Vol. 25, No. 1
INFECTION AND IMMUNITY, July 1979, p. 249-254
0019-9567/79/07-0249/06$02.00/0
Immune Responses to Schistosoma mansoni in Rhesus Monkeys with Multiple Chronic and Early Primary Infections SHIRLEY E. MADDISON,1* SUSAN B. SLEMENDA,' GEORGE V. HILLYER,2 FRANCIS W. CHANDLER,3 AND IRVING G. KAGAN' Parasitology' and Pathology3 Divisions, Center for Disease Control, Atlanta, Georgia 30333, and Department of Biology, University of Puerto Rico, Rio Piedras, Puerto Rico 009312
Received for publication 13 March 1979
Immunological reactivity in 10 rhesus monkeys was monitored over a 22-week period. Cellular and humoral respones of three animals were studied after primary infection with Schistosoma mansoni. Two uninfected animals served as controls. Increased lymphocyte proliferative responsiveness to mitogens and adult worm antigen was evident during the prepatent period of the infection. Marked suppression of these responses occurred during the acute phase of the disease, but by weeks 9 and 11 the animals were again responsive to mitogens and antigen, respectively, and remained so throughout the remainder ofthe observation period. No antibody response to various cercarial, adult worm, and egg antigens could be detected until weeks 5 to 7, after which these responses also persisted. Comparison of the immunological reactivities of these animals with primary infection and those of five chronically infected immune animals indicated possible correlations between protective immunity and (i) strong Cercarienhiillenreaktion reactivity, and (ii) lymphocyte proliferative responsiveness to adult worm antigen. A number of reports (6, 9, 12) show that rhesus monkeys (Macaca mulatta) with primary infection with Schistosoma mansoni are protected against reinfection. They usually become immune 16 weeks after an initial infection with 100 cercariae (13), with protection being indicated by the absence of clinical signs of infection and absence of increased egg excretion after challenge exposure. The term "concomitant immunity" is used to describe this status of acquired immunity (14) in which a small number of egglaying adult worms from the primary infection persist and furnish a continuous immune stimulus both during and after the time that challenge schistosomes are destroyed. Schistosomes may persist in humans for as long as 20 years (15); but the more usual life span of the worms in a human host is probably 5 to 10 years (16). Experimental infection of mice with S. mansoni has an immunosuppressive effect on skin graft rejection (1), response to sheep erythrocytes (8), and lymphocyte proliferative response to nonspecific mitogens (10) and to S. mansoni antigen (4). In humans, suppression to specific adult worm and egg antigens and to concanavalin A (conA) has been observed during chronic schistosomiasis (2). In a group of Gambian boys heavily infected with S. haematobium, suppression of lymphocyte proliferation to the mitogen phytohemagglutinin (PHA) was observed (17). In the monkey, we have observed a depressed
lymphocyte proliferative response to both nonspecific mitogens and specific adult worm antigen during the acute phase of the disease (7). This suppression was, however, preceded by increased responsiveness to antigen during the prepatent period. In the same study, the experimental design entailed killing the animals 10 weeks after the primary exposure to cercariae to determine worm burdens (7). We now report on the immune responses of rhesus monkeys over a longer observation period (22 weeks) after primary infection. Once again, we observed the pattern of increased lymphocyte proliferative responsiveness to adult worm antigen during the prepatent period, subsequent suppression of responsiveness to T-cell mitogens and antigen during the acute phase of the infection, and later return of responsiveness to these specific and nonspecific stimulants. In addition, the immune responses of animals with chronic schistosome infections were studied after they were exposed to a challenge dose of cercariae of S. mansoni. MATERLkIS AND METHODS Monkeys. Male and female rhesus monkeys used
in this study were imported into the United States and conditioned by treatment with anthelminthics and antibiotics in the Animal Facility at the Center for Disease Control (CDC). Skin tests with old tuberculin were administered periodically throughout the experiment. 249
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(i) Chronically infected monkeys. The details of the duration of infections, numbers of exposures to 1,000 to 2,000 cercariae each, and the total numbers of cercariae used for the five chronically infected animals are listed in Table 1. The oldest animal in this study had been infected for 10 years. (ii) Animals with primary infection. Three monkeys imported into the United States the previous year at approximately 1.5 years of age were exposed to cercariae from the same batch and at the same time as were the chronically infected animals. (iii) Uninfected controls. Two monkeys imported into the United States the previous year and used as untreated, uninfected controls in the studies reported previously (7) were again used as untreated, uninfected controls in this study. Strain of S. mansoni and challenge exposure. The Puerto Rican strain of S. mansoni is routinely maintained in our laboratory in Biomphalaria glabrata and mice. In this study, monkeys in the chronic infection and primary infection groups were each exposed to 1,500 cercariae from the same pool by holding a shaved hand of each animal for 30 min in a beaker containing the cercarial suspension. Schistosoma egg counts. Egg output was quantitatively determined on 1-g portions of feces. The Formalin-ether concentration method (11) was used. Studies on peripheral blood. One week before challenge and at intervals after challenge, 9 ml of blood was drawn from the monkeys in groups i, ii, and iii. Total leukocyte and eosinophil (5) counts and lymphocyte proliferation assays were made. In addition, three portions of serum from each monkey were stored at
INFECTION AND IMMUNITY, July 1979, p. 249-254
0019-9567/79/07-0249/06$02.00/0
Immune Responses to Schistosoma mansoni in Rhesus Monkeys with Multiple Chronic and Early Primary Infections SHIRLEY E. MADDISON,1* SUSAN B. SLEMENDA,' GEORGE V. HILLYER,2 FRANCIS W. CHANDLER,3 AND IRVING G. KAGAN' Parasitology' and Pathology3 Divisions, Center for Disease Control, Atlanta, Georgia 30333, and Department of Biology, University of Puerto Rico, Rio Piedras, Puerto Rico 009312
Received for publication 13 March 1979
Immunological reactivity in 10 rhesus monkeys was monitored over a 22-week period. Cellular and humoral respones of three animals were studied after primary infection with Schistosoma mansoni. Two uninfected animals served as controls. Increased lymphocyte proliferative responsiveness to mitogens and adult worm antigen was evident during the prepatent period of the infection. Marked suppression of these responses occurred during the acute phase of the disease, but by weeks 9 and 11 the animals were again responsive to mitogens and antigen, respectively, and remained so throughout the remainder ofthe observation period. No antibody response to various cercarial, adult worm, and egg antigens could be detected until weeks 5 to 7, after which these responses also persisted. Comparison of the immunological reactivities of these animals with primary infection and those of five chronically infected immune animals indicated possible correlations between protective immunity and (i) strong Cercarienhiillenreaktion reactivity, and (ii) lymphocyte proliferative responsiveness to adult worm antigen. A number of reports (6, 9, 12) show that rhesus monkeys (Macaca mulatta) with primary infection with Schistosoma mansoni are protected against reinfection. They usually become immune 16 weeks after an initial infection with 100 cercariae (13), with protection being indicated by the absence of clinical signs of infection and absence of increased egg excretion after challenge exposure. The term "concomitant immunity" is used to describe this status of acquired immunity (14) in which a small number of egglaying adult worms from the primary infection persist and furnish a continuous immune stimulus both during and after the time that challenge schistosomes are destroyed. Schistosomes may persist in humans for as long as 20 years (15); but the more usual life span of the worms in a human host is probably 5 to 10 years (16). Experimental infection of mice with S. mansoni has an immunosuppressive effect on skin graft rejection (1), response to sheep erythrocytes (8), and lymphocyte proliferative response to nonspecific mitogens (10) and to S. mansoni antigen (4). In humans, suppression to specific adult worm and egg antigens and to concanavalin A (conA) has been observed during chronic schistosomiasis (2). In a group of Gambian boys heavily infected with S. haematobium, suppression of lymphocyte proliferation to the mitogen phytohemagglutinin (PHA) was observed (17). In the monkey, we have observed a depressed
lymphocyte proliferative response to both nonspecific mitogens and specific adult worm antigen during the acute phase of the disease (7). This suppression was, however, preceded by increased responsiveness to antigen during the prepatent period. In the same study, the experimental design entailed killing the animals 10 weeks after the primary exposure to cercariae to determine worm burdens (7). We now report on the immune responses of rhesus monkeys over a longer observation period (22 weeks) after primary infection. Once again, we observed the pattern of increased lymphocyte proliferative responsiveness to adult worm antigen during the prepatent period, subsequent suppression of responsiveness to T-cell mitogens and antigen during the acute phase of the infection, and later return of responsiveness to these specific and nonspecific stimulants. In addition, the immune responses of animals with chronic schistosome infections were studied after they were exposed to a challenge dose of cercariae of S. mansoni. MATERLkIS AND METHODS Monkeys. Male and female rhesus monkeys used
in this study were imported into the United States and conditioned by treatment with anthelminthics and antibiotics in the Animal Facility at the Center for Disease Control (CDC). Skin tests with old tuberculin were administered periodically throughout the experiment. 249
INFECT. IMMUN.
MADDISON ET AL.
250
(i) Chronically infected monkeys. The details of the duration of infections, numbers of exposures to 1,000 to 2,000 cercariae each, and the total numbers of cercariae used for the five chronically infected animals are listed in Table 1. The oldest animal in this study had been infected for 10 years. (ii) Animals with primary infection. Three monkeys imported into the United States the previous year at approximately 1.5 years of age were exposed to cercariae from the same batch and at the same time as were the chronically infected animals. (iii) Uninfected controls. Two monkeys imported into the United States the previous year and used as untreated, uninfected controls in the studies reported previously (7) were again used as untreated, uninfected controls in this study. Strain of S. mansoni and challenge exposure. The Puerto Rican strain of S. mansoni is routinely maintained in our laboratory in Biomphalaria glabrata and mice. In this study, monkeys in the chronic infection and primary infection groups were each exposed to 1,500 cercariae from the same pool by holding a shaved hand of each animal for 30 min in a beaker containing the cercarial suspension. Schistosoma egg counts. Egg output was quantitatively determined on 1-g portions of feces. The Formalin-ether concentration method (11) was used. Studies on peripheral blood. One week before challenge and at intervals after challenge, 9 ml of blood was drawn from the monkeys in groups i, ii, and iii. Total leukocyte and eosinophil (5) counts and lymphocyte proliferation assays were made. In addition, three portions of serum from each monkey were stored at
