A Role for TLR Signaling During B Cell Activation in Antiretroviral-Treated HIV Individuals

Abstract

The mechanisms underlying B cell activation that persists during antiretroviral therapy (ART) are unknown. Toll-like receptor (TLR) signaling is a critical mediator of innate cell activation and though B cells express TLRs, few studies have investigated a role for TLR signaling in B cell activation during HIV infection. We addressed this question by assessing the activated phenotype and TLR expression/responsiveness of B cells from ART-treated HIV-infected subjects (HIVART(+)). We evaluated activation markers implicated in B cell-mediated T cell trans infection during HIV pathogenesis. We found no significant difference in TLR expression between B cells of HIVART(+) and HIV(-) subjects. However, B cells of HIVART(+) subjects exhibited heightened endogenous expression levels of IL-6 (p=0.0051), T cell cognate ligands CD40 (p=0.0475), CD54 (p=0.0229), and phosphorylated p38 (p<0.0001), a marker of TLR signaling. In vitro, B cells of HIVART(+) individuals were less responsive to TLR stimulation compared to B cells of HIV(-) subjects. The activated phenotype of in vitro TLR-stimulated B cells of HIV(-) subjects was similar to ex vivo B cells from HIVART(+) individuals. TLR2 stimulation was a potent mediator of B cell activation, whereas B cells were least responsive to TLR4 stimulation. Compared to HIV(-) subjects, the serum level of lipoteichoic acid (TLR2 ligand) in HIVART(+) subjects was significantly higher (p=0.0207), correlating positively with viral load (p=0.0127, r=0.6453). Our data suggest that during HIV infection TLR-activated B cells may exert a pathogenic role and B cells from HIVART(+) subjects respond to in vitro TLR stimulation, yet exhibit a TLR tolerant phenotype suggesting prior in vivo TLR stimulation.

Immune Activation: Contribution to AIDS-Associated Non-Hodgkin Lymphoma

“…However, it is probable that microbial translocation contributes to this ongoing cytokine overproduction, as microbial molecules, including lipopolysaccharide and other toll-like receptor (TLR) ligands are known to potently stimulate cytokine production by macrophages and other immune system, and nonimmune system, cells. 51,112,113 Additionally, we have seen that exposure of human B cells to TLR ligands (TLR2 ligand) led to the development of a GC-like B cell phenotype, similar to that seen preceding the development of AIDS-NHL. 51,113 …”

Dysregulated B-cell TLR2 expression and elevated regulatory B-cell frequency precede the diagnosis of AIDS-related non-Hodgkin lymphoma

“…Further, we determined a significant positive correlation between B-cell TLR2 expression and the frequency of activated/GC-like B cells (Figure 1d, rho=0.7273, p=0.0379). Finally, we determined that compared to controls, cases exhibited higher, but not statistically significant (p=0.1), serum levels of the TLR2 ligand, lipoteichoic (LTA); LTA is a potent mediator of B-cell activation and elevated LTA serum levels in HIV-infected subjects is indicative of microbial translocation [10,21].…”

“…Though the mechanisms underlying HIV-associated B-cell activation are largely undefined, we demonstrated that Toll-like receptor ligands (TLR-L), resulting from HIV infection associated elevated microbial translocation [8,9], likely contributes to B-cell hyperactivation [10]. Additionally, prior work demonstrated that HIV infection is associated with elevated levels of several B cell stimulatory molecules, with increasingly heightened levels observed preceding AIDS-NHL diagnosis [6,7,11,12].…”

“…An association between the serum levels TLR4-ligand lipopolysaccharide (LPS) and the etiology of AIDS-NHL has been reported [25], suggesting that LPS stimulation contributes to B-cell hyperactivation, a critical driver of AIDS-NHL genesis. However, our previous data suggest TLR2 stimulation is a potent mediator of B-cell activation and HIV-infected subjects on ART exhibit higher serum levels of the TLR2-ligand lipoteichoic acid (LTA) [10] .…”

“…Prior to an AIDS-NHL diagnosis, there was a significant positive correlation between B-cell TLR2 expression and the frequency of activated/GC-like cells. Furthermore, the elevated serum levels of TLR2-ligand lipoteicoich acid (LTA), which is indicative of microbial translocation [10,21], suggest persistent TLR2 stimulation was associated with the development of AIDS-NHL. Interestingly, we did not find a difference in the serum levels of TLR9-ligand or bacterial DNA (not shown).…”