Growth of Babesia bovis in bovine erythrocyte cultures.

Babesia bovis was cultured in a suspension of bovine erythrocytes incubated at 37 degrees C in Medium 199 with 50% bovine serum. The cells in culture were kept in suspension by slow stirring in spinner flasks and the medium was replaced at 24-hour intervals. Persistent multiplication of the parasite in a short series of subcultures suggests the feasibility of this approach for continuous culture.

T and B cell population changes in young and in adult rats infected with Plasmodium berghei.

Malaria infection in young rats is characterized by high parasitemia, severe anemia, and death. Parasitemia is lower in older rats, and the rats usually survive. This study was designed to investigate the immunological basis of this difference. T cell numbers in the thymuses and spleens of young (4 weeks old) and in adult (18 weeks old) infected and control rats were determined by killing with anti-theta serum and complement. The number of complement receptor lymphocytes (B cells) in spleens was determined after these cells had formed rosettes with sensitized, complement-coated sheep erythrocytes. Infection in young rats was characterized by progressive and severe thymic involution and by decreasing numbers of T and B cells in the spleen. In 18-week-old rats, T cell numbers in the spleen were slightly below those of controls early in infection but exceeded normal values by day 15. Progressive thymic involution was not a feature of infection in adult rats. The number of complement receptor lymphocytes in the spleens of adult rats decreased dramatically early in infection but were nearly normal by day 15. Severity of malarial infection in young rats is related to the inability of their lymphocytes to respond to Plasmodium berghei antigens early in infection in a way that leads to immunity.

Adoptive transfer of immunity to Plasmodium berghei with immune T and B lymphocytes.

Immunity to malarial infection may be transferred with immune lymphocytes. This study was designed to determine which lymphocyte type is responsible for the adoptive transfer of immunity to malarial infection. In one set of experiments, the ability of immune T and B lymphocytes, separated by passage through nylon-wool columns, to transfer immunity to infection was determined. In another experiment, the effect of killing T lymphocytes with anti-theta serum on the transfer of immunity was determined. The effect on the ability of immune lymphocyte suspensions to transfer immunity after B lymphocytes were removed from such suspensions by centrifugation on Ficoll-Hypaque gradients, after they had formed rosettes with sensitized, complement-coated sheep erythrocytes, was also determined. The ability of lymphocyte suspensions to adoptively transfer resistance to malarial infection was greatly impaired by the removal from the suspensions of differentiated B-type lymphocytes. Our results indicate that it is the differentiated B cell, most probably an antibody-producing cell, which lacks both theta antigen and the complement receptor that is responsible for conferring immunity to malaria.

Babesia sp.: the relationship of stage of development to structure of intra- and extracellular parasites.

The relationship of stage of development to structure in Babesia rodhaini and B. microti was studied by freeze-etching, carbon replication, and thin sectioning. The trophozoites of these Babesia are surrounded by a single membrane over most of their surfaces, but in some regions of the cytoplasm, membranous structures may parallel the plasmalemma, providing a double membrane. Merozoites are produced from trophozoites by budding. An early external indication that a bud will form is the organization of a pellicle complex at the site of the bud. The trophozoite nucleus divides before bud formation starts. The pellicle forms by development of a thick subplasmalemmal layer just under the plasmalemma in a bulging area that contains one of the daughter nuclei. The subplasmalemma layer of the pellicle of babesial merozoites is similar to that of plasmodial merozoites as it is divided into a series of roughly hexagonal plates by a reticular network which resembles coarse chicken wire. Thus, not only are the merozoites of these two species of Babesia budded in a fashion similar to that by which plasmodial merozoites are budded, but they also have similar pellicles.