Extent and Dynamics of Polymorphism in the Malaria Vaccine Candidate Plasmodium falciparum Reticulocyte-Binding Protein Homologue-5 in Kalifabougou, Mali.

Reticulocyte-binding homologues (RH) are a ligand family that mediates merozoite invasion of erythrocytes in Plasmodium falciparum. Among the five members of this family identified so far, only P. falciparum reticulocyte-binding homologue-5 (PfRH5) has been found to be essential for parasite survival across strains that differ in virulence and route of host-cell invasion. Based on its essential role in invasion and early evidence of sequence conservation, PfRH5 has been prioritized for development as a vaccine candidate. However, little is known about the extent of genetic variability of RH5 in the field and the potential impact of such diversity on clinical outcomes or on vaccine evasion. Samples collected during a prospective cohort study of malaria incidence conducted in Kalifabougou, in southwestern Mali, were used to estimate genetic diversity, measure haplotype prevalence, and assess the within-host dynamics of PfRH5 variants over time and in relation to clinical malaria. A total of 10 nonsynonymous polymorphic sites were identified in the Pfrh5 gene, resulting in 13 haplotypes encoding unique protein variants. Four of these variants have not been previously observed. Plasmodium falciparum reticulocyte-binding homologue-5 had low amino acid haplotype (h = 0.58) and nucleotide (π = 0.00061) diversity. By contrast to other leading blood-stage malaria vaccine candidate antigens, amino acid differences were not associated with changes in the risk of febrile malaria in consecutive infections. Conserved B- and T-cell epitopes were identified. These results support the prioritization of PfRH5 for possible inclusion in a broadly cross-protective vaccine.

Secretion of oncostatin M by infiltrating neutrophils: regulation of IL-6 and chemokine expression in human mesothelial cells.

Recently, we identified that regulation of leukocyte recruitment by IL-6 requires shedding of the IL-6R from infiltrating neutrophils. In this study, experiments have examined whether other IL-6-related cytokines possess similar properties. Levels of oncostatin M (OSM) and leukemia inhibitory factor were analyzed in patients with overt bacterial peritonitis during the first 5 days of infection. Although no change in leukemia inhibitory factor was observed throughout the duration of infection, OSM was significantly elevated on day 1 and rapidly returned to baseline by days 2-3. The source of OSM was identified as the infiltrating neutrophils, and OSM levels correlated both with leukocyte numbers and i.p. soluble IL-6R (sIL-6R) levels. FACS analysis revealed that OSM receptor beta expression was restricted to human peritoneal mesothelial cells. Stimulation of human peritoneal mesothelial cells with OSM induced phosphorylation of gp130 and OSM receptor beta, which was accompanied by activation of STAT3 and secretion of CC chemokine ligand 2/monocyte chemoattractant protein-1 and IL-6. Although OSM itself did not modulate CXC chemokine ligand 8/IL-8 release, it effectively suppressed IL-1beta-mediated expression of this neutrophil-activating CXC chemokine. Moreover, OSM synergistically blocked IL-1beta-induced CXC chemokine ligand 8 secretion in combination with the IL-6/sIL-6R complex. Thus suggesting that OSM and sIL-6R release from infiltrating neutrophils may contribute to the temporal switch between neutrophil influx and mononuclear cell recruitment seen during acute inflammation.