Trichinella spiralis and Strongyloides ratti: immune interaction in adult rats.

The consequences of prior and concurrent infection with two species of nematodes were studied in rats. Primary infection with Strongyloides ratti adversely affected the development of a secondary Trichinella spiralis infection. Both immediate and delayed challenge with T. spiralis, following the expulsion of the previous S. ratti infection, reduced the percentage of worm recovery of the former as well as their fecundities and lengths. It is suggested that nonspecific inflammation produced by one species, during the peak period of worm expulsion, was not responsible for the accelerated rate of expulsion of the other; instead a direct, specific cross-immunity was probably operative affecting the survival of the challenge species. The response elicited by previous experience of the intestinal phase was reciprocal, but there was evidence of an enhancing effect by the muscle larval stages of T. spiralis on S. ratti. Rats concurrently infected with both species expelled S. ratti more rapidly than T. spiralis. Possible mechanisms underlying the interaction between the two species are suggested and discussed.     

Mucosal Immune Responses of Mice Experimentally Infected with Pygidiopsis summa (Trematoda: Heterophyidae)

Mucosal immune responses against Pygidiopsis summa (Trematoda: Heterophyidae) infection were studied in ICR mice. Experimental groups consisted of group 1 (uninfected controls), group 2 (infection with 200 metacercariae), and group 3 (immunosuppression with Depo-Medrol and infection with 200 metacercariae). Worms were recovered in the small intestine at days 1, 3, 5, and 7 post-infection (PI). Intestinal intraepithelial lymphocytes (IEL), mast cells, and goblet cells were counted in intestinal tissue sections stained with Giemsa, astra-blue, and periodic acid-Schiff, respectively. Mucosal IgA levels were measured by ELISA. Expulsion of P. summa from the mouse intestine began to occur from days 3-5 PI which sustained until day 7 PI. The worm expulsion was positively correlated with proliferation of IEL, mast cells, goblet cells, and increase of IgA, although in the case of mast cells significant increase was seen only at day 7 PI. Immunosuppression suppressed all these immune effectors and inhibited worm reduction in the intestine until day 7 PI. The results suggested that various immune effectors which include IEL, goblet cells, mast cells, and IgA play roles in regulating the intestinal mucosal immunity of ICR mice against P. summa infection.     

Trichuris muris: effect of concurrent infections with rodent piroplasms on immune expulsion from mice.

Mice concurrently infected with the rodent piroplasms Babesia hylomysci or B. microti during a primary infection with the nematode Trichuris muris showed marked immunodepression, and the normal immune expulsion of the nematode was delayed. Immunodepression was most severe when the Babesia infections reached peak parasitaemia during the preexpulsion phase of the worm infection. Decline in parasitaemia to subpatent levels was associated with a reappearance of the immune response and expulsion of the worm. Babesia infections had little effect upon the expulsion of challenge infections of T. muris from mice previously immunized against the worm. Acute Babesia infections were found to exert a profound immunodepressive effect upon the agglutinating antibody response of mice to sheep red blood cells.     

Trichinella spiralis: mediation of the intestinal component of protective immunity in the rat by multiple, phase-specific, antiparasitic responses.

Rats infected orally with Trichinella spiralis developed an immunity that was induced by and expressed against separate phases of the parasite's enteral life cycle. Infectious muscle larvae generated an immune response (rapid expulsion) that was directed against the very early intestinal infection and resulted in the expulsion of worms within 24 hr. This response eliminated more than 95% of worms in an oral challenge inoculum. Developing larvae (preadults) also induced an immune response that was expressed against adult worms. The effect on adults was dependent upon continuous exposure of worms to the immune environment throughout their enteral larval development. Immunity induced by preadult T. spiralis was not expressed against adult worms transferred from nonimmune rats. While adult worms were resistant to the immunity engendered by preadults they induced an efficient immunity that was autospecific. Both “preadult” and “adult” immunities were expressed in depression of worm fecundity as well as in the expulsion of adults from the gut. However, the two reactions differed in respect to their kinetics and their efficiency against various worm burdens. Preadult immunity was directed mainly against fecundity whereas adult immunity favored worm expulsion. All responses (rapid expulsion, preadult and adult immunity, and antifecundity) acted synergistically to produce sterile immunity against challenge infections of up to 5000 muscle larvae. These findings indicate that the host protective response to T. spiralis is a complex, multifactorial process that operates sequentially and synergistically to protect the host against reinfection.     

Strongyloides ratti: Mast cell and goblet cell responses in the small intestine of infected rats

Kinetics of intestinal mast cells and goblet cells were examined in relation to worm localization at various sites in the small intestine of rats infected with 3000 filariform (stage 3) larvae of Strongyloides ratti. The most marked intestinal mastocytosis was observed on Day 20 at the anterior site of the small intestine where the majority of the worms had concentrated. The number of mast cells in the posterior small intestine increased in parallel with the posterior shift of parasites at the later stage of the infection. In contrast to the intestinal mast cell response, the number of goblet cells was not significantly affected by the infection. These results strongly suggest that intestinal mastocytosis is closely related to the presence of the worms and that mast cells may play an important role for the expulsion of S. ratti.     

The response of the small intestine of the protein-deficient rat to infection with Nippostrongylus brasiliensis

The intestinal response of the protein-deficient Wistar rat was examined after primary infection with 1500 larvae of Nippostrongylus brasiliensis. Protein-deficient animals failed to expel N. brasiliensis after 15 days at a time when nutritionally normal animals had expelled more than 99% of the worm burden. Morphology of the small intestine of protein-deficient animals before infection showed small villi and crypt hypoplasia, followed after infection by sustained crypt hyperplasia and increased mitotic index of crypts. Protein deficiency was associated with fewer mucosal mast cells, goblet cells and intraepithelial lymphocytes. There was an impaired response of mucosal mast cells and goblet cells to infection. This could explain the deficiency of worm expulsion in these protein-deficient animals.     

Trypanosoma musculi and Trichinella spirails: Concomitant infections and selection for resistance genotypes in mice

Trypanosoma musculi infections were given to mice of different strains before, at the same time, and after an infection with 400 Trichinella spiralis. Examined parameters of the host response to T. spiralis were worm rejection, antifecundity responses, development of immunological memory, and muscle larvae burden. After dual infection, each mouse strain showed characteristic effects on resistance to T. spiralis. This was due to a dynamic interaction between the genes controlling rejection of T. spiralis and those influencing T. musculi growth. C3H mice develop high trypanosome parasitemias. This impairs worm expulsion and the development of memory to T. spiralis when Trypanosoma infections take place on the same day or 7 days before. The C57B1/6 mouse develops low parasitemias and T. musculi infections on the same day, or 7 days before T. spiralis, delaying worm rejection only slightly despite the overall weak capacity of B6 mice to expel worms. NFR-strain mice are strong responders to T. spiralis and also develop low parasitemias. Trypanosome infections on the same day, or after T. spiralis, produce a delay in worm rejection; the former is comparable to C3H mice. However, NFR mice alone showed enhanced rejection of worm when T. musculi infections preceded T. spiralis by 7 days. An unusual feature of C3H mice was that T. musculi infections 7 days before T. spiralis increased antifecundity responses at the same time that worm expulsion was inhibited. Trypanosome infections can therefore modulate distinct antihelminth immune responses in different directions simultaneously. The different outcomes of dual infections compared with single infections provides another selective mechanism by which genetic polymorphisms can be established and maintained in the vertebrate host.     

The effect of Plasmodium berghei and Trypanosoma brucei infections on the immune expulsion of the nematode Trichuris muris from mice

The effects of concurrent P. berghei or T. brucei infections on the immune expulsion of primary and challenge infections of T. muris from CFLP strain mice have been examined. CFLP mice usually expel the nematode 18–21 days after a primary infection and within 4–6 days after a challenge infection. Both acute malaria and trypanosome infections initiated at the same time as the T. muris infection suppressed worm expulsion; when the protozoal infections were started 7 days after the T. muris infection worm expulsion was suppressed in a proportion of the mice. Acute trypanosome and malaria infections delayed the expulsion of a challenge infection from immune mice, but in the case of P. berghei the delay was short-lived.     

Immunity to primary and challenge infections of Trichinella spiralis in mice: a re-examination of conventional parameters.

In young (6- to 8-week-old) NIH strain inbred mice expulsion of a primary infection of Trichinella spiralis began on day 8 and was virtually complete by day 11-5. In older mice expulsion occurred 1 or 2 days earlier. Experience of a primary infection elicited strong immunity to challenge, whether the challenge was given immediately after worm expulsion (day 14) or delayed (day 42). Challenge infections were expelled rapidly the majority of worms being lost during the first day. Immunity to challenge was elicited by low-level primary infections and was effective against large ventionally accepted parameters of immunity to T. spiralis in mice which, it is considered, are applicable only to mice with a genetically determined low-level of responsiveness to the parasite.     

Nippostrongylus brasiliensis: Increase of sialomucins reacting with anti-mucin monoclonal antibody HCM31 in rat small intestinal mucosa with primary infection and reinfection

Infections with the parasitic helminth, Nippostrongylus brasiliensis, cause changes in rat small intestinal goblet cell mucin, particularly in the peripheral sugar residues of oligosaccharide. These changes may correlate with expulsion. In this study, we examined changes in mucin oligosaccharides caused by primary infection and reinfection with N. brasiliensis, using two monoclonal antibodies, HCM31 and PGM34, that react with sialomucin and sulfomucin, respectively. Enzyme-linked immunosorbent assay of jejunal mucins showed that the relative reactivity of mucins with HCM31, but not PGM34, increased up to 16 days after primary infection and 6 days after reinfection, the times when the worms were expelled from the rats. Immunohistochemical studies confirmed that goblet cells stained with HCM31 greatly increased at the time of worm expulsion. These results indicate that the marked increase observed in HCM31-reactive sialomucins may be related to expulsion of the worms.     

STAT6 Expression and IL-13 Production in Association with Goblet Cell Hyperplasia and Worm Expulsion of Gymnophalloides seoi from C57BL/6 Mice

In intestinal helminth infections, Th2 immune respones are generally associated with mucin secretion for worm expulsion from the host intestine. In particular, IL-4 and IL-13 are the important cytokines related with intestinal mucus production via STAT6 signalling in nematode infections. However, this perspective has never been studied in Gymnophalloides seoi infection. The present study aimed to observe the STAT6 signalling and cytokine responses in C57BL/6 mice, a mouse strain resistant to infection with this trematode. The results showed that worm expulsion occurred actively during days 1-2 post-infection (PI), when goblet cells began to proliferate in the small intestine. The STAT6 gene expression in the mouse spleen became remarkable from day 2 PI. Moreover, G. seoi infection induced a significant increase of IL-13 from day 4 PI in the spleen of infected mice. Our results suggested that goblet cell hyperplasia and worm expulsion in G. seoi-infected mice should be induced by STAT6 signalling, in which IL-13 may be involved as a dominant triggering cytokine.     

Trichinella spiralis: expression of rapid expulsion in rats exposed to an abbreviated enteral infection.

Rats infected with Trichinella spiralis for the first week of the enteral infectious cycle displayed a strong rapid expulsion reaction during a challenge infection. The response was induced with equal facility in animals given low or high immunizing doses of infectious larvae (500 to 5000 larvae). Large challenge infections resulted in a 10–15% reduction in the efficiency of rejection as assessed 24 hr after challenge. Rats became primed to express rapid expulsion within the first week of primary infection whether the infection remained patent or not. However, maximum effectiveness was not realized until the second week after the initial infection. Once induced, the capacity to express rapid expulsion persisted for 6 weeks after the primary infection. Immunized hosts were capable of resisting two challenge infections spaced by periods of from 12 to 72 hr. This finding suggests that a mediator is not consumed by the initial response.     

Rapid and specific alterations of goblet cell mucin in rat airway and small intestine associated with resistance against Nippostrongylus brasiliensis reinfection

The intestinal parasitic nematode Nippostrongylus brasiliensis is expelled rapidly from the rat in reinfection challenge compared with that of the primary infection owing to the host defense mechanisms raised against the pre-intestinal- and intestinal-stage larvae. We examined the relationship between the mucin alterations in airway and jejunal mucosae and the worm expulsion after third-stage larva reinfection. When rats had been inoculated with fourth-stage larvae and immunized with only the intestinal-stage worms for more than 8 days, the challenge larvae were expelled during the intestinal stage along with a rapid increase of the specific sialomucin in jejunal mucosa, without any effect on the bronchial mucus. When rats had been infected with third-stage larvae and immunized with only the pre-intestinal stage larvae by killing with antihelminthic, the challenge larvae were rejected during the pre-intestinal stage along with marked goblet cell hyperplasia and Muc5AC mucin hyperproduction on the bronchial mucosa, but not as a result of jejunal mucin alteration. Taking these finding together, immunization with pre-intestinal- and intestinal-stage worms independently increases the airway and intestinal goblet cell mucins, respectively, and in both cases, the mucin alterations may contribute to rapid worm expulsion upon reinfection.     

Trichinella spiralis: Delayed rejection in mice concurrently infected with Nematospiroides dubius

The immune response of mice to the nematode Trichinella spiral's was markedly altered when the infection was superimposed upon an existing infection with Nematospiroides dubius. The expulsion of a primary infection of T. spiralis was delayed in such mice, and the worms persisted for at least 4 weeks longer than they did in control mice. The degree to which expulsion was suppressed was related to the number of N. dubius present. It would appear that both adult and larval stages of N. dubius can exert a suppressive effect, since the expulsion of T. spiralis was affected within days of a super-imposed (i.e., larval) N. dubius infection. When adult N. dubius were removed from mice 4 days before infection with T. spiralis, the mice expelled the latter parasite within the normal time, indicating that recovery from the suppressive effects of concurrent infection occurred rapidly. Concurrent infection with N. dubius appeared to affect both the afferent and efferent arms of the immune response to T. spiralis, since sensitization by, and memory of, prior infection were impaired and the expression of acquired immunity was inferior to that of controls.     

Immunity to intestinal parasites: role of mast cells and goblet cells

Nippostrongylus brasiliensis infection of rats and mice is a model for studying immunity at mucosal surfaces. Adult worms are spontaneously expelled from the intestine at the end of the second week of infection. Expulsion from the jejunum requires the presence of immune T lymphocytes and IgG antibodies. Mucosal mast cells (MMCs) are a prominent part of the jejunal inflammatory response. They are derived from a hematopoietic stem cell, possibly the same precursor as basophils. Their differentiation is not absolutely T dependent but their accumulation at the site of infection is. The possible involvement of IgE antibodies and intestinal MMCs through a "leak lesion" is still uncertain. Increased mucus secretion from epithelial goblet cells is also a prominent feature of the inflammatory reaction at the site of infection. Goblet cell numbers increase two to four times at the onset of worm expulsion; this increase is regulated by T lymphocytes and possibly immune serum. The mechanism of mucus secretion in these infections is not clear; it may be a response to mast cell mediators. Together with antiworm antibodies, intestinal mucus may trap worms and prevent them from surviving in the intervillous spaces of the jejunum. Thus, expulsion of this intestinal parasite may occur through a nonspecific process that is induced by specific immune mechanisms.     

Trichinella spiralis: Characterization and strain distribution of rapid expulsion in inbred mice

Appropriately immunized mice display a response that is biologically equivalent to rat rapid expulsion. Only two inbred strains ($\text{NFR}\text{N}\text{and}\text{NFS}\text{N}$ derived from NIH Swiss mice) have been shown to respond in this manner. Mice of the $\text{Balb}\text{c}$, CBA, $\text{A}\text{He}$, C₃H, SJL, or C₅₇Bl strains are “nonresponders” which require approximately twice as much intestinal exposure (in days) to Trichinella spiralis to elicit a response half as effective. Genetically, the responder is dominant, autosomal, and does not appear to be linked to the MHC. The characteristics of mouse and rat rapid expulsion of T. spiralis are not identical but share these features: initial rejection within 24 hr of challenge; a rejection efficiency >90%, from 1 to 5 weeks after the primary; induction of response does not require exposure to the complete infection; rapid expulsion is immunologically specific for preadults; adult worms are resistant. While a genetic basis for responsiveness exists in mice there is, as yet, no evidence for genetic control in rats. In both mice and rats, rapid expulsion is distinguished from the intestinal hyperreactivity associated with rejection of the primary infection by the kinetics and amplitude of the rejection of transplanted adult worms.     

Nippostrongylus brasiliensis: intestinal goblet-cell response in adoptively immunized rats.

Goblet-cell differentiation was studied in the intestinal epithelium of rats infected with the nematode Nippostrongylus brasiliensis. An increase in the proportion of goblet cells occurred at the time of worm expulsion in rats infected with 1000 or 4000 third stage larvae. Adoptive immunization of infected rats with immune-thoracic duct lymphocytes (TDL) induced extensive goblet-cell differentiation whereas the transfer of immune-TDL into normal rats had no effect. The extent of goblet-cell differentiation in adoptively immunized infected rats was proportional to the number of cells transferred. A goblet-cell response also occurred in adoptively immunized rats harboring implanted “normal” and “damaged” worms but recipients of normal worms which were not given cells were unable either to expel their worm burden or to induce a goblet-cell response. Experiments in which the parasites were expelled with an anthelmintic drug suggested that the goblet-cell increase was not simply a repair process associated with the expulsion of the parasites. In all situations where immune expulsion of the parasites occurred, there was a concomitant rise in the proportion of goblet cells. These experiments suggest that thoracic duct lymphocytes either directly or indirectly regulate the differentiation of intestinal goblet cells.     

Kinetics of primary and secondary infections with Strongyloides ratti in mice

Dawkins H. J. S. and Grove D. I. 1981 Kinetics of primary and secondary infections with Strongyloides ratti in mice. International journal for Parasitology11: 89–96. The kinetics of infection with S. ratti were quantitated in normal and previously exposed C57B1 /6 mice. In primary infections, larvae penetrated the skin rapidly and were seen in peak numbers 12 h after infection. By 24 h after infection, larval numbers had declined appreciably and there was a slow decrease in numbers thereafter. Larvae were first observed in the lungs at 24 h and maximal recovery occurred at 48 h. It is thought that larval migration through the lungs is rapid. Worms were first seen in the intestines two days after infection. Maximum numbers were seen on the fifth day and worm expulsion was complete by day 10. Two moults took place in the small intestine during days 3 and 4 after infection. Rhabditiform larvae were first noted on the fourth day after infection. Mice exposed to S. ratti four weeks previously had significantly less larvae in the skin 4 and 12 h after infection but by 24 h there was no difference when compared with mice with primary infections. Peak recovery of larvae from the lungs occurred 24 h after infection; significantly less larvae were recovered on days 2 and 3 when compared with normal mice. There was a marked reduction in the adult worm burden in the gut; the number of worms recovered was less than one fifth of that seen in primary infections. Those worms which did mature were less fecund and were expelled from the intestines within 7 days of infection. It is suggested that in previously exposed animals, the migration of larvae from the skin is hastened, many of these larvae are destroyed in the lungs and that expulsion of worms which do mature in the intestines is accelerated.     

Increased Intestinal Epithelial Cell Turnover and Intestinal Motility in Gymnophalloides seoi-Infected C57BL/6 Mice

The changing patterns of goblet cell hyperplasia, intestinal epithelial cell turnover, and intestinal motility were studied in ICR and C57BL/6 mice infected with Gymnophalloides seoi (Digenea: Gymnophallidae). Whereas ICR mice retained G. seoi worms until day 7 post-infection (PI), C57BL/6 mice showed a rapid worm expulsion within day 3 PI. Immunosuppression with Depo-Medrol significantly delayed the worm expulsion in C57BL/6 mice. Goblet cell counts were increased in both strains of mice, peaking at day 1 PI in C57BL/6 mice and slowly increasing until day 7 PI in ICR mice. In C57BL/6 mice infected with G. seoi, newly proliferating intestinal epithelial cells were remarkably increased in the crypt, and the increase was the highest at day 1 PI. However, in ICR mice, newly proliferating intestinal epithelial cells increased slowly from day 1 to day 7 PI. Intestinal motility was increased in G. seoi-infected mice, and its chronological pattern was highly correlated with the worm load in both strains of mice. Meanwhile, immunosuppression of C57BL/6 mice abrogated the goblet cell proliferation, reduced the epithelial cell proliferation, and suppressed the intestinal motility. Goblet cell hyperplasia, increased intestinal epithelial cell turnover, and increased intestinal motility should be important mucosal defense mechanisms in G. seoi-infected C57BL/6 mice.     

Intestinal immunity suppresses carrying capacity of rats for the model tapeworm, Hymenolepis diminuta

Hymenolepis diminuta is a parasitic tapeworm of the rat small intestine and is recognized as a useful model for the analysis of cestode-host interactions. In this study, we analyzed factors affecting the biomass of the tapeworm through use of rat strains carrying genetic mutations, namely X-linked severe combined immunodeficiency (xscid; T, B and NK cells deficiency), nude (rnu; T cell deficiency), and mast cell deficient rats. The worm biomass of F344-xscid rats after infection with 5 cysticercoids was much larger than control F344 rats from 3 to 8?weeks. The biomass of F344-rnu rats was also larger than the controls, but was intermediate between F344-xscid and control rats. These observations demonstrated that host immunity can control the maximal tapeworm biomass, i.e., carrying capacity, of the rat small intestine. Both T cell and other immune cells (B and NK cells) have roles in determining the carrying capacity of tapeworms. Total worm biomass and worm numbers in mast cell deficient rats (WsRC-Ws/Ws) were not significantly different from control WsRC-+/+ rats after 3 and 6?weeks of primary infection. Mast cell deficient rats displayed reinfection resistance for worm biomass but not worm expulsion. These findings suggest that the mast cell has a role for controlling the biomass of this tapeworm in reinfection alone, but does not affect the rate of worm expulsion. Overall, our findings indicate that the mast cell is not a major effector cell for the control of the carrying capacity of tapeworms. The identity of the major effector cell remains unknown.