaca.

Immunity to Trichinella spiralis muscle infection

Trichinella spiralis larvae establish chronic infections in skeletal muscles of immunocompetent hosts. Muscle infection is crucial to transmission and survival of the parasite in nature. Chronic infections by this highly immunogenic parasite are associated with modulation or escape from potentially destructive immune responses. This review summarizes our current knowledge of immunity to muscle infection with T. spiralis.

Application of monoclonal antibodies in functional and comparative investigations of heavy-chain immunoglobulins in new world camelids

Of the three immunoglobulin G (IgG) isotypes described to occur in camelids, IgG2 and IgG3 are distinct in that they do not incorporate light chains. These heavy-chain antibodies (HCAbs) constitute approximately 50% of the IgG in llama serum and as much as 75% of the IgG in camel serum. We have produced isotype-specific mouse monoclonal antibodies (MAbs) in order to investigate the roles of HCAbs in camelid immunity. Seventeen stable hybridomas were cloned, and three MAbs that were specific for epitopes on the gamma chains of llama IgG1, IgG2, or IgG3 were characterized in detail. Affinity chromatography revealed that each MAb bound its isotype in solution in llama serum. The antibodies bound to the corresponding alpaca IgGs, to guanaco IgG1 and IgG2, and to camel IgG1. Interestingly, anti-IgG2 MAbs bound three heavy-chain species in llama serum, confirming the presence of three IgG2 subisotypes. Two IgG2 subisotypes were detected in alpaca and guanaco sera. The MAbs detected llama serum IgGs when they were bound to antigen in enzyme-linked immunosorbent assays and were used to discern among isotypes induced during infection with a parasitic nematode. Diseased animals, infected with Parelaphostrongylus tenuis, did not produce antigen-specific HCAbs; rather, they produced the conventional isotype, IgG1, exclusively. Our data document the utility of these MAbs in functional and physiologic investigations of the immune systems of New World camelids.

Molting, ecdysis, and reproduction of Trichinella spiralis are supported in vitro by intestinal epithelial cells

Trichinella spiralis is an obligate parasite of animals that has an unusual intracellular life cycle. Investigation of parasitism at the cellular and molecular levels has been challenging because of a shortage of tools for in vitro cultivation of T. spiralis. We have found that T. spiralis larvae molt, ecdyse, develop to adulthood, and reproduce when they are inoculated onto cultured intestinal epithelial cells. Initially, larvae invade and migrate through cells in a monolayer (T. ManWarren, L. Gagliardo, J. Geyer, C. McVay, S. Pearce-Kelling, and J. Appleton, Infect. Immun. 65:4806-4812, 1997). During prolonged culture in Caco-2 epithelial cells, L1 larvae molted and ecdysed with efficiencies as high as 50%. Molting and ecdysis in vitro required entry of the parasite into cells; conditions that prevented entry into cells also prevented ecdysis. When larvae were inoculated at a low density and cultured for 5 to 9 days, as many as 50% of the larvae developed to adult stages. Low numbers of mature male worms with copulatory appendages were observed in these cultures. The majority of worms that survived for five or more days were unfertilized females. Low-density cultures supported development of female worms with embryos at rates of 4 to 5%. These results show that the intestinal life cycle of T. spiralis can be supported entirely by host epithelial cells. Our model should allow more detailed investigation of intracellular parasitism by T. spiralis.

A pivotal role for glycans at the interface between Trichinella spiralis and its host

The nematode Trichinella spiralis demonstrates a simple but novel parasitic life-cycle, completing all of its development in intracellular habitats. This feature of the life-cycle has challenged investigators aiming to elucidate mechanisms of parasitism. Investigations of immunity showed a dominant influence of N-glycans in the responses to larval T. spiralis. It has become evident that novel glycans are positioned to play important roles in parasitism, as well as immunity, in infection with this nematode.

Invasion of epithelial cells by Trichinella spiralis: in vitro observations

It has been known for many years that Trichinella spiralis initiates infection by penetrating the columnar epithelium of the small intestine, however, the mechanisms used by the parasite in the establishment of its intramulticellular niche in the intestine are unknown. The recent demonstration that invasion also occurs in vitro when infective larvae of T. spiralis are inoculated onto cultures of epithelial cells provides a model that allows the direct observation of the process by which the parasite recognizes, invades and migrates within the epithelium. The finding that penetration of the cell membrane or induction of plasma membrane wounds by larvae do not always result in invasion argue in favor of some kind of host-parasite communication in successful invasion. In this sense, the in vitro model of invasion provides a readily manipulated and controlled system to investigate both parasite, and host cell requirements for invasion.

Phosphorylcholine-containing N-glycans of Trichinella spiralis: identification of multiantennary lacdiNAc structures

Although the presence of phosphorylcholine (PC) in Trichinella spiralis is well established, the precise structure of the PC-bearing molecules is not known. In this paper, we report structural studies of N-glycans released from T.spiralis affinity-purified antigens by peptide N-glycosidase F. Three classes of N-glycan structures were observed: high mannose type structures; those which had been fully trimmed to the trimannosyl core and were sub-stoichiometrically fucosylated; and those with a trimannosyl core, with and without core fucosylation, carrying between one and eight N-acetylhexosamine residues. Of the three classes of glycans, only the last was found to be substituted with detectable levels of phosphorylcholine.

Larvae-induced plasma membrane wounds and glycoprotein deposition are insufficient for Trichinella spiralis invasion of epithelial cells

Trichinella spiralis L1 larvae infect susceptible hosts by invading epithelial cells that line the small intestine. Invasion also occurs in vitro when larvae are inoculated into cultures of epithelial cells from several different animal species. To further investigate the mechanism of invasion, we studied the interaction of larvae with the rat epithelial cell line IEC-6. Larvae did not invade IEC-6 cells, but did cause the cells to take up parasite glycoproteins. Glycoprotein bearing cells remained viable and were detectable in monolayers for as long as 24 h, suggesting that the glycoproteins were not toxic for cells. Immunofluorescence revealed that parasite glycoproteins localized in the nuclei, mitochondria and cytoplasm and we found evidence for selection of certain molecules between nuclear and cytoplasmic compartments. Using fluorescent dextrans as fluid phase markers we found 17-38% of the cells in inoculated monolayers were engorged with dextran and that dextran was free in the cytoplasm. Increased dextran uptake was not lethal, required the presence of activated larvae, and was often associated with uptake of parasite glycoproteins. These observations suggest that larvae caused plasma membrane wounds. Our results showed that neither delivery of glycoproteins nor mechanical wounding is sufficient to allow entry of the parasite into resistant epithelial cells. Because both invasion-resistant and susceptible epithelial cells undergo non-lethal wounding, we propose that larvae-induced injury to epithelial cells may result in release of cell-specific mediators that signal larva to invade a particular cell line or, alternatively, to ignore it.

Dominance of immunoglobulin G2c in the antiphosphorylcholine response of rats infected with Trichinella spiralis

The antibody response to the L1 stage of Trichinella spiralis has been described as biphasic. Worms resident in the intestine during the first week of infection stimulate an antibody response against a subset of larval proteins. L1 larvae in the muscle at the end stage of infection stimulate a second antibody response against tyvelose-bearing glycoproteins. Antityvelose antibodies protect rats against challenge infection with larvae. The aim of this study was to characterize the rat B-cell response against larval antigens during the intestinal phase of T. spiralis infection and to test the antiparasitic effects of such antibodies. Strain PVG rats were infected orally with 500 larvae. Antibodies specific for phosphorylcholine-bearing proteins of L1 larvae first appeared in serum 9 days postinfection. Absorption experiments showed that the majority of antilarval antibodies produced in rats 16 days after infection with T. spiralis were specific for phosphorylcholine-bearing proteins. A fraction of these antibodies bound to free phosphorylcholine. Immunoglobulin G2c (IgG2c) producing cells in the mesenteric lymph node dominated this early antibody response. IgG2c is associated with T-independent immune responses in the rat; however, a comparison of athymic rats with euthymic controls suggested that only a small fraction of the phosphorylcholine-related antibody response against T. spiralis was T independent. Phosphorylcholine is a common epitope in antigens of bacteria and nematode parasites and has been shown to be a target of protective immunity in certain bacteria. A monoclonal IgG2c antibody was prepared from infected rats and shown to be specific for phosphorylcholine. Monoclonal phosphorylcholine-specific IgG2c failed to protect rats against intestinal infection with T. spiralis. Therefore, our findings do not support a role for phosphorylcholine-bearing antigens in immune defense against T. spiralis; however, the potency of the immune response induced suggests an immunomodulatory role for the lymphocytes involved.

Terminal beta-linked tyvelose creates unique epitopes in Trichinella spiralis glycan antigens

Indirect evidence that the immunodominant N-glycans of the parasite, Trichinella spiralis are capped by novel beta-linked 3,6-dideoxy-D-arabinohexopyranosyl residues (tyvelose, Tyv) was obtained from immunochemical assays employing monoclonal antibodies and synthetic oligosaccharides. Three of four previously characterized monoclonal antibodies generated from the lymphocytes of T.spiralis infected rats bind BSA glycoconjugates bearing the synthetic epitope beta-D-Tyvp(1-->3)-beta-D-GalNAcp but not to the corresponding alpha-D-Tyvp(1-->3)-beta-D-GalNAcp-BSA glycoconjugate. Monosaccharide and disaccharide glycoside inhibition data mirrors the results of the direct binding experiments. The branched tetrasaccharide beta-D-Tyv(1-->3)-beta-D-GalNAcp(1-->4)[alpha-L-Fucp(1 -->3)] beta-D-GalNAcp is the most active synthetic oligosaccharide inhibitor for all four monoclonal antibodies studied, while the corresponding alpha-D-Tyv containing tetrasaccharide and the core trisaccharide beta-D-GalNAcp(1-->4)[alpha-L-Fucp(1-->3)]beta-D-GlcNAcp+ ++ are inactive. The exceptional inhibitory activity of the disaccharide beta-D-Tyvp(1-->3)-beta-D-GalNAcp with one mAb (18H) compared to that of the branched tetrasaccharide beta-D-Tyvp(1-->3)-beta-D-GalNAcp(1-->4)[alpha-L-Fucp( 1-->3)]-beta-D-GlcNAcp is indicative of the presence of linear, nonfucosylated glycan epitopes (beta-D-Tyvp(1-->3)-beta-D-GalNAcp(1-->4) beta-D-GlcNAcp) that lack a fucose residue in one arm of the antigenic, tetra-antennary N-glycan. This observation supports earlier FAB-mass spectrometry evidence for the existence of tetra-antennary, core fucosylated glycans that lack a fucose residue on one of their antennae.

Workshop on a detailed characterization of Trichinella spiralis antigens: a platform for future studies on antigens and antibodies to this parasite

In order to characterize immunodominant components of T. spiralis a workshop was organized. In this the reactivity of monoclonal and polyclonal antibodies, provided by different research groups, towards total extracts from adult, new born larvae and muscle larvae as well as to excretory/secretory components of muscle larvae were tested by ELISA, Western blot and immunoprecipitation assays. As a result of this workshop T. spiralis ML antigens have been classified into eight groups (TSL-1-TSL-8) according to their recognition by monoclonal and polyclonal antibodies. Among them, TSL-1 antigens have been the most extensively characterized both biochemically and immunologically. These antigens are stage specific, originate in the muscle stichosome and are abundant in both E/S and on the larval cuticular surface. The TSL-1 antigens share an immunodominant carbohydrate epitope (tyvelose), which is unique for Trichinella and is not associated with phosphorylcholine. The data collected in this workshop has allowed both the unification of the nomenclature for T. spiralis antigens and their biochemical characterization. It also has provided a platform for further studies on the characterization of other T. spiralis antigens and indeed for other Trichinella species.

The relationship between single radial hemolysis, hemagglutination inhibition, and virus neutralization assays used to detect antibodies specific for equine influenza viruses

Antibodies specific for equine influenza viruses are usually quantified using single radial hemolysis (SRH), hemagglutination inhibition (HI) or virus neutralization (VN). Neutralizing antibodies are thought to provide optimum protection to challenged animals. The purpose of this study was to determine the extent to which SRH and HI assays detect antibodies which neutralize equine influenza viruses. Acute and convalescent sera from 41 horses were analyzed using VN, SRH, and HI assays. These horses were present in a population of Thoroughbred racehorses during an epidemic of upper respiratory tract disease associated with influenza A/equine/Saskatoon/1/91 (H3N8), infections. Concentrations of antibodies binding to influenza A/equine/Kentucky/1/81 (H3N8), A/equine/Miami/1/63 (H3N8), and A/equine/Prague/1/56 (H7N7) were determined. Results of the VN assay were compared with results from the SRH and HI assays for acute antibody levels, changes in antibody concentrations between acute and convalescent sampling, and the occurrence of seroconversion. The correlation between assays for pre-exposure antibody levels ranged from 88% to 96%. The correlation between assays for change in antibody concentration ranged from 83% to 90% for the H3N8 viruses. This study shows that antibody concentrations specific for equine influenza virus, measured using SRH and HI assays, are highly correlated with concentrations detected using a VN assay.

Novel tyvelose-containing tri- and tetra-antennary N-glycans in the immunodominant antigens of the intracellular parasite Trichinella spiralis

The larval stage of the intestinal nematode, Trichinella spiralis, secretes and displays on its cuticle a number of antigenically cross-reactive glycoproteins. These so-called TSL-1 antigens induce a powerful antibody response in parasitized animals. In rats, anti-TSL-1 antibodies mediate a protective immunity that expels invading larvae from the intestine. The vast majority of anti-TSL-1 antibodies are specific for glycans. Although the biological functions of TSL-1 antigens are not known, the powerful effect of glycan-specific antibodies on the intestinal survival of T. spiralis suggests that they play an important role in parasite establishment. Little is known about the structures of the glycans present on the TSL-1 glycoproteins. Recent studies have suggested, however, that the antigens contain very unusual glycans (Wisnewski, N., McNeil, M., Grieve, R.B. and Wassom, D.L., Mol. Biochem. Parasitol., 61, 25-36, 1993). Sugar and linkage analysis of the combined secreted products unexpectedly showed that a major terminal sugar is tyvelose (3,6-dideoxy-D-arabino-hexose; Tyv) which has previously been found only in certain gram-negative bacterial lipopolysaccharides. In this paper, we report the first rigorous structural study of oligosaccharides released from TSL-1 antigens by peptide N-glycosidase F digestion. Using strategies based on fast atom bombardment mass spectrometry (FAB-MS), we have discovered a novel family of tri- and tetra-antennary N-glycans whose antennae are comprised of the tyvelose-capped structure: Tyv1,3GalNAc beta 1,4(Fuc alpha 1,3)GlcNAc beta 1-. Thus a major population of TSL-1 glycans contains clusters of hydrophobic terminal structures which are likely to be highly immunogenic.

Glycans as targets for monoclonal antibodies that protect rats against Trichinella spiralis

We have investigated the role of glycans on Trichinella spiralis antigens in recognition by rat monoclonal antibodies (mAbs) which protect rat pups against challenge with the parasite. In pups born to infected dams or pups passively immunized with mAbs, antibodies eliminate a challenge dose from the intestine within hours ('rapid expulsion'). Because such dramatic protection can be afforded by mAbs, we have sought to characterize the parasite antigens they target. In this report we show that protective antibodies were unable to bind excretory/secretory (ES) antigens deglycosylated with trifluoromethanesulphonic acid (TFMS). In addition, oligosaccharides isolated from glycoproteins by alkaline hydrolysis or peptide: N glycosidase F (PNGase F) digestion were bound by protective, but not non-protective, mAbs. Glycans affinity purified with protective mAb 9D bound to all but one protective mAb. These antibodies have been shown previously to bind to the surfaces of intact larvae, indicating that the glycan is exposed on the parasite surface. Candidate glycans that may be involved in binding protective mAbs have unusual tri- and tetra-antennary structures with terminal tyvelose moieties (Reason et al., Glycobiology, 4, 000-000, 1994). Coating of the larval surface with such glycans may serve to protect the parasite and its secreted products from enzymatic attack as the parasite travels to and resides in its epithelial niche.

Molecular analysis of antigens targeted by protective antibodies in rapid expulsion of Trichinella spiralis

Rapid expulsion is a protective immune mechanism which eliminates as much as 99% of a challenge infection of Trichinella spiralis muscle larvae from the gastrointestinal tract of suckling rats. Protective monoclonal antibodies (mAbs) generated against larval excretory-secretory antigens (ESA) specifically recognize a 45-kDa glycoprotein, gp45, in addition to a distinct profile of other cross-reactive antigens that are also recognized by non-protective mAbs. Recent data indicate that protective mAbs recognize carbohydrate epitopes. To complement biochemical studies on the target(s) of rapid expulsion, we describe here the cloning and characterization of the cDNA, TspE1, which belongs to a multigene family and encodes several larval proteins in the 40-50-kDa range. A second cDNA, TspM6 encodes a 45-kDa antigen and is homologous to the published sequence of gp45. Anti-TspE1 antibodies detected antigens within beta- and gamma-stichocytes while anti-TspM6 antibodies detected antigens within alpha-stichocytes of the secretory organs of muscle larvae. Sequence analysis has provided no functional information on the encoded gene products. Neither recombinant antigen is recognized by the mAbs but native parasite molecules with peptide homology to both the TspE1 and TspM6 recombinant antigens bear the glycan recognized by the protective mAbs. These molecules are candidate targets in rapid expulsion.

Trichinella spiralis: the effect of specific antibody on muscle larvae in the small intestines of weaned rats

Weaned rats were passively immunized with rat IgG2c monoclonal antibodies previously shown to protect infant rats against challenge with Trichinella spiralis. Although the antibodies did not protect rats against infection, the course of larval establishment in the intestine was altered in a way that has not been described previously. Specifically, larvae that invaded the epithelium were inhibited from migrating from intestinal tissue into saline during the standard recovery procedure. The inhibition was reversed at a time coincident with the first moult. Whole serum from infected rats had a similar effect. These results show that specific antibodies influence T. spiralis larvae in the intestinal epithelium, yet fail to effect their expulsion from adult rats.

Identification of potential antigenic targets for rapid expulsion of Trichinella spiralis

Rat monoclonal antibodies, which have been shown to mediate rapid expulsion of Trichinella spiralis in infant rats, were used in immunochemical analyses to identify the antigens targeted in protection. Protective antibodies bound to gp45, and to a series of related antigens, in the excretory-secretory products of muscle stage larvae. Non-protective antibodies did not bind gp45, but did bind the related species. The latter were shown to be present as aggregates (dimers and multimers) in excretory-secretory products. Protective antibodies bound to all four muscle larvae surface antigens (105, 97, 55, 51 kDa), while nonprotective antibodies bound to two species (97 and 51 kDa). In this way, the 97- and 51-kDa surface antigens were shown to be antigenically related to the non-gp45 species in excretory secretory material. Although protective properties of antibodies were found to be linked to gp45 and 105/55-kDa surface antigen binding, additional components in whole larval lysates were also bound by protective but not by nonprotective antibodies. Further definition of the target(s) of rapid expulsion and its related phenomena must await results of protection experiments designed to distinguish between the effects of antibody binding to surface and secreted antigens, including procedures employing purified, non-crossreactive antigens.

Diversity of the antibody responses produced in ponies and mice against the equine influenza A virus H7 haemagglutinin

A large panel of mouse monoclonal antibodies was produced and tested against field isolates of the equine H7N7 influenza A virus subtype. Only a limited degree of H7 haemagglutinin variation was detected. At least four antigenic sites were identified by selecting variant viruses in eggs. The limited variation in the field did not correlate with the frequency of variant viruses detected in eggs; this frequency was similar to those reported for other influenza viruses. We sought to determine whether the limited amount of variation could be correlated with an epitope-restricted antibody response in vaccinated horses. To this end, limiting dilution cultures were established with peripheral blood leukocytes from vaccinated ponies and the antibodies released into culture supernatants were assayed for binding to variant H7 viruses in ELISA. Three neutralizable antigenic sites mapped by mouse antibodies were also recognized by antibodies in pony limiting dilution culture supernatants, indicating that the equine antibody response against the influenza virus H7 haemagglutinin is diverse, and should be effective in selecting variant viruses.

Rapid expulsion of Trichinella spiralis in adult rats mediated by monoclonal antibodies of distinct IgG isotypes

The role of IgG in rapid expulsion of Trichinella spiralis in adult rats was analysed. In this experimental model, rats were first infected with an unrelated nematode Heligmosomoides polygyrus, then 5-14 days later, immune serum, its fractions, or IgG monoclonal antibody (mAb) was transferred. Rats were challenged with T. spiralis muscle larvae 24 hr after antibody transfer and intestinal worms counted at various times, up to 24 hr, after challenge. Provided rats were exposed to H. polygyrus first, immune serum, affinity chromatography-isolated immune IgE, IgE-depleted immune serum, or monoclonal antibodies of IgG1, IgG2a and IgG2c isotypes were all able to transfer rapid expulsion. Protection varied from 40 to greater than 90% larval T. spiralis rejection and was dose dependent, requiring, for IgG1, a minimum of 5 mg of transferred protein. Antibody specificity was predominantly against the dominant larval secreted/cuticular antigen TSL-1 for IgE and was exclusively so for the mAb. A comparison of quantitative differences in effective amounts of transferred antibody as well as the distinct priming requirements suggest that IgE functions through an intestinal mechanism that is different from that for IgG1 and IgG2c. Whether or not IgG2a functions homocytotropically, or as the other IgG has not been resolved. Since neither the T-helper (Th) cell transfer or the H. polygyrus form of intestinal priming confers protection by itself, these data suggest that rapid expulsion is predominantly an antibody-mediated process albeit with a required intestinal element. The results support earlier data in showing that two steps are required for rapid expulsion to be expressed and this is so for both IgE- and IgG-mediated mechanisms. Finally, the results show that IgG of various isotypes and IgE have a functional role in the expression of intestinal immunity.

The role of the antibody Fc region in rapid expulsion of Trichinella spiralis in suckling rats

When an IgG2c monoclonal antibody specific for Trichinella spiralis muscle stage larvae was cleaved with pepsin to yield F(ab')2 fragments, the latter retained their capacity to cause mucus entrapment and rapid expulsion of larvae from the intestines of suckling rats. When fed to pups, the F(ab')2 fragments of this antibody and the F(ab')2 fragments of a similarly prepared IgG2a antibody caused mucus entrapment of muscle larvae (ML), demonstrating that trapping is not dependent upon the Fc region of the antibody molecule. Despite the fact that these two antibodies had similar specificities and that their F(ab')2 fragments caused larval entrapment in mucus, F(ab')2 fragments of the IgG2a antibody failed to protect rat pups. Fragments of the IgG2c antibody caused rapid expulsion when injected into pups, but the distribution of larvae was dramatically different from when the fragments were delivered orally. These results indicate that entrapment of T. spiralis in mucus is not in itself the cause of the expulsion. The more likely possibility is that antibody impedes a function of Trichinella spiralis that is related to the capacity of the parasite to reside in its epithelial niche.

Intestinal mucus entrapment of Trichinella spiralis larvae induced by specific antibodies

Entrapment of muscle larvae (ML) occurred in vitro when antibodies specific for Trichinella spiralis were added directly to intestinal mucus from normal non-immunized rats or when mucus was collected from pups suckling a T. spiralis-infected dam. Normal rat serum immunoglobulins failed to promote mucus entrapment and complement did not appear to play a part in the entrapment process. Differences were not observed in the efficiency of entrapment of ML by mucus harvested from different regions of the small intestine. Employing a panel of monoclonal antibodies (mAb) specific for excretory-secretory antigen (ESA), we attempted to dissociate antibody-mediated protection from mucus entrapment. We assessed mucus entrapment and rapid expulsion by these mAb in vivo, and observed protection in the absence of significant, immediate mucus entrapment in two cases. In addition, we measured mucus entrapment of ML in two in vitro assays. One assay employed intestinal mucus harvested from pups suckling dams that had been injected i.v. with a mAb. Results confirmed those obtained in vivo and indicated that antibodies were present in the intestinal lumina of passively immunized pups. In the second in vitro assay, mAb were added individually to mucus from pups suckling non-immunized dams. Results from these assays suggested that certain antibody isotypes may be processed in vivo in ways that influence, either positively or negatively, their abilities to cause mucus entrapment.

The role of mucus in antibody-mediated rapid expulsion of Trichinella spiralis in suckling rats

Rat pups suckling dams parasitized by Trichinella spiralis express rapid expulsion, a protective response that is associated with the entrapment of infectious muscle larvae in intestinal mucus. Immunofluorescent studies revealed that antibodies were bound to the surfaces of the entrapped larvae. Mucus binding and rapid expulsion occurred in normal pups dosed with larvae coated with antibodies prepared from infected rat serum. Subsequent experiments revealed that entrapped larvae escaped from mucus after 2 hr in vitro incubation in saline. Escape correlated with the loss of the surface-bound antibodies, suggesting that mucus entrapment was reversible and dependent on antibody coating. Finally, when protective antibodies were injected 1, 2 or 6 hr after larvae were administered to pups, the parasites were forced to leave their epithelial niche and became enveloped in mucus. The above findings suggest that mucus trapping of T. spiralis larvae is dependent upon the coating of larvae by antibody, but that trapping is reversible, and is not in itself the pivotal event in rapid expulsion. The primary mechanism of rapid expulsion appears to be antibody-mediated inhibition of processes required for the parasite to maintain itself in the epithelium.

Production of an equine monoclonal antibody specific for the H7 hemagglutinin of equine influenza virus

Peripheral blood leucocytes from a pony previously exposed to equine influenza virus (H3, N8) and vaccinated with killed virus (H3, N8 and H7, N7 subtypes) were cultured in vitro with live A/equine/Prague/56 (H7, N7). On the sixth day of culture, cells were harvested and fused with mouse myeloma cells (X63-Ag8.653). From this fusion, one hemagglutinin specific, equine IgG monoclonal antibody secreting hybridoma was identified and cloned twice by limiting dilution. The antibody inhibited hemagglutination by nine H7 equine influenza virus isolates obtained over a 21-year period, but did not inhibit A/equine/Miami/63 (H3, N8), or A/PR/8/34 (H1, N1). The neutralizing titer of hybridoma induced, nude mouse ascitic fluid was 10(-4.5) when tested in eggs against 100 egg infective doses (EID50) A/equine/Prague/1/56. The hybridoma continued to synthesize antibody during more than 4 months in continuous culture.

Rapid expulsion of Trichinella spiralis in suckling rats: mediation by monoclonal antibodies

Pups born to rats immunized with the excretory/secretory antigens (ESA) of Trichinella spiralis L1 larvae expressed rapid expulsion when challenged orally. Rat monoclonal antibodies specific for ESA were produced and tested for their specificity in Western blots, binding to intact larvae and protective capacity in suckling rats. Eight antibodies had apparently identical specificity in Western blots, each recognizing a polypeptide family that included three molecular weight species sized at 41,000-50,000 MW. These polypeptides formed a series of higher molecular weight aggregates that were also bound by the monoclonal antibodies. Four of eight antibodies were protective when serially transferred to suckling pups. Each protective antibody was able to bind to intact larvae. Antibodies of two subclasses, IgG1 and IgG2c, were strongly protective, delivering to pups the capacity to expel as much as 94% of the challenge dose.

Characterization of the immune mediator of rapid expulsion of Trichinella spiralis in suckling rats

In order to identify and characterize the mediator(s) of rapid expulsion, infant rats were passively immunized against oral challenge with 200 infectious Trichinella spiralis muscle larvae by oral or intraperitoneal (i.p.) administration of secretions or sera from infected rats. Milk whey from infected dams provided a modest level of protection when fed to pups. Immunoglobulins from T. spiralis-infected rat serum protected suckling pups when injected intravenously (i.v.) into lactating dams 2 days prior to pup challenge. Intraperitoneal injection of pups with serum immunoglobulins also enabled them to express rapid expulsion. The protective component of serum was precipitated with 40% (NH4)2SO4 and was not affected by heating to 56 degrees, although antibodies mediating passive cutaneous anaphylaxis were inactivated by both treatments. Oral transfer of biliary immunoglobulins collected from infected rats at various times during a primary infection provided no protection to pups. However, serum immunoglobulins from rats infected for 42 days or longer transferred rapid expulsion to pups. Absorption of protective serum immunoglobulins with subclass-specific reagents revealed that IgG1 played a significant role in protection.

Characterization of the equine influenza virus H3 with monoclonal antibodies

Mouse monoclonal antibodies specific for the hemagglutinin of the prototype equine-2 virus, A/equine/Miami/1/63 (H3, N8) demonstrated two related antigenic sites on the H3. One of the sites was detected on 14 H3 viruses isolated over a 22 year period (1963-1985). Variant viruses were selected with these antibodies at frequencies similar to those described for H3 hemagglutinins from human isolates.

Life-phase specific induction and expression of rapid expulsion in rats suckling Trichinella spiralis-infected dams

Rat dams infected with 1000 Trichinella spiralis muscle larvae, 4 weeks prior to breeding, provided their suckling offspring with immunity to challenge with 200 muscle larvae at 2 weeks of age. The immunity was expressed in the elimination of 75-99% of the challenge dose within 24 hr. The intestinal worm burden did not decline significantly after the initial expulsion. Infected dams continued to protect their offspring during three breeding cycles, for as long as 26 weeks after infection. Immunity was conferred upon pups by dams that had been selectively immunized with the parenteral phase of the parasite's life cycle. Immunization with a drug-terminated enteral infection was ineffective as was enteral immunization followed by the parenteral phase. Further analysis revealed that rapid expulsion by pups was dependent on the number of mature muscle larvae recovered from dams immunized with NBL. By comparison, the expulsive capacity of the same dams was not improved by increasing the numbers of NBL within the range tested.

Appearance of immunoglobulin classes and complement (C3) during Corynebacterium renale-induced experimental pyelonephritis in the rat

The local appearance of various immunoglobulin (Ig) isotypes in the urinary tract during ascending pyelonephritis was studied in rats experimentally infected with Corynebacterium renale. The indirect fluorescent antibody assay was used to detect IgG, IgM, IgA, IgE, and C3 on C renale present in the urine of the experimental animals. Corynebacterium renale coated with IgM and IgG antibodies was found beginning on the 4th day after induced infection, with IgG being the more abundant isotype. Coating with IgA occurred as early as the 4th day, but was less dense than coating with IgG. The presence of C3 on C renale was concurrent with IgM and IgG coating. A significant quantity of IgE could not be identified on antibody-coated C renale. Thus, IgG is the major component of the humoral immune response in this model of ascending pyelonephritis. The IgM early during infection and IgA later during infection seem not to be a major component of the immune response in this model.

Rapid expulsion of Trichinella spiralis in suckling rats

Orally administered Trichinella spiralis muscle larvae were rapidly expelled by rat pups suckling an immune dam. The immunity was delivered in the milk; substantial resistance was conferred on normal rat pups suckled for only 24 hours by a Trichinella-immune foster mother. The pups were protected by oral or systemic administration of specific serum antibodies. When infused into a normal lactating dam, these antibodies accumulated in the serum of her suckling pups.

Identification of bluetongue virus type 17 genome segments coding for polypeptides associated with virus neutralization and intergroup reactivity

Double-stranded (ds) RNA was isolated from either partially purified bluetongue virus (BTV) type 17 or BTV-17 infected cells. The RNA was denatured with either methylmercury hydroxide or dimethyl sulfoxide and translated in a reticulocyte cell-free system. The translation products were found to be similar to BTV-17 specific polypeptides in infected cells when analyzed by polyacrylamide gel electrophoresis and immunoprecipitation with BTV-17 specific polyclonal mouse ascitic fluid. The 10 dsRNA BTV-17 genome segments were resolved by preparative gel electrophoresis and the coding assignment of each segment was determined by translation in a cell-free system. Immunoprecipitation of VP3 from infected cell lysates by a type-specific neutralizing monoclonal antibody identified this polypeptide, which is coded for by genome segment 2, as being involved in virus neutralization. Immunoprecipitation of in vitro translation products directed by total BTV-17 RNA with a monoclonal antibody that reacts with all the serotypes of BTV and some other orbiviruses and precipitates VP7 directly demonstrated that gene segment 8 codes for this intergroup-specific polypeptide.

Monoclonal antibody analysis of serotype-restricted and unrestricted bluetongue viral antigenic determinants

Twenty-one monoclonal antibodies that react with bluetongue virus (BTV) and have restricted or unrestricted serotype specificities were identified in culture supernatants of hybridomas derived from lymphocytes of mice immunized with BTV serotype 17. Hybridomas were screened and antibody specificities characterized in a solid-phase radioimmunoassay and by immunoprecipitation with radiolabeled, BTV 17-infected cell lysates. Three general serotype specificities were demonstrated by 13 antibodies that precipitated structural viral protein 9 (VP 9). One antibody precipitated VP 7, a 48,000 dalton nonstructural protein, and reacted in radioimmunoassay with 20 BTV serotypes and Epizootic Hemorrhagic Disease of Deer Virus serotype 1 (EHDV 1), EHDV 2, and Ibaraki virus, but not with uninfected cells. One serotype-specific antibody neutralized infectivity, inhibited hemagglutination by BTV 17, and precipitated VP 2 and VP 3. A second antibody, with restricted serotype specificity, precipitated VP 2 and VP 8. These results confirm those of others (Huismans and Erasmus, Onderstepoort J. Vet. Res. 48, 51-58, 1981) that BTV serotype-specific and neutralizing epitopes are associated with VP 2.

Heterogeneity of neutralization-related epitopes within a bluetongue virus serotype

Twenty-four monoclonal antibodies raised against a 1962 Wyoming isolate of blue-tongue virus serotype 17 (BTV 17) were tested against 20 other field isolates of this serotype in a solid-phase radioimmunoassay (RIA), neutralization, and mouse passive protection tests. Of the 21 antibodies that bound in RIA to acetone-fixed BTV-infected cells, 18 bound to cells infected with any of the BTV 17 isolates and 3 detected minor antigenic differences in two isolates. The remaining 3 antibodies, that bound in RIA only to unfixed virus-infected cells detected additional differences. Of the 3 antibodies binding to unfixed virus-infected cells one bound to all but 2 isolates. A second antibody, 6C3A.2, bound only to the Wyoming isolate and passively protected mice against this isolate. The third antibody, 6C2A.4.2, bound to the Wyoming isolate and to 8 isolates from the mid-South U. S., but not to 12 isolates from California. Antibody 6C2A.4.2 neutralized the Wyoming and mid-South isolates to which it bound and passively protected mice against the Wyoming isolate but provided little or no protection against 4 California isolates tested. Polyclonal serum from mice immunized against Wyoming BTV 17 bound in RIA to all BTV 17 isolates and neutralized all isolates. Thus, three neutralization-related antigenic determinants were disclosed, one (perhaps a set) recognized by immune sera on all BTV 17 isolates, a second recognized by antibody 6C2A.4.2 on the Wyoming and 8 mid-South isolates, and a third recognized by antibody 6C3A.2 only on the Wyoming isolate. These differences may be important in selection of virus strains for vaccine development.

Passive protection of mice and sheep against bluetongue virus by a neutralizing monoclonal antibody

A murine hybridoma antibody, 6C2A.4.2, previously characterized as an immunoglobulin G class 2a that binds in radioimmunoassay to bluetongue virus serotype 17 (BTV-17) but not the other 19 BTV serotypes, neutralizes BTV-17, inhibits hemagglutination with BTV-17, and precipitates viral polypeptides 2 and 3 from BTV-17-infected cells, was produced as an ascites in the peritoneal cavities of hybridoma-inoculated mice. This ascitic fluid, but not those containing other, non-neutralizing anti-BTV-17 antibodies of the same isotype, provided serotype-specific passive protection against BTV-17-induced death of neonatal mice. Antibody 6C2A.4.2-containing ascitic fluid was injected intravenously into sheep that were later inoculated with BTV-17. These sheep remained free of clinical signs, did not develop viremia or detectable levels of antibodies reactive in the immunodiffusion test used for routine BTV diagnosis in the United States, and developed only low levels of neutralizing antibodies. Control animals became viremic and developed immunodiffusion test reactions and high levels of neutralizing antibodies during recovery, and two of three had lesions and fevers. These results provide evidence that antibodies directed against a single epitope on BTV-17 can prevent bluetongue disease.

Scanning electron microscopy of experimentally induced pyelonephritis in the rat

Scanning electron microscopy was used to observe epithelial and inflammatory changes in kidneys of rats during Corynebacterium renale-induced experimental ascending pyelonephritis. Bacteria were not observed adhering to pelvic epithelium, although there was evidence of cell sloughing. Bacteria was observed in the interstitium of the renal medulla. Bacteria, when present in the tubular lumen, were associated with discontinuities in cell membranes. Phagocytic cells appeared in the interstitium and phagocytosis was evident in the renal medulla.

Antibody formation in Corynebacterium renale-induced experimental pyelonephritis in the rat

The immune defense system of the kidney was studied by inducing ascending pyelonephritis in rats with Corynebacterium renale. With the fluorescent antibody technique, C renale organisms were observed in the renal pelvis, but were not coated with antibody until they reached the medulla. Histopathologic evaluation of renal tissues collected serially after inoculation confirmed the presence of infection in the medulla when antibody coating occurred. Serum anti-C renale antibody concentrations increased after antibody-coated bacteria appeared in the urine and kidney. Free anti-C renale antibody was not detected in urine from infected rats, using the microagglutination assay. Antibody coating appears to occur only after C renale organisms invade the medulla during ascending pyelonephritis.