The HIV-1 envelope protein gp120 impairs B cell proliferation by inducing TGF-ß1 production and FcRL4 expression.

The humoral immune response after acute infection with HIV-1 is delayed and ineffective. The HIV-1 envelope protein gp120 binds to and signals through integrin α4ß7 on T cells. We found that gp120 also bound to and signaled through α4ß7 on naive B cells, which resulted in an abortive proliferative response. In primary B cells, signaling by gp120 through α4ß7 resulted in increased expression of the immunosuppressive cytokine TGF-ß1 and FcRL4, an inhibitory receptor expressed on B cells. Coculture of B cells with HIV-1-infected autologous CD4(+) T cells also increased the expression of FcRL4 by B cells. Our findings indicated that in addition to mediating chronic activation of the immune system, viral proteins contributed directly to HIV-1-associated B cell dysfunction. Our studies identify a mechanism whereby the virus may subvert the early HIV-1-specific humoral immune response.

HIV-1 envelope protein binds to and signals through integrin alpha4beta7, the gut mucosal homing receptor for peripheral T cells.

Infection with human immunodeficiency virus 1 (HIV-1) results in the dissemination of virus to gut-associated lymphoid tissue. Subsequently, HIV-1 mediates massive depletion of gut CD4+ T cells, which contributes to HIV-1-induced immune dysfunction. The migration of lymphocytes to gut-associated lymphoid tissue is mediated by integrin alpha4beta7. We demonstrate here that the HIV-1 envelope protein gp120 bound to an activated form of alpha4beta7. This interaction was mediated by a tripeptide in the V2 loop of gp120, a peptide motif that mimics structures presented by the natural ligands of alpha4beta7. On CD4+ T cells, engagement of alpha4beta7 by gp120 resulted in rapid activation of LFA-1, the central integrin involved in the establishment of virological synapses, which facilitate efficient cell-to-cell spreading of HIV-1.

The genotype of early-transmitting HIV gp120s promotes α (4) ß(7)-reactivity, revealing α (4) ß(7) +/CD4+ T cells as key targets in mucosal transmission.

Mucosal transmission of HIV is inefficient. The virus must breach physical barriers before it infects mucosal CD4+ T cells. Low-level viral replication occurs initially in mucosal CD4+ T cells, but within days high-level replication occurs in Peyer's patches, the gut lamina propria and mesenteric lymph nodes. Understanding the early events in HIV transmission may provide valuable information relevant to the development of an HIV vaccine. The viral quasispecies in a donor contracts through a genetic bottleneck in the recipient, such that, in low-risk settings, infection is frequently established by a single founder virus. Early-transmitting viruses in subtypes A and C mucosal transmission tend to encode gp120s with reduced numbers of N-linked glycosylation sites at specific positions throughout the V1-V4 domains, relative to typical chronically replicating isolates in the donor quasispecies. The transmission advantage gained by the absence of these N-linked glycosylation sites is unknown. Using primary α4ß7/CD4+ T cells and a flow-cytometry based steady-state binding assay we show that the removal of transmission-associated N-linked glycosylation sites results in large increases in the specific reactivity of gp120 for integrin-α4ß7. High-affinity for integrin α4ß7, although not found in many gp120s, was observed in early-transmitting gp120s that we analyzed. Increased α4ß7 affinity is mediated by sequences encoded in gp120 V1/V2. α4ß7-reactivity was also influenced by N-linked glycosylation sites located in C3/V4. These results suggest that the genetic bottleneck that occurs after transmission may frequently involve a relative requirement for the productive infection of α4ß7+/CD4+ T cells. Early-transmitting gp120s were further distinguished by their dependence on avidity-effects to interact with CD4, suggesting that these gp120s bear unusual structural features not present in many well-characterized gp120s derived from chronically replicating viruses. Understanding the structural features that characterize early-transmitting gp120s may aid in the design of an effective gp120-based subunit vaccine.

The integrin alpha4beta7 forms a complex with cell-surface CD4 and defines a T-cell subset that is highly susceptible to infection by HIV-1.

Both activated and resting CD4(+) T cells in mucosal tissues play important roles in the earliest phases of infection after sexual transmission of HIV-1, a process that is inefficient. HIV-1 gp120 binds to integrin alpha(4)beta(7) (alpha(4)beta(7)), the gut mucosal homing receptor. We find that alpha(4)beta(7)(high) CD4(+) T cells are more susceptible to productive infection than are alpha(4)beta(7)(low-neg) CD4(+) T cells in part because this cellular subset is enriched with metabolically active CD4(+) T cells. alpha(4)beta(7)(high) CD4(+) T cells are CCR5(high) and CXCR4(low); on these cells, alpha(4)beta(7) appears in a complex with CD4. The specific affinity of gp120 for alpha(4)beta(7) provides a mechanism for HIV-1 to target activated cells that are critical for efficient virus propagation and dissemination following sexual transmission.

Long-term platelet production assessed in NOD/SCID mice injected with cord blood CD34+ cells, thrombopoietin-amplified in clinical grade serum-free culture.

OBJECTIVE: Delayed platelet recovery post-cord blood (CB) transplantation might be due to CB characteristics: low maturity of stem cell compartment, poor production of CD34+/CD41+ cells when induced to differentiate along the megakaryocytic (MK) lineage, retention of a low ploidy in the expanded MKs. Ex vivo expansion of CB hematopoietic progenitor cells for reconstitution of different human hematopoietic lineages has already been developed in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. However, optimal conditions for MK-progenitor engraftment to reduce hemorrhaging risk still to be developed. This study assesses the hypothesis that CB-CD34+ amplification with thrombopoietin (TPO) can be applied to a portion of a CB transplant unit to stimulate recovery along MK differentiation program. MATERIALS AND METHODS: Human CB-CD34+ cells were amplified in a serum-free, clinical grade medium with 100 ng/mL TPO alone and in addition to other cytokines (Kit ligand, interleukin-6, and Flt-3 ligand). Seven-day cultured cells were transplanted into irradiated NOD/SCID mice and engraftment, megakaryocytopoiesis, and platelet production were assessed. RESULTS: Platelet release was successful and continuously present for at least 8 weeks in NOD/SCID mice transplanted with CB cells stimulated by TPO. Thrombocytopoiesis was more effective with transplanted TPO-amplified cells than with the cytokine cocktails. CONCLUSION: Platelet number obtained is within the minimum level considered sufficient for hemostasis. Furthermore, amplified cells maintain their self-renewal capacity and multilineage potential differentiation. Thus, transplantation of TPO-expanded CB cells has the potential favoring both platelet recovery and human engraftment.

HDAC inhibition is associated to valproic acid induction of early megakaryocytic markers.

Valproic acid (VPA), a histone deacetylase inhibitor, causes differentiation in different cell lines and in a cell-specific manner; yet, its effect on megakaryocytic (MK) differentiation has not been studied. We evaluated whether VPA induces MK differentiation in a UT-7 cell line through histone acetylation in the GpIIIa gene region and activation of the ERK pathway. UT-7 cells, derived from megakaryoblastic leukemia, were treated with VPA at various concentrations, and the expression of differentiation markers as well as the gene expression profile was assessed. Flow cytometry, immunoblot analysis, and RT-PCR demonstrated that VPA induced the expression of the early MK markers GpIIIa (CD61) and GpIIb/IIIa (CD41) in a dose-dependent manner. The VPA-treated cells showed hyperacetylation of the histones H3 and H4; in particular, histone acetylation was found to have been associated with CD61 expression, in that the GpIIIa promoter showed H4 hyperacetylation, as demonstrated by the chromatin immunoprecipitation assay. Furthermore, activation of the ERK pathway was involved in VPA-mediated CD61/CD41 expression and in cell adhesion, as demonstrated by using the MEK/ERK inhibitor U0126. In conclusion, the capacity of VPA to commit UT-7 cells to MK differentiation is mediated by its inhibitory action on HDAC and the long-lived activation of ERK1/2.