Biology Reference
In-Depth Information
6
Cytotoxic T-Cell (CTL) Function
in HIV Infection
M. L. Garba and J. A. Frelinger
University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
INTRODUCTION
Adaptive immune responses to infectious agents have traditionally been classi-
®ed into humoral and cellular immune responses. Humoral immunity, medi-
ated by B cells is directed at extracellular pathogens whereas cellular immunity,
mediated by T cells is largely directed at intracellular pathogens including most
viruses. There is considerable overlap as these two types of immune responses
are not independent of each other. T cells produce cytokines that activate B
cells playing a role in humoral immunity. B cells in turn in¯uence cellular immu-
nity through antibody dependent cytotoxicity (ADCC) and function as highly
e½cient antigen presenting cells, especially for proteins that bind to their sur-
face immunoglobulins (Abdullah and Greenman, 1999; Patil and Gupte, 1995).
Cellular immunity is largely a function of lymphocytes and involves multiple
mechanisms and cell types. The ultimate goal of this immune response is to
remove the invading pathogen. The most well-de®ned mechanisms involved
include secretion of cytokines such as interferons ( IFN ) and interleukins ( IL) as
well as killing via the granule-exocytosis and the Fas/Fas ligand (Fas/FasL)
pathways ( Berke, 1989; Ramsay and Ramshaw, 1997).
Cytotoxic T lymphocytes (CTL) and natural killer (NK) cells (and lympho-
kine-activated killer cells, LAK) are responsible for the granule-exocytosis
pathway killing. This response is perforin dependent and involves the release
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