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Specific antiparasitic agglutinins were detected in the plasma of normal chickens which recovered from infection with P. lophurae. These agglutinins were not detected in the plasma of bursaless birds which had been infected and reinfected. The administration of hyperimmune plasma to bursaless and intact birds resulted in greatly depressed parasitemias. Infected bursaless birds which were given normal plasma from adult cockerels demonstrated parasitemias which were depressed to the level of parasitemias of intact infected birds. This suggests that bursaless birds lack a natural protective substance (antibody), which birds normally develop. Splenectomized-infected birds which received hyperimmune plasma eventually recovered from an infection. Splenectomized controls, however, succumbed. The surviving splenectomized birds subsequently demonstrated an ability to control the parasites, as attempts to reinfect these birds failed. It is postulated that in the absence of the spleen and during intense antigenic stimulation, other lymphoid centers develop which are able to participate in normal anamnestic reactions. The bursa of Fabricius is a blind, ovoid, saclike structure found only in the class Aves. It is a primary lymphoid organ which is important in the development of the birds' ability to produce antibody, yet the bursa itself is not an immunologically competent organ. A bird hatched from an egg, the embryo of which has been treated with appropriate amounts of androgen, hatches without a bursa. In its adult life such a bird is unable to produce detectable antibody to a variety of antigens (Mueller et al., 1960; 1962). Cooper et al. (1965; 1966) described lymphoid centers in the spleen, including germinal centers and plasma cells, which are dependent upon the bursa for normal development. Since adult birds have no lymph nodes the spleen is apparently the most important secondary lymphoid organ of the bird. It functions directly in antibody production and phagocytosis. Taliaferro and Taliaferro (1955) stressed the importance of the splenic lymphoid-macrophage system in acquired immunity to malaria. They described a vigorous heteroplastic development of lymphoid elements into macrophages in the spleen in response to malarial infections. We have also shown that the spleen is necessary for the birds' recovery from primary and superinfections with our strain of Plasmodium lophurae (Longenecker et al., 1966). Most recently we have found that 6-weekReceived for publication 28 June 1968. old intact birds respond to a P. lophurae infection with a rise in beta-2 and gamma-i globulin, while bursaless birds do not respond (Longenecker et al., 1967). Since 6-week-old bursaless birds are less resistant than controls to primary infections with P. lophurae, we hypothesized that the lack of response of the beta-2 and gamma-1 globulins in these birds represented a deficiency in their ability to produce antibody against the parasite. Yet, these birds often recover from the infection and show excellent immunologic memory (Longenecker et al., 1966). In view of the fact that hormonally bursectomized chickens apparently do not produce detectable antibody, we have attempted to re-examine the role of antibody in combating avian malarial infections. This paper describes initial passive immunity experiments and attempts to further define the role of natural and acquired antibodies to the malarial parasite, P. lophurae. A second paper in this series (Congdon et al., 1969) describes measurements of natural and acquired antibodies in intact and bursaless birds using the sensitive indirect fluorescent antibody technique. MATERIALS AND METHODS |
