Tsugiye Shiroishi

The Duffy blood group determinants: their role in the susceptibility of human and animal erythrocytes to Plasmodium knowlesi malaria.

Duffy blood group negative erythrocytes from blacks are refractory to invasion by Plasmodium knowlesi merozoites in vitro, and blacks with this genotype are resistant to infection by P. vivax in vivo. In order to evaluate in a direct manner the role of Duffy blood group determinants in invasion by P. knowlesi merozoites, we studied erythrocytes from three rare non‐black Duffy negative individuals, Fy(a–b–), in whom the Duffy negative phenotype probably represents a mutation and not the introduction of the black Fy gene. These cells were resistant to invasion by P. knowlesi in vitro indicating that resistance to invasion is mediated by the FyFy genotype and not another closely linked factor. The erythrocyte receptors for invasion, however, may not be the Fya or Fyb Duffy antigens themselves, or at least not restricted to these determinants, since refractory Duffy negative human erythrocytes were invaded after treatment with trypsin or neuraminidase although these enzyme‐treated cells still lacked Fya and Fyb determinants. Furthermore, new world monkey erythrocytes and chymotrypsinized chimpanzee and kra monkey erythrocytes were invaded, although there was no serologic evidence of Fya or Fyb determinants on these cells.

Changes in Infectiousness of Malarial Gametocytes. II. Analysis of the possible Causative Factors.

The former paper (Huff and Marchbank, 1955) clearly indicated a general pattern among seven host-parasite combinations involving avian malarial parasites; this pattern being a rapid and continuing fall in the infectivity of gametocytes for mosquitoes during the course of infection in the bird. An analysis has been made in the present paper of the factors which might contribute to this change in infectivity of gametocytes. The aim has been the testing of two hypotheses to account for the decrease in this infectivity, namely (1) that it was due to a deficiency in the host which developed as the infection progressed, or (2) that an immune mechanism was responsible for the decrease. The following substances were administered to birds during the course of their infections: uninfected whole blood, coenzyme A, ferrous sulfate, sodium glutathione, calcium pantothenate, and sucrose. These substances did not enhance the infectivity of the gametocytes. In two experiments the hosts were bled daily during the course of their infections. No appreciable differences in oocysts numbers or infectivity values (oocyst-gametocyte ratios) were observed between the bled birds and the controls. Two experiments were performed testing whether mixed infections would yield evidence of a greater depleting effect. The results were not clearly conclusive but were suggestive that at least the principal cause of decrease in infectivity of the gametocytes was not a depleting effect. In one experiment in which blood infected with P. gallinaceum was transfused to a naturally immune host (duck) there was an appreciable increase in infectivity values of the mosquitoes. Two attempts to demonstrate effects on the gametocytes by the passive transfer of serum from hyperimmunized birds gave negative results. Two transfusion experiments were carried out in which infected blood was transmitted to birds with acquired immunity. No detectable change was observed in infectivity of gametocytes in one of these, while there were indications of a rapid fall in their infectivity in the second. Four experiments (three with P. gallinaceum in chickens and one with P. fallax in turkeys) testing the effect of immunization with killed parasites prior to the infecting inoculation uniformly indicated an early, more rapid fall in infectivity of gametocytes in the immunized than in the control animals. The results of all experiments can better be explained on the hypothesis that active immunity is the cause of decreasing infectivity of gametocytes than one in which this effect is assumed to result from a depletion effect of infection on the host. As in the former paper the lowering in mean numbers of merozoites produced by segmenters observed by other investigators during the crisis was not observed. However, significant differences were observed between the mean numbers of merozoites of infections in birds on adequate diets and those deficient in pantothenic acid.

Plasmodium knowlesi: Functional immunity and antimerozoite antibodies in rhesus monkeys after repeated infection

Abstract Three monkeys, after variable periods of infection with Plasmodium knowlesi , were cured and rechallenged with three strains of P. knowlesi . Functional immunity (a prolonged prepatent period and a modified course of parasitemia) was evident in only one of these monkeys. Sera obtained before each challenge were incubated with a mixture of normal and schizont-infected erythrocytes, and the inhibition of merozoite invasion of erythrocytes was evaluated in vitro . Some sera inhibited invasion. However, there was no correlation between functional immunity and this in vitro test. It appears from this study in monkeys and one in man that hosts with a high degree of functional immunity may not always have antibodies that inhibit merozoite invasion in vitro . Other methods for assessing functional immunity are needed.

Plasmodium cynomolgi: Influence of X-irradiation and sporozoite dilution on relapse patterns in infected rhesus monkeys

Abstract It has been possible to demonstrate a direct relationship between number of sporozoites in an inoculum and the number of subsequent relapses in experimental infections with Plasmodium cynomolgi. The reduction in Sporozoite numbers was accomplished through the use of two techniques; (1) X-irradiation and (2) volumetric dilution. The authors conclude that these observations tend to support a concept of latency as an explanation for relapse and delayed patency in malaria. It is difficult to reconcile these results with the generally accepted concept of a continuous cycle of liver schizogony in relapsing malarias.

Plasmodium gallinaceum: Selective immunosuppression by cyclophosphamide in preerythrocytic malaria

Abstract When chicks are injected with the immunosuppressant cyclophosphamide (Cy) on days 1 and 2 after hatching and then injected with sporozoites from infected mosquitoes on day 4, the normal susceptibility of only one host cell type to the sequential invasive stages of the preerythrocytic forms of avian malaria ( Plasmodium gallinaceum ) is increased. Thus, only endothelial cells lining capillaries showed an increased susceptibility to invasion or development of second generation preerythrocytic parasites. There is some indication that such an increased susceptibility also occurs after X-irradiation of chicks but not after treatment with endotoxin. Neither the infectivity or development of sporozoites within macrophages nor the invasion of erythrocytes by parasites released from the tissues was apparently affected by Cy-treatment of chicks. Neither suppression of natural anti-sporozoite humoral antibody nor the possibility of suppression of acquired immunity to preerythrocytic stages of the parasite was shown to be responsible for the observed increased parasitemia of Cy-treated chicks. The apparent specificity of the immunosuppression of a natural immunity was ascertained by inoculation of a selected preerythrocytic stage into Cy-treated and control birds, and, in addition, by observing the increased tissue parasite levels of spleens and brains of similarly treated birds after sporozoite inoculation when compared to controls.