Antigenic variation in Babesia rodhaini demonstrated by immunization with irradiated parasites

1 Populations of Babesia rodhaini were isolated which were ‘putative’ variants of a reference population.

2. They were shown to have some antigenic dissimilarity to the reference population by comparing the response of rats immunized with irradiated parasites of the reference population, to challenge with either the reference population or with the variant populations. To the homologous challenge the immunized rats were strongly resistant. After a heterologous challenge, however, for the first 3 or 4 days the immunized rats showed no resistance but thereafter rapidly controlled the infection.

3. Five ‘variation’ populations were tested and all were shown to have some antigenic dissimilarity to the reference population. Two variant populations were compared and were not found to be identical with each other. There appeared, however, to be less dissimilarity between them and any one variant and the reference population.

Mrs J. Page and her successor Miss D. Leader, gave technical assistance. I thank my colleagues for helpful criticism of the manuscript.

Immunity of rats and mice following injection with 60Co irradiated Babesia rodhaini infected red cells

Babesia rodhaini infected mouse and rat red cells were non-infective after receiving 40 or 60 krad irradiation from a 60Co source.

Rats inoculated with irradiated infected red cells were subsequently found to show strong resistance to homologous challenge.

Mice, which are more susceptible to B. rodhaini, showed less resistance to challenge, following immunization with irradiated B. rodhaini infected red cells.

Splenectomized rats were immunized with irradiated infected blood. There was a delay compared with the controls in the onset of acute fatal parasitaemias in these rats. A population of parasites was isolated by taking and mixing blood from each of the splenectomized rats during the patent parasitaemia following challenge. This population appeared to be an antigenic variant of the original immunizing population.

I thank Mrs J. Page for excellent technical assistance and Dr K. N. Brown for criticizing the manuscript.

The role of the spleen in relation to natural and acquired immunity to infections of Babesia rodhaini in the rat

In the system investigated the spleen was essential in most rats for the acquisition of immunity and its maintenance in the presence of the piroplasm.

It is stressed that model immunological systems involving the role of the spleen do not simulate the complexity of a parasitic infection. The roles of the spleen as an antibody producer, and as a site of phagocytosis and haemopoiesis are discussed in relation to the control ofBabesia rodhainiby the rat. The possibility that the piroplasm may be able to undergo antigenic variation is considered.

The protective activity of serum from immune rats against Babesia rodhaini

Sera pooled from rats which were immune to Babesia rodhaini infection had demonstrable protective activity against the piroplasm in non-immune rats. When inoculated with parasites or close to the time of infection, antiserum caused a delay in the onset of patency but did not usually affect the course and severity of the patent parasitaemia in young rats. There were more survivors when antiserum was given in a series of small doses over a period rather than a single large inoculum at the time of infection. Serum from rats previously reinfected several times, when injected into infected rats during the early stages of patency, was followed by a rapid fall in parasite numbers. A severe secondary parasitaemia eventually ensued in these animals.

I would like to thank Dr S. F. Barnett for his advice during the work and Dr F. Hawking and my colleagues at Mill Hill for criticizing the manuscript. This work was carried out during the tenure of an Agricultural Research Council Studentship.

Babesia rodhaini infections in the rat after acute primary parasitaemia

Babesia rodhaini remains in the blood of most rats from 2 to 12 months after the acute primary parasitaemia has subsided. By analogy with some trypanosome and malaria infections it is suggested that piroplasms may have the capacity for antigenic variation, thus allowing the parasite to survive in the host for so long albeit as a chronic infection. A population of B. rodhaini was isolated which was considerably less sensitive in passive transfer experiments to two pools of serum from recovered rats than the normal passage population.

I thank Dr S. F. Barnett for his advice during the work and Dr F. Hawking and my colleagues at Mill Hill for criticizing the manuscript. This work was carried out during the tenure of an Agricultural Research Council Studentship.

A plea for simplicity in the classification of ankle fractures

1. Ashurst and Bromer's classification of ankle fractures is a useful one, but falls into the complexities of subdivision into sequential progression of severity, i.e. ‘degrees’ of fracture.

2. A similar criticism can be made of the Lauge-Hansen classification which has an added semantic disadvantage. Doubts are also cast upon the validity of the direct application of experimental results in cadaveric specimens to a clinical series.

3. A third classification, essentially a modified form of those preceding it but with both an anatomical and a functional basis is presented, in the belief that it can provide evidence of: (a) the mechanism of production and hence the achievement of reduction; and (b) the recognition of significant ligamentous damage, i.e. the recognition of major from minor, stable from unstable injuries—when used in association with radiographs taken while straining the ankle under anaesthesia.

4. An Appendix to the paper (pp. 210-211), giving a more detailed account of our revised classification, is included.