Assessing immunocompetence in red palm weevil adult and immature stages in response to bacterial challenge and entomopathogenic nematode infection

Parasites and pathogens can follow different patterns of infection depending on the host developmental stage or sex. In fact, immune function is energetically costly for hosts and trade‐offs exist between immune defenses and life history traits as growth, development and reproduction and organisms should thus optimize immune defense through their life cycle according to their developmental stage. Identifying the most susceptible target and the most virulent pathogen is particularly important in the case of insect pests, in order to develop effective control strategies targeting the most vulnerable individuals with the most effective control agent. Here, we carried out laboratory tests to identify the most susceptible target of infection by infecting different stages of the red palm weevil Rhynchophorus ferrugineus (larvae, pupae, male, and female adults) with both a generic pathogen, antibiotic‐resistant Gram‐negative bacteria Escherichia coli XL1‐Blue, and two specific strains of entomopathogenic nematodes (EPNs), Steinernema carpocapsae ItS‐CAO1 and Heterorhabditis bacteriophora ItH‐LU1. By evaluating bacterial clearance, host mortality and parasite progeny release, we demonstrate that larvae are more resistant than adults to bacterial challenge and they release less EPNs progeny after infection despite a higher mortality compared to adults. Considering the two EPN strains, S. carpocapsae was more virulent than H. bacteriophora both in terms of host mortality and more abundant progeny released by hosts after death. The outcomes attained with unspecific and specific pathogens provide useful information for a more efficient and sustainable management of this invasive pest.     

Lumen phase specific cross immunity between Hymenolepis microstoma and H. nana in mice

, and 1988. Lumen phase specific cross immunity between Hymenolepis microstoma and H. nana in mice. International Journal for Parasitology 18: 1019–1027. When mice inoculated with five cysticercoids of Hymenolepis microstoma were challenged with H. nana, they showed strong resistance to challenges with both eggs and cysticercoids of H. nana from day 20. The immunity became complete from day 30 onward: no tissue cysticercoids or lumenal adults of H. nana were established in these mice. However, when mice were challenged with H. nana 10 or 20 days after 10-day old immature H. microstoma were removed by an anthelmintic, the immunity evoked was directed exclusively against the lumenal phase of the cysticercoid challenge but not the tissue cysticercoids of the egg challenge. When mice experienced the prepatent infection with H. microstoma twice, the immunity evoked was also against the lumenal phase of the egg challenge: the oncospheres developed into tissue cysticercoids but thereafter completely failed to develop into lumenal adult tapeworms. Infection with a single cysticercoid of H. microstoma was shown to be sufficient to evoke immunity against H. nana cysticercoid infections in two strains of mice. Sera from mice which experienced a patent infection with H. microstoma revealed that IgG, IgA, IgM isotypes reacted against oncospheres and cysticercoids of both species, while sera from mice which experienced two prepatent infections reacted with cysticercoids only. Sera from H. microstoma infected mice resistant to H. nana caused precipitations on 4-day-old H. nana in vitro. A correlation exists between the presence of stage specific antibodies and resistance to the different stages.     

Circulating immunoglobulins and complement in mice with Hymenolepis nana infection

Changes in the circulating immunoglobulins and complement in ddY mice were assayed at various times after immunizing and challenge infections with Hymenolepis nana eggs. The levels of IgG1 and IgG2a consistently increased during 3–4 weeks after immunizing infection. The increase of these immunoglobulins after challenge infection was quicker and more intense than that following immunization. It was not possible to correlate increased levels of IgG1 and IgG2a with the onset of destruction of challenge larvae in immunized mice. IgM concentrations increased slightly during 4 days after immunization but challenge infection did not further increase IgM levels. IgA and IgG2b levels showed no significant change during the course of the infection. Serum C3 levels showed no discernible change after either immunizing or challenge infections. An attempt to specifically suppress the acquisition of resistance by administration of the complement-depleting agent, cobra venom factor (CoF), before immunization failed and depletion of complement activity with CoF that was administered just before challenge infection also failed to affect resistance. These results suggest that complement has no critical role in either induction of the response nor in the anamnestic response to H. nana infection in mice.     

Nematospiroides dubius: genetic control of immunity to infections of mice

Inbred strains of mice differ in their susceptibility and resistance to challenge infections with Nematospiroides dubius. In our studies, F1 hybrid mice from resistant SJL and susceptible CBA parents were resistant to N. dubius challenge infections. Only 22% of backcrosses to SJL were susceptible while backcrosses to CBA had a wide range of susceptibility. Male mice were more susceptible than female mice. In another experiment, inbred strains of mice were compared in their ability to resist N. dubius challenge infection: SJL and A.SW (H-2s) mice became resistant after one immunizing infection, A, A/He (both H-2a), as well as BALB/c and DBA/2 (both H-2d) mice became resistant after two immunizing infections, while C57BL/6 (H-2b), C3H/He, CBA, and AKR (H-2k) mice remained susceptible. The resistance to reinfections was characterized by reduction of worm burdens between Days 6 and 14 postinfection. It was concluded that (1) resistance to N. dubius challenge infections is inherited in a dominant fashion and that multiple genes may influence such response, which in turn might be modulated by the Y chromosome; (2) both MHC and non-MHC genes may influence, in conjunction with the number of exposures to parasite antigens, the resistance to challenge infections.     

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite

Nippostrongylus brasiliensis: effects of immunity on the pre-intestinal and intestinal larval stages of the parasite. International journal for Parasitology4: 183–191. Migration of the pre-intestinal larval stages of N. brasiliensis was studied in rats undergoing either primary or challenge infections. In rats undergoing a primary infection, more than 67 percent of larvae successfully migrated from the skin to the oesophagus by 70 h after infection, and subsequently over 90 per cent of these larvae became established in the small intestine as sexually mature adults. In immune rats undergoing a second infection, 46 per cent of larvae completed migration to the oesophagus by 70 h and of these, only 1·6 per cent became established in the intestine to produce eggs. These inhibitory effects on the pre-intestinal and intestinal larval stages were even more pronounced in immune rats undergoing a third or fourth infection and in addition, there was a prolonged sojourn and substantial retention of larvae in their lungs. There was no evidence that the immune response had an adverse effect on oesophageal fourth stags larvae as these organisms (obtained from immune donors) were able to establish and develop to maturity when transferred per os to normal animals.Syngeneic transfer of immune mesenteric lymph node cells to normal recipients, caused expulsion of parasites from the intestine but failed to effect migration of pre-intestinal larval stages. The implications of these findings are discussed in the context of current knowledge of the mechanisms of immunity to helminths.     

Strongyloides ratti: Susceptibility to infection and resistance to reinfection in inbred strains of mice as assessed by excretion of larvae

Eleven inbred strains of mice, and one outbred strain, were infected with Strongyloides ratti and larvae in the faeces were quantitated. Three strains, C57B1/6, CBA and BALB/c mice were susceptible to infection while other strains demonstrated negligible infections as assessed by this method. Larvae were first seen in the faeces on day 5, peak levels were reached on days 6 and 7, and excretion ceased 10 days after infection. Factors influencing intensity of larval excretion were examined in C57B1/6 mice. Young mice (1 month of age) were found to be more susceptible to infection than 2 and 6 month old animals. Male mice were much more susceptible to infection than female animals. There was a direct relationship between the number of S. ratti injected and the number of larvae excreted over the range 200–1600 larvae; subsequent increments in dose of injected larvae failed to increase the larval output. Infection by the percutaneous route resulted in a heavier infection than did subcutaneous injection. Previous exposure to S. ratti induced a profound resistance to reinfection. It is suggested that S. ratti infections of C57B1/6 and CBA mice provide a useful model for the investigation of factors influencing the host-parasite relationship in strongyloidiasis.     

Taenia crassiceps: Immunity to metacestodes in BALB/c and BDF1 mice

The kinetics of primary and secondary infections with Taenia crassiceps larvae and the effects of immune serum on T. crassiceps larvae were studied in BALB/c and BDF1 mice. In both strains of mice a substantial degree of resistance to reinfection comparable to that previously reported in C3H mice can be induced by subcutaneous injection of three larvae 3 weeks prior to intraperitoneal challenge infection. Both early immune damage in the absence of adherent host cells and encapsulation by host cells are involved in rejection of larvae by BALB/c and BDF1 mice, but in both of these strains early immune damage is less pronounced and the cellular encapsulation response considerably more prominent than in the C3H mice studied previously. This difference is also reflected in the effect of immune serum on T. crassiceps metacestodes in vitro: immune serum from BALB/c and BDF1 mice is less effective than immune serum taken from C3H mice at comparable times after challenge infection in mediating damage to T. crassiceps larvae in vitro in the absence of host cells. These results suggest that genetically determined differences in immune capability can alter the state of equilibrium existing among different immune effector mechanisms without producing measurable effects upon overall host resistance to reinfection.     

Kinetics of primary and secondary infections with Taenia crassiceps metacestodes (Zeder, 1800) rudolphi, 1810 (cestoda: cyclophyllidea)

Siebert A. E. Jr., Good A. H. & Simmons J. E. 1978. Kinetics of primary and secondary infections with Taenia crassiceps metacestodes (Zeder, 1800) Rudolphi, 1810 (Cestoda: Cyclophyllidea). International journal for Parasitology8: 39–43. When three T. crassiceps metacestodes were inoculated intraperitoneally in mice as a primary infection, approximately 50% of the larvae recovered during the first 4 weeks after inoculation were found to be dead, while in mice primed by previous subcutaneous inoculation, about 85% of the larvae died. Larvae which survived the first 4 weeks following primary intraperitoneal inoculation reproduced asexually by exogenous budding and produced viable infections within the host mice. But larvae in secondary infections were encapsulated by host granulomata, failed to reproduce asexually, and did not produce viable infections. In mice given intraperitoneal inoculations of seven, ten and twenty metacestodes, fewer larvae were killed and little encapsulation response was noted, though host cells were common at the budding region of the larvae. Such a biphasic host-response to the infection has not previously been reported for larval cestode infections, and the reduction in host response associated with increased worm burdens may indicate possible depression of the host immune system.     

Trypanosoma cruzi: Correlation of resistance and susceptibility in infected inbred mice with the in vivo primary antibody response to sheep red blood cells

Nonspecific immune responses during the course of murine Trypanosoma cruzi infection were examined in mouse strains genetically resistant or susceptible to the Brazil strain of T. cruzi. Spleen cells from infected susceptible (C3H) or resistant [C57 B1/10 and FI (C3H × C57)]mice at various points during the course of infection exhibited a reduced response to concanavalin A and lipopolysaccharide in vitro. Since this reduced response occurred in both susceptible and resistant mice, it was not predictive of resistance or susceptibility in vivo. We next examined the kinetics of in vivo primary antibody response to sheep red blood cells (SRBC) in infected C3H and C57 mice. C3H mice exhibited inhibition of the direct plaque-forming cell assay (d-PFC) which persisted until death. In contrast C57 mice exhibited no inhibition of the response at Day 5 and subsequently a markedly augmented response was observed. Other strains of mice were similarly investigated: all the susceptible mice examined (A/J, BALB/c) showed inhibition or depression of the primary antibody response and resistant mice [B10Br, C57B1/10, SJL, F1 (C3H × C57)]demonstrated either no inhibition or considerable augmentation of this response. CS7 mice resistant to the Brazil strain were susceptible to the Tulahuén strain. The mice in this latter group exhibited a markedly significant inhibition of the in vivo primary antibody response to SRBC. Culture forms of the Brazil strain protected C3H mice from a virulent challenge. This immunization resulted in a markedly augmented antibody response. The data reported herein are consistent with the notion that inhibition of the primary antibody response to SRBC correlates with susceptibility whereas no inhibition or, indeed, augmentation of the response correlates with natural as well as acquired resistance.     

Mouse strain variation and effects of oocyst dose in infection of mice with Eimeria falciformis, a coccidian parasite of the large intestine

Stockdale P. G. H., Stockdale M. J., Rickard M. D. and Mitchell G. F. 1985. Mouse strain variation and effects of oocyst dose in infection of mice with Eimeria falciformis, a coccidian parasite of the large intestine, International Journal for Parasitology15: 447–452. Five inbred strains of mice and three hypothymic (nude) strains were infected orally with different doses of E. falciförmis oocysts. After resolution of primary infection as determined by faecal oocyst output, mice were challenged orally with a second dose of E. falciformis. Amongst the intact mice, BALB/c proved the most resistant to primary infection, while C3H/He mice were most susceptible, in terms of faecal oocyst production. Resistance was far more dramatic in BALB/c mice given high numbers of challenge oocysts. In terms of mortality at high oocyst doses, CBA/H were the most susceptible. All of the strains of mice were highly resistant to reinfection. In the case of nude mice, BALB/c. nu/nu were more susceptible than CBA/H.nu/nu or C57BL/6.nu/nu both in terms of faecal oocyst production and mortality. Thus the most resistant inbred mouse strain (BALB/c) is the least resistant in the absence of T cells. Unlike intact mice, nude mice showed no resistance to reinfection, this result being in line with previous work on this and other Eimeria spp. in nude mice.     

Cellular immune competence of a Drosophila mutant with neoplastic hematopoietic organs

In the Tum^l mutant of Drosophila melanogaster, the larval hematopoietic organs undergo neoplastic changes and release into circulation large numbers of blood cells. The lamellocytes, and to a lesser extent the plasmatocytes from which they are derived, are the cells that encapsulate various endogenous tissues and form melanotic tumors. The mutation is temperature sensitive, with maximum gene expression manifested at 29°C. The ability of Tum^l larvae to encapsulate eggs of the wasp parasite Leptopilina heterotoma is dependent not only on temperature, with host larvae much more immune reactive at 29°C than at lower temperatures (15° or 21°C), but also on the interval of time following infection when temperature shift experiments are performed. When the shift of parasitized larvae from 21° to 29°C is delayed by 18 hr the hosts are not as immune reactive as those shifted immediately after infection. Since Tum^l larvae are potentially highly immune reactive at the time of infection (with sufficient numbers of lamellocytes in circulation to encapsulate parasites), the low degree of immune competence in hosts shifted to 29°C after 18 hr or maintained at lower temperatures suggests that the increased capacity of blood cells to react against foreign surfaces is dependent on the cells acquiring new or altered recognition and adherence properties at 29°C. The 18-hr delay may provide the parasite with an opportunity to interfere with the acquisition of these specific cellular alterations. Differential hemocyte counts from parasitized larvae show abnormally low lamellocyte counts in susceptible hosts, indicating that successfully developing parasites interfere with the differentiation of hemocytes.     

Infection with Haemonchus contortus in sheep and the role of adaptive immunity in selection of the parasite

1988. Infection with Haemonchus contortus in sheep and the role of adaptive immunity in selection of the parasite. International Journal for Parasitology 18: 1071–1075. A series of infections with Haemonchus contortus in immune and non-immune sheep gave no indication that successive generations of the parasite were selected for the enhanced ability to cope with host-protective immunity. Separate subpopulations of the parasite were passaged through individual immune sheep and were compared at each generation with infections by the pooled populations in an additional panel of immune sheep. The experiment ceased when infections became too low to allow the production of sufficient infective larvae for reinfection. Results showed that H. contortus is unable to make adjustments to the immune status of a given sheep. Attention is thus diverted from the process through which host identifies self and non-self and from the histocompatibility system as the targets for possible antigen-mimicry by H. contortus.     

Trypanosoma musculi with Trichinella spiralis or Heligmosomoides polygyrus: concomitant infections in the mouse

Inbred mice infected with Trypanosoma musculi displayed wide variations in peak blood parasitemia. The most susceptible mice were C3H and A strain, while Balb/c, C57B1/6, and the related congenic B10 strains were the most resistant. The effect of an intestinal infection with either Trichinella spiralis or Heligmosomoides polygyrus on proliferation of T. musculi was investigated. T. spiralis infections given at the same time or up to 45 days before a T. musculi infection always caused an increase in blood parasitemia in C3H mice. Maximum increases were observed when T. spiralis infections preceded T. musculi by 5-10 days. In all mouse strains examined, dual infections increased maximum parasitemia by two- to four-fold, regardless of the degree of resistance of that mouse strain to either T. musculi or T. spiralis. This suggested that the immunological "cost" of a T. spiralis infection was the same for strains that were strong or weak responders to a primary infection with T. spiralis. In contrast, infection with H. polygyrus did not promote T. musculi parasitemia over the level of a single infection. The increase in blood parasitemia in T. spiralis-infected mice was largely due to the intestinal adult worm, but migratory larvae and mature muscle larvae also stimulated increased parasitemias. The increase in parasitemia was proportionate to the dose of T. spiralis, and the sex of the host did not affect the blood trypanosome level.     

The refractory responses of the White Swiss strain of Mus musculus to infection with Taenia taeniaeformis

Penetration of intestinal mucosa by oncospheres of Taenia taeniaeformis occurred among three age groups of White Swiss Mus musculus. Highest frequency of penetration was demonstrated among the 10–30 day-old group with the other two older groups, 40–60 and 70–100 days, each having succeedingly less penetration. The invasion process was more cytolytic than ground substance lysis; no difference in this process, or the reaction of the villi to it, was detected among the various age groups. Liver reaction, displayed by the same three age groups against larvae of T. taeniaeformis, was age dependent. Disorganization, loss of larval tissue integrity, and formation of a non-cellular capsule were demonstrated within 48 h in the 10–30 day group, while a rapid cellular response of inflammation and walling-off of larvae was seen in the 40–60 day group. No larvae were observed in the 70–100 day group.     

Susceptibility of several strains of mice to Echinostoma hortense infection

Susceptibilities of 5 different mice strains, including C3H/HeN, BALB/c, C57BL6, FvB and ICR, to Echinostoma hortense infection, was evaluated. The worm expulsion rate, worm size and egg production were observed from 1 to 8 weeks after infection with 30 metacercariae. C3H/HeN and ICR mice showed the highest worm maturation rates. The worm recovery rate and the number of eggs per gram (EPG) of feces was also higher in C3H/HeN and ICR mice than in BALB/c, C57BL6, and FvB mice. It is suggested that E. hortense is highly infectious to ICR and C3H/HeN mice, but not to the other strains of mice. Based on the results obtained, we believe that the susceptibility of different mouse strains to E. hortense infection is dependent on the genetic and immunologic background of mice.     

The larval feeding inhibition assay for the diagnosis of nematode anthelmintic resistance

A larval feeding assay for detection of nematode anthelmintic resistance to macrocyclic lactones and imidazothiazoles is described. The estimated concentration of anthelmintic required to inhibit larval feeding in 50% of L1's (IC50) that were resistant to either macrocyclic lactones or imidazothiazoles were significantly higher (P < or = 0.05) than those of susceptible isolates. Some variations in IC50 values were observed during the patent period of infection in all strains, although the pattern of the IC50 followed the same course. IC50 values varied in larvae developing from eggs shed throughout the patent period, with low values in the earliest larvae followed by higher values as the infection progressed, before decreasing at 70-90 days post-infection, although the low values of the first part of the patent period were not reached. However, the IC50 differences between all resistant and susceptible strains were significant throughout the whole patent period for ivermectin and levamisole. These results suggest that this technique may provide an alternative in vitro to detect anthelmintic resistance.     

Schistosoma japonicum: Infection characteristics in mice of various strains and a difference in the response to eggs

Female mice of 12 inbred strains were exposed to 20–25 cercariae of Schistosoma japonicum and infection status determined at day 40 by counting numbers of adult worms, eggs in faeces and eggs in a segment of liver. Most mouse strains appeared to be ‘permissive’ hosts although at least one strain (129/J) was shown to be relatively resistant in terms of day 40 adult worm numbers. In a radioisotopic lung assay for sensitivity to eggs, and developed as a rapid means of assessing granuloma formation, CBA/H mice were shown to differ from C57BL/6 mice in being non-responders. Histological examination of lungs of sensitized CBA/H and C57BL/6 mice injected intravenously with eggs established that granuloma formation was much more intense in C57BL/6 than CBA/H mice. Preliminary indications are that infected CBA/H mice are also low anti egg circumoval precipitin (COP) responders. Analysis of immune responses to isolated egg antigens in these two strains, and identification of the antigens of eggs to which such responses are directed in C57BL/6 mice, should provide insights into immunological disease processes (such as granulomatous inflammation) in this model system of japonicum schistosomiasis.     

Studies on resistance in snails. 5. Tissue reactions to Echinostoma lincloense in naturally resistant Biomphalaria glabrata.

Laboratory-raised juvenile albino Biomphalaria glabrata snails show a wide range of natural resistance to a single infection with 50 or 100 miracidia of Echinostoma lindoense. In the most resistant snails all sporocysts are destroyed in peripheral tissues soon after miracidial penetration. In less resistant snails some sporocysts reach the heart where they are encapsulated. In fully susceptible snails, all sporocysts rapidly migrate to the heart, where they mature and continue to develop. The greater part of our B. glabrata colony consists of snails in which sporocysts reaching the heart will survive, but in which a varying number of sporocysts will be destroyed in the tissues. These snails are usually considered susceptible, as they do become infected. Tissue reactions induced by sporocysts following a single infection in naturally resistant snails are similar to reactions in snails with an acquired resistance. In fully susceptible snails, the amebocyte-producing organ remains small and inactive. It is slightly to moderately stimulated in partially resistant snails in which destruction of sporocysts occurs in the tissues and surviving larvae are found in the ventricle. In snails in which amebocyte aggregates or capsules develop in the ventricle, the organ becomes markedly enlarged. Migration of sporocysts in the snail appears not to be continuous, as periodic rests seem to occur. Migration follows intrusion of the sporocyst through the tissues, induced by bodily distension and contraction, and then proceeds within the arteries against the blood flow, passing from one endothelial attachment site to another, possibly aided by negative pressure during ventricular diastole.     

Immunization and immunosuppression in mice reared for high or low immune responsiveness against Nema tospiroides dubius

High (H) and low (L) immune responder mice (Sitepu & Dobson, 1982) were immunized with 5, 10, 20, 40 or 80 Nematospiroides dubius larvae, drenched 3 weeks later with anthelmintic then challenged with 100 larvae. Size of the inoculum of larvae correlated positively with the numbers of N. dubius eggs passed in the faeces of all these mice after the immunizing dose, and the size of the inoculum of immunizing larvae was negatively correlated with faecal epg, worm numbers and lengths of worms recovered from H but not L mice after challenge infection with 100 larvae. Increasing the number of N. dubius larvae in the immunizing inoculum enhanced the immunization of H mice, whereas the L mice were progressively immunosuppressed by increasing numbers of larvae.     

Insight for Immunotherapy of HCMV Infection

Human cytomegalovirus (HCMV), a ubiquitous in humans, has a high prevalence rate. Young people are susceptible to HCMV infection in developing countries, while older individuals are more susceptible in developed countries. Most patients have no obvious symptoms from the primary infection. Studies have indicated that the virus has gradually adapted to the host immune system. Therefore, the control of HCMV infection requires strong immune modulation. With the recent advances in immunotherapy, its application to HCMV infections is receiving increasing attention. Here, we discuss the immune response to HCMV infection, the immune escape mechanism, and the different roles that HCMV plays in various types of immunotherapy, including vaccines, adoptive cell therapy, checkpoint blockade therapy, and targeted antibodies.