Appearance of immature/transitional B cells in HIV-infected individuals with advanced disease: correlation with increased IL-7

Abstract

Progression of HIV disease is associated with the appearance of numerous B cell defects. We describe herein a population of immature/transitional B cells that is overly represented in the peripheral blood of individuals with advancing HIV disease. These B cells, identified by the expression of CD10, were unresponsive by proliferation to B cell receptor triggering and possessed a phenotype and an Ig diversity profile that confirmed their immature/transitional stage of differentiation. Consistent with an immature status, their lack of proliferation to B cell receptor triggering was reversed with CD40 ligand, but not B cell activation factor. Finally, levels of CD10 expression on B cells were directly correlated with serum levels of IL-7, suggesting that increased levels of IL-7 modulate human B cell maturation either directly or indirectly by means of a homeostatic effect on lymphopenia. Taken together, these data offer insight into human B cell development as well as B cell dysfunction in advanced HIV disease that may be linked to IL-7-dependent homeostatic events.

Fig. 1.

Analysis of CD10 expression on B cells from HIV-infected and HIV-negative individuals. (A) Profiles of expression for CD21, CD27, and CD10 are shown for one representative of each group: HIV-infected individuals with active disease (HIV group 1; CD4⁺ T cell counts <350 cells per μl and plasma viremia >10,000 copies of HIV RNA per ml); HIV-infected individuals with controlled disease (HIV-group 2; CD4⁺ T cell counts >500 cells per μl and undetectable HIV plasma viremia); and HIV-negative individuals. (B) Comparative analysis of levels of CD10 expression on B cells for the three groups of individuals defined in A.

Fig. 2.

Patterns of expression of cell surface markers on B cells of HIV-infected individuals with active disease depicting their immature/translational phenotype. Profiles are shown for one representative individual in group 1 of Fig. 1. Histograms are color coded to reflect expression of each marker within the three gates shown in the Top Left plot: CD10^hi/CD21^lo least mature B cells (blue), CD10^int/CD21^hi intermediate B cells (green), and CD10⁻/CD21^hi mature B cells (red).

Fig. 3.

Ig diversity analysis confirms the immaturity of CD10⁺ B cells. Shown is AluI restriction analysis of RT-PCR products on unfractionated and sorted CD10⁻ and CD10⁺ B cell fractions isolated from a representative HIV-infected individual with active disease (A) and an HIV-negative individual (B). The Ig VH3 diversity index is defined as the ratio of intensities of uncut PCR product (331 bp) in the presence (+) to uncut PCR product in the absence (−) of AluI. Bands of 45 and 57 bp represent AluI sites in CDR1, and the band of 71 bp represents an AluI site present in the framework region of certain members of the VH3 family.

Fig. 4.

Proliferative responses of CD10⁺ B cells are consistent with an immature status. Unfractionated and CD10/CD21-fractionated B cells were incubated for 72 h at 37°C in the absence or presence of various stimuli followed by measurement of proliferation. (A) Proliferation of unfractionated and CD10/CD21-fractionated B cells for one representative HIV-infected individual with active disease. (B) Combined analyses of proliferation for six HIV-infected individuals with active disease, depicted by fold enhancement of proliferation of the CD10⁻/CD21^hi over CD10⁺ B cell fractions.

Fig. 5.

Serum levels of IL-7 are inversely correlated with CD4⁺ T cell count (A), and directly correlated with both CD10 expression on B cells (B) and HIV RNA plasma levels (C).