Biology Reference
In-Depth Information
9
Natural Killer Cells in HIV Infection and
Role in the Pathogenesis of AIDS
Benjamin Bonavida
Department of Microbiology, Immunology, and Molecular Genetics,
UCLA School of Medicine, University of California, Los Angeles, CA
INTRODUCTION
Natural killer ( NK) cells were originally de®ned functionally as a lymphocyte
subpopulation that spontaneously lysed tumor cells, virally infected cells,
and, in some instances, normal cells ( Herberman et al., 1975; Trinchieri, 1989,
1995). It is generally thought that NK cells represent a ®rst line of defense
against infectious agents and tumor growth. NK cells di¨er from T or B cells as
they do not express known T-cell receptors ( TCRs) or immunoglobulin ( Ig)
receptors for antigen. Unlike T cells, NK cells kill target cells in a non-major
histocompatibility complex (MHC)-restricted fashion (see Table 9.1 for general
properties of NK cells).
NK maturation can occur in the absence of a functional thymus, but NK
cells share with T cells a number of properties including the expression of CD7
and CD2 antigens and e¨ector functions such as cytolytic activity and cytokine
production. These shared properties support the notion that T and NK cells
may belong to the same or related lineages. Indeed, evidence exists suggesting
that functional NK and/or T lymphocytes can be derived from immature cell
precursors present in embryonic liver or thymus of mice and are included in a
small fraction of cells expressing the CD45 antigen (Sanchez et al., 1993). Pre-
cursors that are capable of undergoing in vitro di¨erentiation toward mature
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