Apoptotic death of infiltrating cells in human cardiac allografts is regulated by IL-2, FASL, and FLIP.
BACKGROUND
In vitro studies have shown that apoptotic cell death is triggered by a IL-2-dependent activation of the Fas-FasL pathway and that this pathway can be inhibited by FLIP.


METHODS
To define whether FLIP regulates apoptotic death of graft infiltrating T-cells during IL-2-mediated rejection, we analyzed endomyocardial biopsies (EMB) from cardiac allograft recipients for CD3, DNA strand breaks (TUNEL assay), FLIP (mRNA and protein), and FasL mRNA expression.


RESULTS
Apoptosis was present in CD3+ T-cell infiltrates. The number of TUNEL-stained mononuclear cells was inversely correlated with FLIP mRNA expression levels (P=.09). FLIP protein was present in 5% to 10% of the infiltrating cells and was constitutively produced by cardiomyocytes irrespective of the rejection grade. Rejection biopsies had elevated IL-2 and FasL mRNA expression levels compared to the expression levels before and after acute rejection (P=.03 and P=.11), while FLIP mRNA expression levels were significantly decreased during rejection (P=.05).


CONCLUSIONS
Our results indicate that during the IL-2-induced rejection process, infiltrated T cells become more sensitive to apoptosis.
de Groot-Kruseman
H A
HA
Department of Internal Medicine, University Medical Center Utrecht, The Netherlands.
Baan
C C
CC
Zondervan
P E
PE
de Weger
R A
RA
Niesters
H G M
HG
Balk
A H M M
AH
Weimar
W
W
D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD / Q000032:analysis; D017209:Apoptosis; D001483:Base Sequence; D017252:CD3 Complex / Q000032:analysis; D004249:DNA Damage; D017931:DNA Primers; D053222:Fas Ligand Protein; D005786:Gene Expression Regulation; D016027:Heart Transplantation / Q000473:pathology*; D006801:Humans; D020287:In Situ Nick-End Labeling; D007376:Interleukin-2 / Q000502:physiology*; D008562:Membrane Glycoproteins / Q000235:genetics*; D011506:Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013601:T-Lymphocytes / Q000276:immunology / Q000473:pathology; D014184:Transplantation, Homologous / Q000473:pathology
D048868:Adaptor Proteins, Signal Transducing; D015703:Antigens, CD; D017252:CD3 Complex; D017931:DNA Primers; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D007376:Interleukin-2; D008562:Membrane Glycoproteins; D011506:Proteins; D012333:RNA, Messenger; C434062:TNIP2 protein, human