Ovalocytic erythrocytes from Melanesians in Papua New Guinea have been demonstrated to be resistant to infection by malaria parasites (Plamodium faldiparum) in culture by using a double-label fluorescence assay of merozoite invasion. That merozoites do not bind irreversibly to ovalocytes has been demonstrated by an-assay that measures competition between ovalocytes and normocytes. Analysis of behavior on thermal deformation has demonstrated that ovalocytes are more more thermostable than normocytes, suggesting that there is a major difference in cytoskeletal structure. These findings with P. faldparum and epidemiological data demonstrating clinical resistance to P. vivax and P. malariae suggest that the membrane alterations(s) in these ovalocytes affect(s) invasion step(s) common to all three species of malaria parasite.The relationship between human erythrocyte variants and susceptibility to malaria infection has been the subject ofintensive clinical and epidemiological study over several decades (1). The development of in vitro culture methods for Plasmodium falciparum (2) has recently permitted direct examination of the capacity of some of these variants to support parasite growth. Thus, under certain conditions, hemoglobin S (3), hemoglobin C (4), thalassemia, fetal hemoglobin, and glucose-6-phosphate dehydrogenase deficiency (5) limit the growth of the intraerythrocytic stages of P. falciparum.Invasion of erythrocytes by malaria parasites involves interaction with the host cell membrane (6, 7), and elucidation ofthe molecular events concerned is central to some approaches to development ofa malaria vaccine. In the case ofP. knowlesi and P. vivax, one component of erythrocyte specificity is represented by Duffy' blood group determinants (8) which are evidently involved in the formation oftightjunctions (9). However, the susceptibility ofOld World monkey erythrocytes, which are Duffy (fyb) positive (10), to P. knowlesi and their resistance to P. vivax implies that the binding requirements of the two species are not identical and that Duffy determinants alone do not fulfill these requirements. These determinants do not appear to be essential for recognition and penetration by other malaria species in man.The availability of human erythrocyte variants resistant to penetration by merozoites of several malaria species could be of help in identifying membrane components common to the process of erythrocyte recognition and entry by these species. In this context the observation, derived from population surveys among Melanesians in coastal Papua New Guinea hyperendemic. for malaria, that persons with ovalocytic erythrocytes have decreased rates of infection with P. vivax and P. malariae and apparently lower P. falciparum parasite densities (11) Erythrocytes. Ovalocytic individuals were identified by population screening using the erythrocyte morphological criteria of Amato and Booth (14). Blood samples from 10 unrelated ovalocytic individuals and 5 normocytic Melanesian controls in Papua New Guinea were co...
Aedes aegypti (L.) fed on rabbits immunized with mosquito antigens showed a reduction in fecundity in the first oviposition and decreased viability of the progeny. Feeding behaviour of mosquitoes was not affected and no significant mortality was observed due to the presence of anti-mosquito antibodies in the bloodmeal. Antibodies were detected in the oocytes of mosquitoes 48 h after the bloodmeal. The role of specific antibodies in influencing fecundity is discussed.
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