Role of T-cell trafficking in the pathogenesis of HIV disease

The V2 domain of HIV gp120 mimics an interaction between CD4 and integrin ⍺4β7

The CD4 receptor, by stabilizing TCR-MHC II interactions, plays a central role in adaptive immunity. It also serves as the HIV docking receptor. The HIV gp120 envelope protein binds directly to CD4. This interaction is a prerequisite for viral entry. gp120 also binds to ⍺4β7, an integrin that is expressed on a subset of memory CD4+ T cells. HIV tropisms for CD4+ T cells and gut tissues are central features of HIV pathogenesis. We report that CD4 binds directly to ⍺4β7 in a dynamic way, consistent with a cis regulatory interaction. The molecular details of this interaction are related to the way in which gp120 interacts with both receptors. Like MAdCAM-1 and VCAM-1, two recognized ligands of ⍺4β7, the binding interface on CD4 includes 2 sites (1° and accessory), distributed across its two N-terminal IgSF domains (D1 and D2). The 1° site includes a sequence in the G β-strand of CD4 D2, KIDIV, that binds directly to ⍺4β7. This pentapeptide sequence occurs infrequently in eukaryotic proteins. However, a closely related and conserved sequence, KLDIV, appears in the V2 domain of gp120. KLDIV mediates gp120-⍺4β7 binding. The accessory ⍺4β7 binding site on CD4 includes Phe43. The Phe43 aromatic ring protrudes outward from one edge of a loop connecting the C'C" strands of CD4 D1. Phe43 is a principal contact for HIV gp120. It interacts with conserved residues in the recessed CD4 binding pocket. Substitution of Phe43 abrogates CD4 binding to both gp120 and ⍺4β7. As such, the interactions of gp120 with both CD4 and ⍺4β7 reflect elements of their interactions with each other. These findings indicate that gp120 specificities for CD4 and ⍺4β7 are interrelated and suggest that selective pressures which produced a CD4 tropic virus that replicates in gut tissues are linked to a dynamic interaction between these two receptors.

Host Restriction Factors Modulating HIV Latency and Replication in Macrophages

In addition to CD4⁺ T lymphocytes, myeloid cells and, particularly, differentiated macrophages are targets of human immunodeficiency virus type-1 (HIV-1) infection via the interaction of gp120Env with CD4 and CCR5 or CXCR4. Both T cells and macrophages support virus replication, although with substantial differences. In contrast to activated CD4⁺ T lymphocytes, HIV-1 replication in macrophages occurs in nondividing cells and it is characterized by the virtual absence of cytopathicity both in vitro and in vivo. These general features should be considered in evaluating the role of cell-associated restriction factors aiming at preventing or curtailing virus replication in macrophages and T cells, particularly in the context of designing strategies to tackle the viral reservoir in infected individuals receiving combination antiretroviral therapy. In this regard, we will here also discuss a model of reversible HIV-1 latency in primary human macrophages and the role of host factors determining the restriction or reactivation of virus replication in these cells.

miR-125b-5p inhibits cell proliferation by targeting ASCT2 and regulating the PI3K/AKT/mTOR pathway in an LPS-induced intestinal mucosa cell injury model

Intestinal barrier injury is an important cause of death in patients with acquired immune deficiency syndrome (AIDS). Therefore, it is of great significance to identify a therapeutic target for intestinal barrier injury to delay the progression of AIDS. microRNA (miRNA/miR)-125b-5p has an extensive role in cancer and controlling intestinal epithelial barrier function, but its role in human immunodeficiency virus-related intestinal mucosal damage remains unknown. The present study was designed to explore the effects of miR-125b-5p on lipopolysaccharide (LPS)-induced intestinal mucosal injury and the underlying mechanism. The expression of miR-125b-5p and ASCT2 mRNA was detected in colon biopsy samples of 10 patients with AIDS and 10 control healthy subjects. Human intestinal embryonic mucosa cells (CCC-HIE-2) were used to establish an LPS-induced intestinal mucosa cell injury model in vitro. Cell proliferation and apoptosis were determined by MTT assays and flow cytometry, respectively. miR-125b-5p levels and ASCT2 mRNA and protein expression levels in the LPS-induced intestinal mucosa cell injury model were detected by reverse transcription-quantitative PCR (RT-qPCR) and western blotting. The interaction between miR-125b-5p and ASCT2 was analyzed using a dual luciferase reporter assay. The results demonstrated that miR-125b-5p levels were increased and ASCT2 mRNA expression levels were decreased in colon samples from patients with AIDS and in LPS-induced intestinal mucosa cells. In the LPS-induced intestinal mucosa cell injury model, transfection with miR-125b-5p mimic inhibited cell proliferation and promoted cell apoptosis, while transfection with a miR-125b-5p inhibitor increased cell proliferation and attenuated cell apoptosis. Furthermore, miR-125b-5p mimic transfection resulted in a decrease of ASCT2 mRNA and protein expression, whereas the inhibitor increased ASCT2 mRNA and protein expression. Dual luciferase reporter assays suggested that ASCT2 was a direct target of miR-125b-5p, and its restoration weakened the effect of miR-125b-5p on LPS-induced intestinal mucosa cell injury. Transfection with the miR-125b-5p mimic also exhibited a suppressive effect on the PI3K/AKT/mTOR pathway in the LPS-induced intestinal mucosal cell injury model. Overall, the present study indicated that miR-125b-5p accelerated LPS-induced intestinal mucosa cell injury by targeting ASCT2 and upregulating the PI3K/AKT/mTOR pathway. The current findings may provide novel targets for the treatment of intestinal barrier injury in patients with AIDS.

Reduced immune-regulatory molecule expression on human colonic memory CD4 T cells in older adults

BACKGROUND

The etiology of the low-level chronic inflammatory state associated with aging is likely multifactorial, but a number of animal and human studies have implicated a functional decline of the gastrointestinal immune system as a potential driver. Gut tissue-resident memory T cells play critical roles in mediating protective immunity and in maintaining gut homeostasis, yet few studies have investigated the effect of aging on human gut T cell immunity. To determine if aging impacted CD4 T cell immunity in the human large intestine, we utilized multi-color flow cytometry to measure colonic lamina propria (LP) CD4 T cell frequencies and immune-modulatory marker expression in younger (mean ± SEM: 38 ± 1.5 yrs) and older (77 ± 1.6 yrs) adults. To determine cellular specificity, we evaluated colon LP CD8 T cell frequency and phenotype in the same donors. To probe tissue specificity, we evaluated the same panel of markers in peripheral blood (PB) CD4 T cells in a separate cohort of similarly aged persons.

RESULTS

Frequencies of colonic CD4 T cells as a fraction of total LP mononuclear cells were higher in older persons whereas absolute numbers of colonic LP CD4 T cells per gram of tissue were similar in both age groups. LP CD4 T cells from older versus younger persons exhibited reduced CTLA-4, PD-1 and Ki67 expression. Levels of Bcl-2, CD57, CD25 and percentages of activated CD38+HLA-DR+ CD4 T cells were similar in both age groups. In memory PB CD4 T cells, older age was only associated with increased CD57 expression. Significant age effects for LP CD8 T cells were only observed for CTLA-4 expression, with lower levels of expression observed on cells from older adults.

CONCLUSIONS

Greater age was associated with reduced expression of the co-inhibitory receptors CTLA-4 and PD-1 on LP CD4 T cells. Colonic LP CD8 T cells from older persons also displayed reduced CTLA-4 expression. These age-associated profiles were not observed in older PB memory CD4 T cells. The decline in co-inhibitory receptor expression on colonic LP T cells may contribute to local and systemic inflammation via a reduced ability to limit ongoing T cell responses to enteric microbial challenge.