Immunophenotypic Analysis of Peripheral Blood Mononuclear Cells Undergoing In Vitro Apoptosis After Isolation From Human Immunodeficiency Virus–Infected Children

Immunophenotypes, Apoptosis, and Expression of Fas and Bcl-2 From Peripheral Blood Lymphocytes in Patients With Secondary Early Syphilis

OBJECTIVES

Whether syphilis influences lymphocyte apoptosis has not been reported so far.

GOAL

The goals of this study were to determine whether syphilis influences lymphocyte apoptosis and to investigate the molecular mechanism of apoptosis.

STUDY DESIGN

Peripheral blood lymphocyte (PBL) immunophenotypes, apoptosis, and expression of Fas (CD95) and Bcl-2 were detected by flow cytometry in 33 patients with secondary early syphilis and 30 healthy subjects.

RESULTS

Compared with the control subjects, the percentage of CD4 T cells and the ratio of CD4:CD8 were significantly decreased, and that of CD8 T cells and the apoptotic rates of PBLs and CD4 T cells were obviously increased in syphilitic patients. Fas overexpression and Bcl-2 downexpression in the syphilitic group were observed in PBLs and CD4 cells but not in CD8 and CD19 cells.

CONCLUSIONS

The increased apoptosis of PBLs and CD4 T cells by Fas-mediated death pathway and downexpression of Bcl-2 protein could account for immune dysfunction in secondary early syphilis, which is responsible for the incomplete clearance of Treponema pallidum from the lesions and the chronic infection.

Partial activation and induction of apoptosis in CD4(+) and CD8(+) T lymphocytes by conformationally authentic noninfectious human immunodeficiency virus type 1

Increased levels of apoptosis are seen in human immunodeficiency virus (HIV) infection, and this has been proposed as an important mechanism contributing to HIV pathogenesis. However, interpretation of in vitro studies aimed at understanding HIV-related apoptosis has been complicated by the use of high concentrations of recombinant proteins or by direct cytopathic effects of replicating virus. We have developed an inactivation procedure that destroys retroviral infectivity while preserving the structural and functional integrity of the HIV surface proteins. These noninfectious virions interact authentically with target cells, providing a powerful tool to dissect mechanisms of HIV pathogenesis that do or do not require viral replication. Noninfectious CXCR4-tropic HIV-1 virions, but not microvesicles, partially activated freshly isolated CD4(+) and CD8(+) peripheral blood mononuclear cell T lymphocytes to express FasL and Fas, but not CD69 or CD25 (interleukin-2 receptor alpha) and eventually die via apoptosis starting 4 to 6 days postexposure. These effects required conformationally intact virions, as heat-denatured virions or equivalent amounts of recombinant gp120 did not induce apoptosis. The maximal apoptotic effect was dependent on major histocompatibility complex (MHC) class II proteins being present on the virion, but was not MHC restricted. The results suggest that the immunopathogenesis of HIV infection may not depend solely on direct cytopathic effects of HIV replication, but that effects due to noninfectious HIV-1 virions may also contribute importantly.

Mechanisms of HIV-associated lymphocyte apoptosis

Infection with the human immunodeficiency virus (HIV) is associated with a progressive decrease in CD4 T-cell number and a consequent impairment in host immune defenses. Analysis of T cells from patients infected with HIV, or of T cells infected in vitro with HIV, demonstrates a significant fraction of both infected and uninfected cells dying by apoptosis. The many mechanisms that contribute to HIV-associated lymphocyte apoptosis include chronic immunologic activation; gp120/160 ligation of the CD4 receptor; enhanced production of cytotoxic ligands or viral proteins by monocytes, macrophages, B cells, and CD8 T cells from HIV-infected patients that kill uninfected CD4 T cells; and direct infection of target cells by HIV, resulting in apoptosis. Although HIV infection results in T-cell apoptosis, under some circumstances HIV infection of resting T cells or macrophages does not result in apoptosis; this may be a critical step in the development of viral reservoirs. Recent therapies for HIV effectively reduce lymphoid and peripheral T-cell apoptosis, reduce viral replication, and enhance cellular immune competence; however, they do not alter viral reservoirs. Further understanding the regulation of apoptosis in HIV disease is required to develop novel immune-based therapies aimed at modifying HIV-induced apoptosis to the benefit of patients infected with HIV.