Failure of Oriental Spargana to Immunize the Hypophysectomized Rat against the Sparganum Growth Factor of Spirometra mansonoides

Abstract

The rapid falling off of growth at 4 to 6 weeks that occurs in hypophysectomized rats implanted with spargana of Spirometra mansonoides, has been interpreted as an immune response. Asian spargana have no growth promoting effect on hypophysectomized rats, but will stimulate accelerated growth in normal mice. It was thus reasoned that if the plateau effect is an immune response, it should be possible to immunize hypophysectomized rats to the sparganum growth factor (SGF) of S. mansonoides by previous infection with Asian worms. After a 5 weeks "immunizing" infection with Asian worms, during which there was no appreciable change in the weight curve, the rats responded with sudden and rapid growth to a "challenge" injection of mansonoides scoleces. Apparently something other than immunity is involved in the typical reaction to SGF. The growth-promoting effect of Spirometra mansonoides infection in mice, hamsters, and hypophysectomized rats is well established (Mueller, 1963, 1965, 1968; Steelman et al., 1970, 1971; Garland and Daughaday, 1972). In mice and hamsters the effect is gradual and extends over the entire life span of the experimental animal (Mueller, 1965). In hypophysectomized rats the response differs in that there is a sudden dramatic spurt of growth, beginning within 24 to 48 hr of injecting the worms, and continuing for 4 to 6 weeks, when, in about three-fourths of the animals tested, the growth curve stabilizes (Mueller, 1972). It has been suggested (Mueller and Reed, 1968) that this plateau effect is due to an immune reaction on the part of the rat neutralizing the growth-promoting factor produced by the worm. Asian worms have approximately half as much growth-stimulating effect as S. mansonoides on normal intact mice, but little or no gross effect on hypophysectomized rats (Mueller, 1968, 1970b), although Glitzer and Steelman (1971) found subtle effects on individual organs. Bennett (1968), working with the Australian form, found that his experimental mice gained weight "at an abnormally high rate" as compared to the controls. His infected mice showed an advantage of approximately 12%. Received for publication 20 June 1972. * This investigation was aided by a USPHS, NIH, continuing grant, 2 R01 AI 01876-13, 14, 15. Since both S. mansonoides and Asian spirometrids have growth-promoting effects on mice, it would seem probable that their growth-promoting substances might have some structural similarity. If this is the case, prior infection with Asian worms should immunize against the sparganum growth factor (SGF) produced b S. mansonoides, and cancel out the weightgain response. This work was undertaken to test this hypothesis. MATERIALS AND METHODS The hypophysectomized rat is the preferred animal for assaying SGF (Mueller, 1968, 1972). Rats were purchased from Hormone Assay Laboratories, Inc., Chicago, Ill., as "90-gram, hypophysectomized males." Initial weights varied from 82 to 106 g. All rats were kept in large plastic cages and supplied with food and 10% sucrose solution ad lib., as described by Mueller (1972). The rats were weighed weekly and growth curves plotted for each rat. At 6 weeks the rats were sorted into 4 sets, and implanted with scoleces. Three rats received 5 Malay scoleces; three received 5 Australian, and three received 5 Taiwan. Three rats received 3 S. mansonoides scoleces each. The number was purposely reduced in this case since even a single scolex stimulates growth in the recipient animal (Mueller, 1970a). The rats were then maintained as before, and weights recorded weekly for a further 5 weeks. At that time all rats received a further injection of 5 S. mansonoides scoleces. Weights were again recorded weekly for each rat.