Microbiol. Rev., Dec 1996, 722-742, Vol 60, No. 4
KF Copeland and JL Heeney
T helper (Th) cells are of central importance in regulating many critical
immune effector mechanisms. The profile of cytokines produced by Th cells
correlates with the type of effector cells induced during the immune
response to foreign antigen. Th1 cells induce the cell- mediated immune
response, while Th2 cells drive antibody production. Th cells are the
preferential targets of human retroviruses. Infections with human T-cell
leukemia virus (HTLV) or human immunodeficiency virus (HIV) result in the
expansion of Th cells by the action of HTLV (adult T-cell leukemia) or the
progressive loss of T cells by the action of HIV (AIDS). Both retrovirus
infections impart a high-level activation state in the host immune cells as
well as systemically. However, diverging responses to this activation state
have contrasting effects on the Th-cell population. In HIV infection,
Th-cell loss has been attributed to several mechanisms, including a
selective elimination of cells by apoptosis. The induction of apoptosis in
HIV infection is complex, with many different pathways able to induce cell
death. In contrast, infection of Th cells with HTLV-1 affords the cell a
protective advantage against apoptosis. This advantage may allow the cell
to escape immune surveillance, providing the opportunity for the
development of Th-cell cancer. In this review, we will discuss the impact
of Th-cell activation and general immune activation on human retrovirus
expression with a focus upon Th-cell function and the progression to
disease.
Copyright © 1996, American Society for Microbiology
T helper cell activation and human retroviral pathogenesis
Department of Pathology, McMaster University, Hamilton, Ontario, Canada. copelndk@fhs.mcmaster.ca
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