| Summary: | 碩士 === 台北醫學院 === 細胞及分子生物研究所 === 85 === Human natural killer cells (NK) play important roles in innate
immune system and have the potential to regulate the adapted
immune responses. During a immune response, most activated
lymphocytes eventually died. Especially, restimulating activated
T cells by triggering CD3/TCR complex would make them undergo
apoptosis, a process termed as activation-induced cell death:
AICD. Thus, we intend to determine the occurrence of AICD on NK
cells and mechanisms directing the AICD. First of all, we
stimulated cells by the treatment of PMA/Ionophore or
crosslinking CD16 or Kp43 molecules on the surface of NK cells
,and found that by the treatment of PMA /Ionophore or
crosslinking CD16 molecules for 12-15 hours, 60-70% of short-
term cultured NK cells died in the form of apoptosis but not for
the crosslinking of Kp43 molecules. We further determine the
roles of Fas and LTbR, two members of TNF receptor super-family
in the AICD of NK cells. Through analysis toward surface
molecules on NK cells by Flow Cytometer, we have found that
freshly isolated NK cells could express low level of Fas
molecules, pretty high amounts of LTb and LTbR molecules but no
Fas ligand. Two-week in-vitro culture later, the only difference
is the enrichment of Fas molecules. By the treatment of PMA
/Ionophore or crosslinking CD16 molecules, Fas ligand molecules
were induced, Fas molecules were with same expressive pattern
but the expressive amounts of LTb and LTbR molecules were
significantly reduced to 30-50% of the original ones.
Stimulation upon crosslinking Kp43 molecules have no significant
effects on the expressive patterns of the four molecules. Then
we took advantage of Baculovirus protein expression system to
synthesize soluble Fas-Fc and soluble LTbR-Fc proteins and found
that s-Fas-Fc could prevent cells from apoptosis which resulted
from stimulation of PMA/Ionophore or cross- linking CD16 ,but s-
LTbR-Fc could not. Finally, the usage of IL-4 has been shown to
block the AICD of NK cells in a dose-dependent manner. In
summary, we proved that NK cells could undergo " AICD" upon
crosslinking the activation-receptor, CD16 and Fas mediated
apoptosis played the major roles in regulating AICD, but not for
LTbR mediated apoptosis. In contrast, signals delivered from
LTbR would inhibit apoptosis and therefor the interactions
betweem LTb and LTbR were essential for survival of human NK
cells.
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