Immunity to Babesia divergens in the Rat

Ben Musa, Najila (1988) Immunity to Babesia divergens in the Rat. PhD thesis, University of Glasgow.

Abstract

The rat adapted strain of B. divergens was used as a model to investigate the mechanisms of immunity to this parasite. The course of infection as well as the haematological changes that accompanied the infection were followed in splenectomised rats. The course of infection in splenectomised rats was short lasting (5-6 days) and no recrudescences were observed after the primary patent parasitaemia. The animals either died from the infection or recovered and were immune to challenge. The i. v. injection of 1.5 x 10e8 PRBC into splenectomised rats resulted in an infection from which most rats recover. The parasite, however, became more virulent with increasing passages and the injection of 1.5 x 10e8 PRBC resulted in a fatal disease. The drug diampron was used for treating infected rats. A single subcutaneous injection of diampron was enough to cure the animals. The acute parasitaemia was accompanied by severe anaemia evident as a drop in red blood cell counts. Red cell counts started returning to normal 8-10 days after recovery. Recovery from the infection was immediately followed by a pronounced blood leukocytosis which was predominately a lymphocytosis. The possibility that lymphocytes might be accumulating in the livers of immune rats was investigated. Histological studies showed the appearance of accumulation of cells around the central veins in the livers of immune splenectomised rats. These accumulations of cells have the appearance of "pseudofollicles" as described by Weiss (1985) in splenectomised gerbils infected with P. berghei. Preliminary histological studies have showed that some of these cells were B and T lymphocytes which might be important for the development and mediation of protective immunity in splenectomised rats. In splenectomised immune rats, the possible removal of B. divergens PRBC by the liver was investigated using Cr51 labelled PRBC. It is suggested that either the parasites within the red cells were opsonised and then removed by the liver where they were phagocytosed, or the merozoites may have been destroyed by antibody as they emerged from erythrocytes and the damaged red cells were removed by the liver. Irradiated parasites were injected into immune rats to determine whether it was intact PRBC or free merozoites which are cleared by the immune rats. It was concluded that immune splenectomised rats were able to clear PRBC from the blood stream and that immunity was not necessarily against merozoites. The effector mechanisms which were responsible for the destruction or removal of PRBC are unknown. The possible participation of humoral factors in acquired immunity to B. divergens was investigated. Antibodies to B. divergens were detected by the IFA test in sera collected during the infection and at different times after recovery. The antibody titre as measured by this test, rose from day 5 and reached a peak on day 19 at which level it remained for at least seven weeks. The possible role of antibody in protection was investigated in vivo by passive transfer with immune and hyperimmune serum. The levels of serum protection with immune sera rose rapidly from day 6 to reach a peak between day 7 and 13 and thereafter the levels declined rapidly. It was not possible to correlate protection with antibody levels measured by IFAT indicating that some antibodies to B. divergens were not protective. The role of antibody in protection was confirmed after fractionating immune and hyperimmune sera. The protective activity of sera collected immediately after recovery (day 7) was mainly due to IgM antibodies. The protective activity of sera collected 3-4 days after recovery (day 10) and of hyperimmune serum was mainly due to IgG antibodies. In hyperimmune sera, IgM antibodies were, however, partially protective. In order to compare the protective activity of immune sera in vivo with its effect on parasite growth in vitro, a method for cultivation of B. divergens was established. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Parasitology
• Date of Award: 1988
• Depositing User: Enlighten Team
• Unique ID: glathesis:1988-77820
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77820