The longevity and infectivity of isolated populations of Plasmodium falciparum gametocytes were studied. Following chloroquine treatment gametocyte numbers fell with a constant rate of loss over a period of 16–24days; the populations had a half-life of 2·4 days. The sex ratio stayed constant throughout at 4 female:1 male. The ability of the microgametocytes to exflagellate and the infectivity of the population to mosquitoes persisted for 3 weeks. Antibodies to the gametocytes were detected but not in every patient studied. It was concluded that the gametocytes of P. falciparum are both long-lived and show persistent infectivity to mosquitoes. They can stimulatae antibody production but the immune response appears to play no part in their elimination, which probably takes place in the spleen as a part of the normal process of removing old, damaged and malformed red cells.

Mice which had been pre-treated with killed Corynebacterium parvum given intravenously or intraperitoneally, but not subcutaneously, were completely resistant ot infection withBabesia microti or B. rodhaini, and protected from death caused by Plasmodium vinckeior P. chabaudiinfection. There is evidence that the parasites died within circulating erythrocytes. This occurred much too soon for a specific antibody response to be evoked, and no antibody could be detected by the indirect fluorescent-anitbody technique. Thus it is suggested that a non-secific soluble mediator may play an important role in the protection observed.

After infection with Eimeria necatrix, chick intestinal cells undergo a profound increase in size. Herien, we describe methods for isolating and purifying infected cells containing second-generation schizonts at Various times post-infection. Our purification procoedures depended upon three fundamental properties of infected cells: namely (1) large size, (2) resistance to shearing and (3) decreased susceptibility to osmotic shock in hypotonic solutions. The availability of simple techniques for isolating infected whole cells should prove valuable in elucidating various intracellular aspects of infection during schizogony.

A procedure is described for the preparation of purified nuclei of chick intestinal cells infected with Eimeria necatrix. During second-generation schizogony the host-cell membrane becomes resistant to homogenization, hypotonic shock and ultrasonication. However, brief treatment with a low concentration of trypsin (0·001 ) will disrupt the cell membrane. Thereafter, the nuclei can be selectively harvested from contaminating nuclear types and schizonts by a series of centrifugations. Electron microscopy and Feulgen—DNA microspectrophotometry showed that the nuclear preparations retained their integrity with little, if any, loss of DNA. Chemical determinations confirmed that host-cell nuclear DNA synthesis was stimulated by conccidial infection and further established that quantitatively there was a coincident increase in the amount of host nuclear RNA during schizogony. It is now feasible to examine directly the effects of coccidial infection upon the host's nuclear apparatus.

A new technique for determining the trypanocidal activity of body fluids has been devised, using very small quantities in the wells of plastic microtest plates.

The activities of blood and tissue fluid of rabbits have been measured after the injection of melarsoprol, suramin, diminazene aceturate and isometamidium chloride. Activity against Trypanosoma (Trypanozoon)brucei Persisted in body fluids for a shorter time in treated normal rabbits than in treated rabbits infected with the tryponosome. The difference was caused by the participation of the immune response of the infected animals.

The new technique was sensitive enough to detect these interactions of chemotherapy and immunology and should be of use in the study of new trypanocidal compounds.

A variant-specific surface antigen from a cloned population of Trypanosoma brucei S 42 has been isolated and partically characterized. [35S]L-methionine was found to be incorporated into this material by cells incubated in vitro in a chemically defined medium. Incorporation of [35S]L-methionine was inhibited by cycloheximide and puromycin at concentrations which are known to specifically inhibit protein synthesis in other systems. The rate of synthesis of the variant-specific antigen in vitro has been estimated to be about 8% of the rate in vivo. Newly synthesized [35S]L-methionine-labelled variant-specific antigen was incorporated into the surface coat.

The multilaminate vesicles present in the tegument cytoplasm appear to fuse with side channels projecting out into the cytoplasm from the base of the surface pits. Their lamellate contents then unroll and spread out to form a trilaminate membranocalyx lining the pits and covering the tegument surface. The plant lectin concanavalin A appears to stabilize the process of vesicle fusion leading to an aggregation of multilaminate vesicles trapped in the lumen of the surface pits. The membranocalyx can be labelled with cationized ferritin. Chase incubations in normal medium indicate that by 4 h most of the label and the membranocalyx to which it is bound have been lost to the medium. This suggests that under the conditions of these experiments the membranocalyx has a half-life of 2–3 h.

A comparison was made of the ultrastructure, development and antigenic nature of the surfaces and of the viability of three types of schistosomula of Schistosoma mansoni: schistosomula formed afrer cercariae had penetrated isolated skin (SS), schistosomula produced after mechanical separation of cercarial tails from bodies (MS), and schistosomula transformed from cercariae after incubation in fresh rat serum (RS).

Within 2 h of transformation, the surface membrane of all three types of schistosomula had changed from trilaminate to heptalaminate structures and SS and MS had lost their cercarial glycocalyx. Initially a dense amorphous material was demonstrated on the surfaces of RS, which was thought to be the result of an interaction between a factor in rat serum and the glycocalyx: this material was greatly reduced within 2 h of transformation. The pre-acetabular glands of SS were emptied while those of MS and RS retained their contents. Immunofluorescent studies showed that all schistosomula bound serum from mice immune to S. mansoni, but the binding was stronger with MS and RS. The mixed agglutination reaction demonstrated the presence of human A and B blood group-like antigenic determinants on approximately 30% of 3 h old SS; these determinants were not detected on MS or RS. In vitro, the development of MS and RS was similar to SS; the first schistosomula reached the ‘gut-closed’ stage by day 10; 50–70% of SS reached this stage by day 12, in contrast to only 25–50% of MS and RS. Between 28 and 45% of all schistosomula developed to maturity when injected intravenously into mice.

It was concluded that the two types of artificially prepared schistosomula fultil the main criteria of transformation from cercaria to schistosomulum. Further, it is suggested that MS are the most appropriate source of material for immunochemical and physiological studies.

On parasitization with larval Brugia pahangi the infected flight muscle fibres of ‘resistant’ Anopheles labranchiae atroparvus undergo the following ultrastructural changes. The fibres become almost totally devoid of glycogen, their sarcoplasmic reticulum becomes elongate and closely associated with muscle fibrils. These fibrils degenerate and vesicles appear both within the degenerate fibril and within elements of the sarcoplasmic reticulum. Vesicles accumulate around the worm and degenerate to a uniform mass which eventually becomes melanized from its inner edge (next to the parasite) outwards.

The infected flight muscle fibres of both ‘resistant’ Aedes aegypti and ‘susceptible’ Aedes togoi are almost totally devoid of glycogen granules, but show no other ultrastructural change from the uninfected state.

The humoral immune response of plaice to infestations of selected metacercariae was studied. Precipitating antibodies to both Cryptocotyle lingua and Rhipidocotyle johnstonei were demonstrated using agar geldiffusion techniques. Immunochemical investigations of these antibodies indicated they were macroglobulins, resembling immunaglobulin M(IgM) of mammals. The rate and magnitude of antibody production by the host was determined by the ambient temperature

Wistar-Furth strain male rats and CFW strain male mice were immunized against Trichinella spiralis using an antegenic fraction derived from a cell-free homogenate of mature muscle larvae.

In rats, animlas immunized with 250 μg of antigen harboured singnificantly fewer (135000) muscle larvae 30 days after oral challenge than controls (231000). Furhter 7-day-old adult worms derived from immunized rats shed 48% fewer (P < 0·001) newborn larvae over a 24 h period in vitro than adult worms from non-immunized animals.

Mice were injected with either 10 or 100 μg of antigen. In comparison with non-immunized controls, mice immunized with 100μg of antigen harboured significantly fewer adult worms at days 7 and 9 after oral challenge infection, while female worms recovered from immune mice on days 6–10 after challenge shed fewer newborn larvae in vitro. Finally, mice immunized with 100μg of antigen harboured significantly fewer (10391) muscle larvae at 30 days after challenge than did controls (47750).

Immunization of mice with 10μ of antigen did not induce a statistically significant reduction in adult worms at either days 7 or 9 after challenge (P < 0·5). However, adult female worms from mice receiving 10μg of antigen still shed fewer larvae than did adults from control mice (P < 0·05). Mice immunized with 10μg of antigen harboured significantly fewer (13700) recoverable muscle larvae than did controls at 30 days after challenge (39000).