TLR2-Activated B Cells are Phenotypically Similar to the Abnormal Circulating B Cells Seen Preceding the Diagnosis of AIDS-Related NHL Diagnosis

Abstract

Background AIDS-related non-Hodgkin lymphoma (AIDS-NHL) is a common AIDS-defining cancer. Prior studies suggest that chronic B cell activation precedes AIDS-NHL diagnosis. Activation of B cells by multiple factors, including Toll-like receptor (TLR) signaling, leads to the expression of activation-induced cytidine deaminase (AID), a DNA mutating molecule that can contribute to oncogene translocations/mutations, leading to NHL. The goal of this study was to determine whether surface markers expressed on activated and/or germinal center (GC) B cells, and AID expression, were elevated on circulating B cells preceding AIDS-NHL, as well as to determine if TLR signaling contributes to this activated B cell phenotype. Methods Stored viable peripheral blood mononuclear cell (PBMC) specimens, obtained prior to AIDS-NHL diagnosis, were assessed by multi-color flow cytometry. Additionally, B cells isolated from PBMC were exposed to TLR ligands in vitro, after which B cell phenotype was assessed by flow cytometry. Results An elevated fraction of B cells expressing CD10, CD71, or CD86 was seen in those who went on to develop AIDS-NHL. AID expression was detected in some who developed AIDS-NHL, but not in HIV+ or HIV− controls. TLR2- stimulated purified B cells exhibited the activated B cell phenotype observed in HIV+ subjects prior to AIDS-NHL diagnosis. Conclusions These results indicate that an elevated fraction of B cells display an activated/GC phenotype in those HIV+ subjects who go on to develop AIDS-NHL, and suggest that TLR2-mediated activation may play a role in HIV infection-associated B cell activation, potentially contributing to the genesis of AIDS-NHL.

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

“…Further, prior to an AIDS-NHL diagnosis, B cells exhibited abnormally elevated expression of activated and germinal center (GC) markers, including CD10, CD71, CD86, and AID, similarly to malignant cells identified in other Bcell malignancies [6,19,20]. Interestingly, we also determined that TLR2-stimulated B cells from healthy controls adopted this activated/germinal center-like phenotype [21].…”

“…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].…”

“…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).…”

“…Our prior data indicate that TLR2-activated B cells from healthy subjects mimic a peripheral activated/germinal center (GC)-like phenotype (CD19 + CD10 + CD71 + CD86 + AID hi ) that was observed in the blood of men in the MACS cohort prior to AIDS-NHL diagnosis [21]. AIDS-NHL largely develops from the malignant transformation of GC or post-GB B cells [26], suggesting that these activated/GC-like B-cells observed pre-AIDS-NHL diagnosis are potentially precursors of a malignant population.…”

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

“…Further, prior to an AIDS-NHL diagnosis, B cells exhibited abnormally elevated expression of activated and germinal center (GC) markers, including CD10, CD71, CD86, and AID, similarly to malignant cells identified in other B-cell malignancies [6, 19, 20]. Interestingly, we also determined that TLR2-stimulated B cells from healthy controls adopted this activated/germinal center-like phenotype [21]. …”