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.     

Nematospiroides dubius: passive transfer of protective immunity to mice with monoclonal antibodies

Nine hybridoma cell lines secreting monoclonal antibodies specific for Nematospiroides dubius were produced by fusion of the mouse myeloma cell line NS-1 to either spleen cells or mesenteric lymph node cells from mice repeatedly infected with N. dubius. Seven of the antibodies were identified as IgM and two as IgG1. Each monoclonal antibody bound to polypeptide epitopes on both infective larvae (L3) and adult worms. However, five antibodies bound preferentially to L3 and three to adult worms. All nine antibodies reacted with high molecular weight protein antigens. Passive protective immunity in Balb/c mice was demonstrated with monoclonal antibodies Nd2 and Nd3 in ascites fluid which stunted both male and female worms and reduced parasite fecundity.     

Passive transfer of immunity to infection with Nematospiroides dubius from immunised mice to their offspring.

The results given below show that, whilst it is not possible to transfer immunity to infections with Nematospiroides dubius passively with serum from immune mice to normal adult mice, young born to immune females are resistant to this infection. The immunity is dependent on an intake of immunoglobulin via the milk for a period longer than 24 h. The passive transfer of immunity from immune mothers to neonatal mice does not appear to be dependent on a specific class of immunoglobulins.     

Suppression of heterologous immunity by Nematospiroides dubius antigens in vitro

The direct effect of the soluble antigens in the homogenate of adult Nematospiroides dubius (AH) on spleen cells from uninfected NIH mice was investigated using a Mishell-Dutton culture system. Parasite antigens were shown to reduce the plaque-forming cell (PFC) response to sheep red blood cells (SRBC) in a dose-dependent manner in vitro. A population of suppressor cells was demonstrated in the spleens of infected mice. Furthermore naive spleen cells cultured in the presence of AH gave rise to cells which depressed the PFC response of naive cells when subsequently cultured together in vitro. Treatment of these cell populations with anti-thy 1.2 plus complement did not impair suppressor activity, and it was concluded that cells expressing the T-cell phenotype were not involved.     

Nematospiroides dubius: factors affecting the primary response to SRBC in infected mice

Mice infected with Nematospiroides dubius were incapable of responding normally to i.p. or i.v. challenge with SRBC. The HA and PFC response to SRBC in infected animals was characterized by a severe depression of antibody to SRBC on day 4 and a reduced HA peak titre during the following week. The greatest depression of the response to SRBC was associated with an interval of 14 days between infection and the administration of antigen, suggesting that a particular stage of the parasite contributed significantly to immunodepression during this critical period. It was proposed that a combination of parasite induced damage to the intestine, release of parasite secretory/excretory products and loss of appetite by the host produced trauma during which the host was incapable of responding normally. However, mice given low-level and long-standing infections also showed reduced responses to SRBC, although these animals were not severely depressed. It is possible that this generalized weakening of host immunocompetence is the inevitable consequence of a parasite mechanism which operates more specifically to suppress the expression of homologous immunity at the intestinal level.     

Nematospiroides dubius: arrested development of larvae in immune mice.

When immune NIH mice were killed 10 days after a challenge infection with Nematospiroides dubius, approximately 10% of the inoculated larvae were recovered from the intestinal lumen, irrespective of the dose administered. When such mice were treated with cortisone from Day 10 for a period of 8 to 14 days and were subsequently killed for worm counts, it was found that they had significantly more worms than the immune control mice killed on Day 10. During the week following the beginning of treatment with cortisone there was little change in the low worm burdens in immune mice. However, 9 to 11 days after this treatment worm counts indicated that worms were accumulating in the intestinal lumen, and concurrently eggs were recorded in the feces of the mice. These observations indicated that a period of 9 to 11 days was required after the initiation of cortisone treatment on Day 10 for the worms in immune mice to complete their development to the adult lumen-dwelling stage. It is suggested that the larvae in the challenge infection became arrested early in their development in the intestinal wall and that growth resumed only after cortisone treatment. When treatment with cortisone was initiated later after challenge, it was still effective in reactivating arrested worms, but the lower worm recoveries in these mice indicated that the arrested larvae were being slowly rejected by the host. In subsequent experiments it was established that the arrested larvae of N. dubius were insusceptible to the activity of pyrantel embonate, an anthelmintic which is 99% effective against adult worms in the intestinal lumen. The mechanism whereby the larvae of N. dubius became arrested in immune mice and subsequently resumed their development after cortisone treatment is discussed.     

Genetic variation and host-parasite relations: Nematospiroides dubius in mice.

Our work deals with aspects of the genetics and immunology of host-parasite relationships as they influence the development of protective immunity and the phenomenon of coevolution. The aim is to understand parasitism through analyses of host specificity. In earlier studies we examined the inheritance of resistances in mice to infections with Nematospiroides dubius (=Heligmosomoides polygyrus) and established the predominant role played by antibodies in protective immunity. Here we report information concerning the selection of lines of N. dubius that differ in their ability to survive antagonistic immunological reactions from mice. Challenge infections with groups of these mice, immunized and protected by previous repeated infections, show that worms selected to survive the immunity that kills other worms do so by inhibiting the effectiveness of the cellular rather than humoral elements of protective immunity.     

Nematospiroides dubius: multiple infections in mice bred for immune responsiveness

Allogeneic mice were reared over 5 generations in a 2-way selection for high (H) and low (L) immune responsiveness to the intestinal trichostrongylid nematode Nematospiroides dubius. After 5 generations of selective breeding, the H mice passed fewer N. dubius eggs and harbored fewer, smaller and less fecund worms than did the L mice. These trends were observed after each of 4 consecutive infections, which were all treated with levamisole before reinfection. Further, more H than L mice were worm-free, and H mice were sensitized to sterile immunity by fewer infections than were needed by the L mice. These results encourage the view that the selective breeding of host species of agricultural importance is a valuable means of biologic control of nematodiasis.     

The suppression of homologous immunity by soluble adult antigens of Nematospiroides dubius

An established adult infection of Nematospiroides dubius was unaffected by the administration of immune lymphocytes and immune sera whereas an incoming larval infection was expelled. Past experiments have shown that the immune inoculum at least had the ability to recognize adult stages, leading to the hypothesis that adult stages secrete or excrete an immunomodulatory shield around themselves in the gastrointestinal tract. This hypothesis was given further credence by the demonstration that soluble antigens derived from adults abolished the generation of homologous immunity to this parasite. Modulation of immunity was reflected by increased fecundity, increased worm size, and increased survival time in the gut.