The large majority of the studies on B cells in HIV-1 infection have been performed in blood. Limited information is available on B cell populations from lymph nodes and on the association with the functional profile of T follicular helper (Tfh) cells.
We have investigated the distribution and frequencies of Env-specific B cells in lymph nodes and blood of 14 HIV-1 infected viremic individuals and 11 aviremic ART treated individuals using flow and mass cytometry. Lymph node mononuclear cells (LNMC) were stained with Env probes together with a B cell panel of 32 isotope-conjugated antibodies. LNMCs were stimulated with PMA/ionomycin for 6h and stained with a panel of 32 markers defining the phenotype and function of Tfh cells.
The frequency of Env-specific B cells was increased in LNs as compared to blood (1.5% vs 0.5%, p<0.0001) and in LNs of viremics as compared to treated (1.73 fold). In blood, Env-specific B cells were contained within the resting memory and activate memory phenotype while the majority of LN Env-specific B cells were contained within the Germinal Center (GC) (55% in viremics and 20% in treated) and switched memory (35% in viremics and 75% in treated) B cells. The percentage of Env-specific B cells within the GC directly correlated with viral load and with the number of total GC B cells. LN Env-specific B cells from viremics expressed decreased levels of BCL-2, CXCR4 and CXCR5 and increased levels of CD95, KI67, BCL6, FCRL4, CXCR3 and T-bet. In viremics, we found a significant increase (2-3 fold) in the Tfh cells defined by the CXCR3+T-bet+ phenotype and IFN-γ production along with a significant decrease (2-3 fold) in Tfh cells expressing CCR4, CCR6 and producing IL-4. The CXCR3/T-bet/ IFN-γ signature of Tfh cells was strongly associated with the appearance of Env-specific B cells expressing CXCR3 and T-bet. In vitro experiments demonstrated IFN-γ as the causative factor inducing the differentiation of the CXCR3+T-bet+ memory B cells and as a strong suppressive factor of antibody production.
The differences in composition of Env-specific B cells between blood and LN and the identification of Th1-like Tfh cells and IFN-γ as the main mechanisms affecting Env-specific B cell maturation will provide novel insights into strategies to develop optimal antibody responses in HIV infection and following vaccination.