HOST-PARASITE RESISTANCE PATTERNS-SOME IMPLICATIONS FROM EXPERIMENTAL STUDIES WITH HELMINTHS*

Effect of mode of infection on the development and chemotherapeutic response of Hymenolepis nana in rats

The susceptibility of rats to Hymenolepis nana (Cestoda) and the chemotherapeutic response of anti-cestode drugs was studied during egg-induced and cysticercoid-induced infections. In cysticercoid-induced infection, the percentage of infected animals and the number of mature worms were significantly more than in egg-induced infection. The former mode of transmission required more drug to clear the parasites. These differences have been discussed on the basis of immunity engendered in the definitive host by the developing larvae.

Expulsion of Hymenolepis nana from mice with congenital deficiencies of IgE production or of mast cell development

The roles of IgE and mast cells on expulsion of adult Hymenolepis nana from the intestine were examined in mice. IgE-dependency was determined by comparing congenitally IgE-deficient SJA/9 and IgE-producing SJL/J mice infected with 50 H. nana eggs. Anti-H. nana IgE antibody was detected at three weeks post infection (p.i.) in SJL but not in SJA mice. The number of adult worms in the intestines of SJA and of SJL mice were similar at two weeks, but significantly more were found in SJA mice at three weeks p.i. Treatment of mice with anti-epsilon antibody also resulted in an increased worm burden at three weeks, suggesting participation of IgE in expulsion of H. nana. Intestinal mastocytosis was induced by infection regardless of the IgE status of the mice. Mast cell-dependency was tested in mast cell-deficient W/Wv and in normal littermate +/+ mice infected with 100 H. nana eggs. Anti-H. nana antibody was detected in both groups of mice at three weeks p.i. Worm expulsion seemed to be mast cell dependent because expulsion was less complete in W/Wv mice at three weeks p.i. Peripheral blood eosinophilia was comparable at three weeks p.i. in both IgE and mast cell sufficient and deficient mice. These results suggest that IgE and mast cells participate in the expulsion of H. nana adults from intestine in mice.

Hymenolepis nana: adoptive transfer of protective immunity and delayed type hypersensitivity response with mesenteric lymph node cells in mice

A marked degree of footpad swelling was observed in BALB/c mice infected with Hymenolepis nana eggs, when soluble egg antigen was injected into their footpads 4 to 21 days after the egg infection, indicating delayed type hypersensitivity responses in infected mice. Adoptive transfer with mesenteric lymph node cells from donor mice (BALB/c strain; +/+) infected with eggs 4 days before cell collection could confer this hypersensitivity to recipient nude mice (BALB/c strain; nu/nu). These mesenteric lymph node cells were then divided into two fractions, blast-enriched and blast-depleted cells, by density gradient centrifugation with Percoll. The recipients intravenously injected with the blast-depleted cell fraction showed a marked increase in footpad thickness, whereas the intravenous transfer of the blast-enriched cell fraction resulted in an insignificant increase in footpad thickness. The transfer of the blast-enriched cell fraction, but not of the blast-depleted cell fraction, conferred a strong adoptive immunity on syngeneic recipient nude mice, when the immunity transferred was assessed by examining cysticercoids developed in the intestinal villi on Day 4 of challenge infection. The lack of delayed type hypersensitivity response in mice that received the blast-enriched cell population was not due to a lack of the capacity of the cells to induce the response, because the cells were capable of inducing a significant increase in thickness of footpads of normal mice when these cells were locally injected into the footpad together with soluble egg antigen.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro oncospheral agglutination given by immune sera from mice infected, and rabbits injected, with eggs of Hymenolepis nana

Oncospheral agglutination given by sera immunized with Hymenolepis nana eggs is described as a new way of assessing H. nana infection. All sera of mice which possessed acquired protective immunity against reinfection by H. nana eggs had the potency to induce oncospheral agglutination in vitro. Only oncospheres, which had been hatched, agglutinated, no agglutination occurred in sera from uninfected mice. Oncospheral agglutination was carried out by mixing 0-1 ml of serial two-fold dilutions of serum and 0-1 ml of Hanks' balanced salt solution containing about 600 hatched oncospheres. Titre of agglutinins was indicated as a reciprocal of the final dilution capable of giving agglutination clusters made of three or more oncospheres. Agglutinins developed within 14 days after a primary infection with 500 shell-free eggs. There was no rapid increase of agglutinins within 4 days following a secondary infection. The titre increase coincided with the increase in dosages of eggs. Agglutinins were thought to be immunoglobulins, because the potency of the serum to agglutinate oncospheres was extinguished after absorption of globulins with rabbit anti-mouse globulin serum. Agglutinins were produced in rabbits by intravenous injections of shell-free eggs. The titres of the rabbit sera were much higher than those of mouse sera.

Population dynamics of Hymenolepis nana in mice: fecundity and the 'crowding effect'

Young white mice were infected with different doses of eggs or cysticercoids of Hymenolepis nana and the subsequent faecal egg output was measured over a 3-day period. This was then correlated with worm numbers, determined after killing the hosts. The longest worm in each infection was measured and it was shown that crowding decreased the linear dimensions, number of eggs per proglottis and rate of proglottis production of these worms, but that their shape was not affected.

The relation between total egg output and worm numbers was complex. In both egg-derived and cysticercoid-derived infections the egg production rose to a peak, fell and then levelled off to a constant rate with increasing worm numbers. Cysticercoid-derived worms were larger than egg-derived worms, but produced approximately the same number of eggs per unit of biomass. The differences in the egg output curves for the two types of infection were interpreted as being due to their size difference; this in turn may be a consequence of the host immunological response.

The effect of immunosuppressants on the development of Hymenolepis diminuta in mice

Cortisone, methotrexate and anti-lymphocyte serum were all found to suppress the rejection by SPF CFLP male mice of H. diminuta, which normally occurs between days 9 and 12. Worms continued to grow in mice given immunosuppressants and matured on days 16–18 as they would in a rat, by which time they stretched from the stomach to, and sometimes into, the caecum. Worms in mice given methotrexate ceased to grow after day 16, but this was believed to be due to the deterioration of the host's intestine wall; in mice receiving cortisone growth was faster than normal and worms continued to increase in size until the end of the experiments on days 20–24. The mouse/H. diminuta system is discussed, emphasizing that, as far as is known, H. diminuta (which has no hooks) has no close contact with the tissues and that this is a case of a mammal responding against an organism living freely in the lumen.