Background:  Freshly recovered monocytes from patients chronically infected with HIV-1 (viremic) exhibit an apoptotic signature in which a variety of genes related to apoptosis, such as the metallothionein gene (MT1), are differentially expressed and have been demonstrated to be associated with resistance to apoptosis-induced cell death (AICD). It is unknown how closely the observed in vivo apoptosis gene signature relates to regulation of AICD during an acute viremic episode associated with monocyte count changes in vivo or its relation to in vitro gene regulation following infection of macrophages. 

Methods:  Using archived peripheral blood mononuclear cells (PBMC) derived from whole blood of patients within a cohort undergoing structured treatment interruption or from seronegative donors resistance to AICD (cadmium [CdCl₂]), as measured by caspase-3 activation in T-cells and monocytes, we obtained monocyte vs CD4 T-cell counts and gene expression at the initiation and during a 4-week therapy interruption interval. Total RNA was isolated and amplified from CD14 monocytes or CD4 T cells. Gene expression as determined by quantitative real-time polymerase chain reaction (RT-PCR) was also compared between acute viral rebound (therapy interruption) and chronic viremia. Additionally, in vitro R5 HIV-1 infection monocyte-derived macrophages (MDM) from seronegative donors was analyzed, assessed for in vitro gene modulation as compared to in vivo alteration, and directly tested role of genes in AICD by SiRNA. 

Results: Increased monocyte counts following therapy interruption (p <0.03; median at week 0 to 400 and at week 4 to 500; 25% difference) was associated with viral rebound, a significant drop in CD4 T-cell count (p <0.05; 15% difference), increased resistance to AICD in monocyte but not in CD4⁺ T cells, and increased MT1 expression.  MT1 expression remained high before and after viral rebound and during chronic viremia in contrast to other apoptosis related genes examined.  MT1 expression was elevated following HIV-1 infection of macrophages in vitro and its inhibition increased AICD following CdCl₂ induction.

Conclusions:  We identified that in vivo changes in monocyte count can be associated with regulation of apoptosis and expression of MT1. This study shows a direct role for MT1 expression in resistance to induced apoptosis during HIV-1 infection in vitro and suggests a role for this gene in maintenance of monocyte/macrophage cells in vivo during HIV-1 infection.