Inhibition of HIV-1 infection by viral chemokine U83A via high-affinity CCR5 interactions that block human chemokine-induced leukocyte chemotaxis and receptor internalization.

HIV-1 strains use C-C-chemokine receptor 5, CCR5, as a coreceptor for host transmission. Human CCR5 chemokine ligands inhibit binding and infection, whereas CCR5 mutations also inhibit infection by preventing surface expression, resulting in delayed progression to AIDS. Here, we describe a human herpesvirus 6 (HHV-6A) chemokine, U83A, which binds CCR5 with higher affinity than human chemokines, displacing their binding and leading to inhibition of chemotaxis of human leukocytes. Similarly, U83A inhibits infection by HIV-1 strains which use CCR5, but not the CXCR4, coreceptor. Unlike human CCR5 chemokine ligands which induce rapid CCR5 internalization mediated via clathrin, treatment with U83A prevents internalization. A spliced truncated U83A isoform, U83A-N, also binds CCR5 albeit with lower affinity, and this correlates with lower HIV-1 infection inhibition, whereas further truncation abolishes binding and any inhibition. Confocal microscopy confirms CCR5 internalization inhibition by U83A treatment, whereas labeled transferrin uptake shows that endocytosis via clathrin is unaltered. Previous results show that, although U83A-N is an antagonist, U83A is an agonist for CCR1, CCR4, CCR6, and CCR8 present on immune effector and antigen-presenting cells and here also shown for CCR5. Thus, U83A could act as a novel inhibitor of HIV-1 infection while also stimulating local immunity to the virus.

Identification and characterization of U83A viral chemokine, a broad and potent beta-chemokine agonist for human CCRs with unique selectivity and inhibition by spliced isoform.

Leukotropic human herpesvirus 6 (HHV-6) establishes a persistent infection associated with inflammatory diseases and encodes chemokines that could chemoattract leukocytes for infection or inflammation. HHV-6 variant A encodes a distant chemokine homolog, U83A, and a polymorphism promoting a secreted form was identified. U83A and three N-terminal modifications were expressed and purified, and activities were compared with a spliced truncated isoform, U83A-Npep. U83A efficiently and potently induced calcium mobilization in cells expressing single human CCR1, CCR4, CCR6, or CCR8, with EC50 values <10 nM. U83A also induced chemotaxis of Th2-like leukemic cells expressing CCR4 and CCR8. High-affinity binding, 0.4 nM, was demonstrated to CCR1 and CCR5 on monocytic/macrophage cells, and pretreatment with U83A or modified forms could block responses for endogenous ligands. U83A-Npep acted only as antagonist, efficiently blocking binding of CCL3 to CCR1 or CCR5 on differentiated monocytic/macrophage leukemic cells. Furthermore, CCL3 induction of calcium signaling via CCR1 and CCL1 induced chemotaxis via CCR8 in primary human leukocytes was inhibited. Thus, this blocking by the early expressed U83A-Npep could mediate immune evasion before finishing the replicative cycle. However, late in infection, when full-length U83A is made, chemoattraction of CCR1-, CCR4-, CCR5-, CCR6-, and CCR8-bearing monocytic/macrophage, dendritic, and T lymphocyte cells can facilitate dissemination via lytic and latent infection of these cells. This has further implications for neuroinflammatory diseases such as multiple sclerosis, where both cells bearing CCR1/CCR5 plus their ligands, as well as HHV-6A, have been linked. Applications also discussed include novel vaccines/immunotherapeutics for cancer and HIV as well as anti-inflammatories.

Genetic diversity and antigenic polymorphism in Plasmodium falciparum: extensive serological cross-reactivity between allelic variants of merozoite surface protein 2.

Diversity in the surface antigens of malaria parasites is generally assumed to be a mechanism for immune evasion, but there is little direct evidence that this leads to evasion of protective immunity. Here we show that alleles of the highly polymorphic merozoite surface protein 2 (MSP-2) can be grouped (within the known dimorphic families) into distinct serogroups; variants within a serogroup show extensive serological cross-reactivity. Cross-reactive epitopes are immunodominant, and responses to them may be boosted at the expense of responses to novel epitopes (original antigenic sin). The data imply that immune selection explains only some of the diversity in the msp-2 gene and that MSP-2 vaccines may need to include only a subset of the known variants in order to induce pan-reactive antibodies.