HIV-1 induces phenotypic and functional perturbations of B cells in chronically infected individuals

A number of perturbations of B cells has been described in the setting of HIV infection; however, most remain poorly understood. To directly address the effect of HIV replication on B cell function, we investigated the capacity of B cells isolated from HIV-infected patients to respond to a variety of stimuli before and after reduction of viremia by effective antiretroviral therapy. B cells taken from patients with high levels of plasma viremia were defective in their proliferative responses to various stimuli. Viremia was also associated with the appearance of a subpopulation of B cells that expressed reduced levels of CD21. After fractionation into CD21(high)- and CD21(low)-expressing B cells, the CD21(low) fraction showed dramatically reduced proliferation in response to B cell stimuli and enhanced secretion of immunoglobulins when compared with the CD21(high) fraction. Electron microscopic analysis of each fraction revealed cells with plasmacytoid features in the CD21(low) B cell population but not in the CD21(high) fraction. These results indicate that HIV viremia induces the appearance of a subset of B cells whose function is impaired and which may be responsible for the hypergammaglobulinemia associated with HIV disease.

A unique syndrome of immunodeficiency and autoimmunity associated with absent T cell CD2 expression

CD2 is a glycoprotein expressed on the surface of human T cells that mediates adhesion between T cells and antigen presenting cells. CD2 also functions in concert with the T cell receptor to transduce signals that lead to T cell activation. The CD8 and CD4 molecules are transmembrane glycoproteins that are expressed on mutually exclusive populations of mature T cells and bind to determinants on major histocompatibility complex class I and class II molecules respectively. Like CD2, CD4 and CD8 function to promote adhesion between T cells and antigen presenting cells and potentiate signaling via the T cell receptor. We studied a patient with idiopathic lymphopenia and disseminated infection with Mycobacterium avium. The patient also suffered from recurrent deep venous thrombosis in association with anticardiolipin and anti-DNA antibodies. Peripheral blood T cells from this patient were polyclonal and expressed no detectable CD2 RNA or protein as determined by northern blotting, immunofluorescent staining with anti-CD2 antibodies, and failure to form rosettes with sheep red blood cells. In addition, the majority (85%) of this patient's T cells did not express either CD4 or CD8 but did express the alpha/beta T cell receptor. T cells from this patient failed to respond to stimulation with alloantigen or specific antigen. In contrast, there was a normal response to stimulation with immobilized anti-CD3 antibody. The clinical and immunologic findings in this patient provide in vivo evidence that the accessory molecules CD2, CD4, and CD8 play important roles in the regulation of normal human T cell activation.