Alanine mutagenesis of the primary antigenic escape residue cluster, c1, of apical membrane antigen 1.

Antibodies against apical membrane antigen 1 (AMA1) inhibit invasion of Plasmodium merozoites into red cells, and a large number of single nucleotide polymorphisms on AMA1 allow the parasite to escape inhibitory antibodies. The availability of a crystal structure makes it possible to test protein engineering strategies to develop a monovalent broadly reactive vaccine. Previously, we showed that a linear stretch of polymorphic residues (amino acids 187 to 207), localized within the C1 cluster on domain 1, conferred the highest level of escape from inhibitory antibodies, and these were termed antigenic escape residues (AER). Here we test the hypothesis that immunodampening the C1 AER will divert the immune system toward more conserved regions. We substituted seven C1 AER of the FVO strain Plasmodium falciparum AMA1 with alanine residues (ALA). The resulting ALA protein was less immunogenic than the native protein in rabbits. Anti-ALA antibodies contained a higher proportion of cross-reactive domain 2 and domain 3 antibodies and had higher avidity than anti-FVO. No overall enhancement of cross-reactive inhibitory activity was observed when anti-FVO and anti-ALA sera were compared for their ability to inhibit invasion. Alanine mutations at the C1 AER had shifted the immune response toward cross-strain-reactive epitopes that were noninhibitory, refuting the hypothesis but confirming the importance of the C1 cluster as an inhibitory epitope. We further demonstrate that naturally occurring polymorphisms that fall within the C1 cluster can predict escape from cross-strain invasion inhibition, reinforcing the importance of the C1 cluster genotype for antigenic categorization and allelic shift analyses in future phase 2b trials.

Recent long-distance dispersal overshadows ancient biogeographical patterns in a pantropical angiosperm family (Simaroubaceae, Sapindales).

Detailed biogeographic studies of pantropical clades are still relatively few, and those conducted to date typically use parsimony or event-based methods to reconstruct ancestral areas. In this study, a recently developed likelihood method for reconstructing ancestral areas (the dispersal-extinction cladogenesis [DEC] model) is applied to the angiosperm family Simaroubaceae, a geographically widespread and ecologically diverse clade of pantropical and temperate trees and shrubs. To estimate divergence dates in the family, Bayesian uncorrelated rates analyses and robust fossil calibrations are applied to the well-sampled and strongly supported phylogeny. For biogeographic analyses, the effects of parameter configurations in the DEC model are assessed for different possible ancestral ranges, and the likelihood method is compared with dispersal-vicariance analysis (DIVA). Regardless of the parameters used, likelihood analyses show a common pattern of multiple recent range shifts that overshadow reconstruction of events deeper in the family's history. DIVA produced results similar to the DEC model when ancestral ranges were restricted to two areas, but some improbable ancestral ranges were also observed. Simaroubaceae exhibit an early history of range expansion between major continental areas in the Northern Hemisphere, but reconstruction of ancestral areas for lineages diverging in the early Tertiary are sensitive to the parameters of the model used. A North American origin is suggested for the family, with migration via Beringia by ancestral taxa. In contrast to traditional views, long-distance dispersal events are common, particularly in the Late Oligocene and later. Notable dispersals are inferred to have occurred across the Atlantic Ocean in both directions, as well as between Africa and Asia, and around the Indian Ocean basin and Pacific islands.