G.M. Urquhart

Immunological studies on Nippostrongylus brasiliensis infection in the rat: The role of local anaphylaxis

Abstract The role of local anaphylaxis in the immune expulsion of adult Nippostrongylus brasiliensis from the intestine of the rat has been investigated. The intravenous injection of the dye, Evans Blue, into rats harboring an infection of adult N. brasiliensis demonstrated areas of increased capillary permeability in the sites occupied by the worms. Anaphylactic reactions were produced when an extract of adult N. brasiliensis was injected into rats rendered immune either by previous infection or by serum transfer. The manifestations of this reaction in the gut were clearly seen when Evans Blue was injected intravenously along with the antigen. Neither the antihistamine substance, mepyramine maleate, nor the anti-5-hydroxy-tryptamine drug, lysergic acid, could abolish the anaphylactic reaction described above. Both compounds were also without effect on the self-cure reaction. The compound promethazine hydrochloride which has a more prolonged antihistaminic effect than mepyramine maleate did have some modifying influence on the self-cure reaction. A cortisone derivative, betamethasone, when administered from the 9th day of the infection was able to prevent the characteristic self-cure of an N. brasiliensis infection. This compound also prevented the anaphylactic reaction when adult antigen was injected into an immune rat. The results are discussed in relation to the mechanism of the self-cure reaction.

Immunological studies on Nippostrongylus brasiliensis infection in the rat: The “self-cure” phenomenon

Abstract Rats infected with 5000 Nippostrongylus brasiliensis larvae each, lose the infection almost completely in 20 days. This “self-cure” is due to an immune response on the part of the host. By transferring adult worms surgically to passively immunized and to normal rats, it has been shown that humoral antibody is important in interfering with the establishment of the parasites. Protective serum has no immediate lethal effect on N. brasiliensis in vitro nor does it immediately inhibit O2 uptake of the adult parasite when measured by Warburgs Direct Method. With the aid of Cr51 labeled erythrocytes, it has been shown that N. brasiliensis does not consume whole blood in any significant quantity. It is considered that antibody, against the parasite, may be protective because of its role in local anaphylaxis rather than direct actions on the worms.

Variables in X-Ray “inactivation” of Nippostrongylus brasiliensis larvae

Abstract Under the experimental conditions described it was concluded that (1) the inactivation of Nippostrongylus brasiliensis larvae by X-rays depends on the total dose of radiation administered and is independent of the rate of delivery within the range 235–735 r/minute; (2) in the X-ray inactivation of N. brasiliensis larvae the concentration of the larval suspension is unimportant within the range 50,000–9,000 larvae per milliliter. With larval suspensions as dilute as 1500 per milliliter, the inactivating effect of a standard dose of X-rays is enhanced; and (3) contamination of the larval suspension with fecal matter has no influence on the X-ray inactivation.

Self-cure of Haemonchus contortus infections under field conditions

The phenomenon of self-cure, as it occurred under field conditions in East Africa, was studied in Merino sheep infected with Haemonchus contortus . The onset of self-cure, as judged by a dramatic fall in faecal egg counts, was found to be simultaneous in sheep grazing on infected pasture and in sheep grazing on parasite-free pasture. Furthermore the results of autopsies carried out before and after self-cure showed that a marked and equal loss of adult worm burdens had also occurred. These results indicate that self-cure of H. contortus infections under natural conditions occurs in the absence of reinfection and is apparently non-immunological in origin. Since the phenomenon was always associated with a period of significant rainfall, it is suggested that new growth of pasture may be a significant aetiological factor.

Radioisotope studies on the anemia produced by infection with Fasciola hepatica.

Summary Red cells labelled with P32 and serum albumin labelled with I131 have been used to study the anemia associated with F. hepatica infections in rabbits and to make an estimate of the amount of the daily blood loss. The blood loss as calculated from P32 experiments is of sufficient magnitude to account for the anemia. When I131-labelled serum albumin and P32-labelled red cells were used simultaneously it was found that the P32/I131 ratio in the flukes was consistently higher than that in the blood. The use of radioisotope techniques in the study of this type of problem is discussed.

Immunological unresponsiveness to helminth parasites: I. The pattern of Nippostrongylus brasiliensis infection in young rats

Abstract The pattern of primary N. brasiliensis infections of different sizes is followed in young rats. When the number of worms that becomes established from the infecting dose is about 250 or less, worm expulsion as seen in adult rats does not occur. If considerably more than 250 worms are established, worm expulsion occurs, but is incomplete in comparison with that of adults in that it starts later, proceeds at a slower rate, and terminates when the worm population falls to a mean of approximately 200. These worm infections then persist until well into the adult life-of the rat. Attempts were made to interpret these facts in the light of published information on unresponsiveness and the self-cure reaction.

The rabbit as host in experimental fascioliasis

Abstract 1. 1. The possible factors which influence the number of adult flukes developing in a rabbit from a given number of cercariae are described. 2. 2. Experiments were carried out to determine the importance of some of these factors. 3. 3. It is concluded that two of the most important factors determining the number of flukes developing from a given number of 7-day old cercariae are the technique of infection and the natural resistance of the rabbit. 4. 4. Several methods of infecting rabbits with cercariae of F. hepatica are described and discussed, and details are given of a simple, rapid and efficient technique. 5. 5. The natural resistance of the sheep to infection with F. hepatica appears to be about the same level and within the same limits as that of the rabbit. 6. 6. When a technique of infection was used in which the cercariae were encysted on Cellophane and, when 7 days old, fed in cabbage in doses of 50 cercariae, the average number of flukes in 32 rabbits killed 63 days after infection was 18.6 ± 8.8. 7. 7. The breed and sex of the rabbits used or the use of cercariae from different snails played no significant part in determining the degree of infection.

Immunological unresponsiveness to helminth parasites. II. Antibody response and hypersensitivity reaction associated with Nippostrongylus brasiliensis infection in young rats.

Abstract We have previously shown that in rats infected when under 6 weeks of age with N. brasiliensis worm expulsion occurs only if more than 200 worms are established in the intestine. In such cases, worm expulsion starts later and proceeds at a slower rate than in comparatively infected adult rats stopping when a worm burden of 200 is reached. This relatively large residual infection persists into adult life. In the present paper the antibody status of rats infected when young was examined. Passive protection tests using the serum from such rats showed that protective antibody was produced by rats infected with more than 800 larvae, despite the fact that in these rats worm expulsion did not proceed to completion. It was also found that young rats produced reaginic antibody comparable in time of appearance and titer with similarly infected adults. Allergen production by the worms of the persistent infection was titrated and found to be produced in unreduced amount for at least 40 days after infection. Intestinal mast cell counts of the unresponsive rats were similar to those of infected adult rats. It was concluded that the incomplete expulsive reaction of rats infected when young cannot at present be explained by the absence of protective or reaginic antibodies or by a deficiency in the number of intestinal mast cells.

Immunological unresponsiveness to helminth parasites: III. Challenge of rats previously infected at an early age with Nippostrongylus brasiliensis

Abstract We have previously shown that when rats are infected when young with 500 N. brasiliensis larvae worm expulsion does not occur as in adult rats; instead rats so infected remain unresponsive to their intestinal worm burdens well into adult life. It was subsequently shown that this state is to a certain extent dose dependent in that infections of a greater size do result in a measure of worm expulsion but that this ceases when a burden of approximately 200 is reached; this also persists into the adult life of the rats. In this paper the response of rats infected when young to a subsequent challenge infection has been studied. Three factors have been found to be of importance in determining the type of response elicited: 1. (1) The size of the first infection given when young. Young rats initially infected with a small dose of larvae (500) respond to a challenge of 1000 larvae in adult life by a pattern of worm expulsion similar to rats experiencing a primary infection of N. brasiliensis , whereas rats initially infected with a large dose (3200) show a secondary type of response. 2. (2) The size of the challenge infection. Whereas removal of the original worm population by thiabendazole and its replacement with a similar small number of new worms (either by infection with larvae or by adult worm transplant) results in a primary type of worm expulsion, a large challenge infection (3000) larvae is capable of eliciting a secondary type of expulsion response despite an initial small infection. 3. (3) The age of the rats at the challenge infection. The superimposition of a challenge infection on a primary infection where both occur during the original unresponsive period (i.e. up to 7 weeks) results merely in a continuation of the unresponsive state into adult life although the worm burden is again adjusted to bring it down to a level of around 200 worms. It was concluded on several grounds that immune tolerance in the classical sense is not responsible for the persistence into adult life of the relatively large worm burdens acquired from infection during the immunologically unresponsive period. Alternative explanations and the significance of the phenomenon are discussed.