Publisher Summary A number of studies have been made on the variation in morphology of fluke-host snails, apart from the problem of taxonomy. In order to clarify the taxonomy of these snails, a study was made of 61 populations from 42 localities in New South Wales, South Australia, Queensland, Victoria and Tasmania, and some specimens forwarded by several collaborators in New Zealand. Two extreme morphological types, “A” and “B,” were recognized, and both serve as intermediate hosts for F.hepatica. Snails collected in the field showed great variations in shell and body and there were many intermediates between the extreme variants. In the assessment of various factors influencing the epidemiology and control of fascioliasis because of F. hepatica or F. gigantica, it should be assumed that all lymnaeid snails may aestivate for a considerable time during dry periods at both low and high temperatures. Empirical screening for new and more efficient anthelmintics against F. hepatica has been fairly successful, but has still failed to produce the ideal drug for safe, economic, and preventive medication of fascioliasis. More knowledge on the intermediary metabolism of F. hepatica, particularly of enzyme activity in the pathways, may lead to a new revolutionary approach for selecting a substance for the elimination of the parasites.

Experimental fascioliasis in Australia.

Publisher Summary This chapter discusses the delayed-type hypersensitivity (DTH), the prototype model of cellular immune phenomena as it occurs in mice. Most of the recent explosive development in the field of cellular immunology has emphasized the in vitro demonstrations of cellular responses to immunologic challenge and the various products of such stimulated cells, which possibly have in vivo phlogogenic or cytotoxic potential. However, before the full significance of cellular immune responses in in vivo situations can be determined, it will be necessary to transfer the in vitro observations to in vivo delayed hypersensitivity reactions. For this purpose, the mouse appears to be the most likely subject. Footpad tests, flank skin tests, and epicutaneous tests all have become well established and routinely used indicators of DTH in mice. The excellence of mice for studying the pathogenetic roles of DTH in infectious disease is well illustrated by a series of recent experiments on the formation of infectious granulomas around schistosome eggs, deposited in the lungs of mice by intravenous injection.

Delayed hypersensitivity in the mouse.

Resistance to fascioliasis — A review

The immunological response of rats to the intestinal phase of Trichinella spiralis was assessed using criteria derived from pervious studies with the nematode Nippostrongylus brasiliensis in rats and mice. In adult rats, the duration of infection with either parasite is similar and both infections are prolonged in young and lactating rats. As previously shown with N. brasiliensis, immunity to T. spiralis was transferred to recipients with antiserum or mesenteric lymph node cells from immune donors and antisera and cells given in combination had an additive effect. Signs of damage similar to that caused by antibodies in N. brasiliensis appeared in T. spiralis adult worms as the infection progressed and this damage occurred earlier in animals given antiserum or cells. On the basis of these results, it is concluded that the immunological control of adult T. spiralis requires both antibodies and cells, but the relative importance of these components and the way in which they affect T. spiralis requires further analysis.

The immune mechanism which expels the intestinal stage of Trichinella spiralis from rats.

Allergic inflammation as a hypothesis for the expulsion of worms from tissues: a review.

Studies on delayed (cellular) hypersensitivity in mice infected with trichinella spiralis. ii. transfer of peritoneal exudate cells.

The present results confirm those of the previous paper in this series by showing that peritoneal exudate cells transferred from infected donors cause a significant loss of adult worms in recipients given a challenging infection. In addition, the mice of these various studies were shown to be an isologous strain, and peritoneal exudate cells from uninfected donors had no demonstrable effect on worm elimination. On the basis of serologic, and, especially, intestinal histopathologic findings, additional evidence is provided to support the hypothesis that worm elimination is associated with delayed hypersensitivity. In the previous paper of this series (Larsh et al., 1964), evidence was presented to support an hypothesis that delayed hypersensitivity is involved in the mechanism that brings about the expulsion of adult Trichinella spiralis from mice. The present study was designed in an attempt to reproduce these results, showing that recipients lost significantly more adult worms than controls after a challenging infection. In addition, it was decided to obtain other information needed to test this working hypothesis. In the first place, it was necessary to determine definitely whether the mice used in these various experiments are an isologous strain, since this is a prime requirement in such transfer studies. Second, it was desirable to determine whether peritoneal exudate cells from uninfected donors are incompetent in that they have had no contact with parasite antigens. Third, it seemed of value to test the serologic responses of various groups of mice at specified periods. While available evidence fails to support the view that humoral antibodies play an important role in adult worm elimination, it was felt that serologic findings might shed light on the possibility that transferred peritoneal exudate cells set up an adoptive immune response. Finally, and most important, it was necessary in testing the present hypothesis to determine whether or not intestinal inflammation precedes the loss of adult worms. A characteristic inflammation in the anterior small intestine of our mice has been shown in Received for publication 12 July 1965. 146 various experiments to be directly responsible for worm elimination (Larsh, 1963). MATERIALS AND METHODS

Studies on delayed (cellular) hypersensitivity in mice infected with Trichinella spiralis. 3. Serologic and histopathologic findings in recipients given peritoneal exudate cells.

Demonstration of immunity to Fasciola hepática in recipient mice given peritoneal exúdate cells.

In 3 experiments, it was demonstrated that 2 injections of supernatant material, collected after disruption and centrifugation of larvae, combined with Freund's complete adjuvant sensitized donor mice sufficiently so that after injection of their spleen cells recipients showed immunity as indicated by a significant reduction in adult worms compared with controls 12 days after infection. The adjuvant alone did not contribute to this effect, since recipients injected with cells collected from donors given 2 injections of adjuvant alone harbored about the same number of worms as the regular controls. The value of using spleen cells in such studies in mice, and of isolating a single provocative antigen for use in future studies, is discussed. In the last two papers of this series (Larsh et al., 1964, 1966), peritoneal exudate cells collected from infected donors conferred immunity upon recipients as proved by a significantly lower adult worm burden than in controls after a challenging infection. Although it has been shown in guinea pigs that a single small dose of a crude saline-extract antigen from T. spiralis larvae injected intradermally produced delayed hypersensitivity, as demonstrated by skin tests, that was transferred to recipients by spleen cells (Kim, 1966) or lymph node cells (Kim et al., 1967), this has not been reported from studies in mice. Therefore, the present study was designed to determine whether a crude extract antigen would sensitize our donors sufficiently to confer immunity upon recipients after the transfer of cells. In this case, the success of sensitization would be manifested by a significant reduction in adult worms after a challenging infection. In 10 unsuccessful experiments with peritoneal exudate cells, separate variables, such as methods of antigen preparation, size of sensitizing doses, and routes of injections and schedules for production of sensitivity, were manipulated in attempts to demonstrate immunity. At this point, it was decided to use spleen cells for transfer. In the report that follows, positive results were obtained in three experiments where spleen cells were taken from donors after two injections of an antigenadjuvant mixture. The antigen was the superReceived for publication 11 October 1968. natant extract obtained by disruption of T. spiralis larvae in a Ten Broeck Tissue Grinder followed by centrifugation at 1,000 g for 20

Studies on delayed (cellular) hypersensitivity in mice infected with Trichinella spiralis. IV. Artificial sensitization of donors.

Rats given one infection showed a pronounced elevation of phospholipase B in the proximal half of the small intestine by the end of the 1st week, with a gradual decline to values within the range for uninfected controls by the 4th week. The distal half showed a more prolonged elevation, with a decline to the control range by the 5th week. Eosinophils (carriers of the enzyme) in the bone marrow were increased at days 5–21. At termination of the experiment on day 35, the marrow and combined gut activities had declined to normal levels. In the second experiment, rats infected once showed similar B activity in the gut and eosinophil production in the bone marrow to those noted in rats of the first experiment. However, rats challenged 37 days after the first infection showed earlier but less sustained B and eosinophil responses. This anamnestic-like response was also noted in the lungs, where the B activity was more pronounced and sustained than was evident in the once-infected rats. This association between marrow eosinopoiesis and B elevations is similar to that reported from studies with other parasite models, suggesting a common host response to tissue helminths worthy of study to determine its relation to the welfare of the host and/or detriment to the parasites.

Hilton T. Goulson

Papers

Studies on delayed (cellular) hypersensitivity in mice infected with trichinella spiralis. ii. transfer of peritoneal exudate cells.

Studies on delayed (cellular) hypersensitivity in mice infected with Trichinella spiralis. 3. Serologic and histopathologic findings in recipients given peritoneal exudate cells.

Demonstration of immunity to Fasciola hepática in recipient mice given peritoneal exúdate cells.

Studies on delayed (cellular) hypersensitivity in mice infected with Trichinella spiralis. IV. Artificial sensitization of donors.

Phospholipase B in nonsensitized and sensitized rats after challenge with Strongyloides ratti.