Sm. Mariani et al., THE APO-1 FAS (CD95) RECEPTOR IS EXPRESSED IN HOMOZYGOUS MRL/LPR MICE/, European Journal of Immunology, 24(12), 1994, pp. 3119-3123
APO-1/Fas (CD95) is a transmembrane receptor that transduces apoptotic
signals within various cells including T and B cells. The APO-1 gene
was found to be defective in lpr mice. In these mice insertion of a re
trotransposon gives rise to transcription of an abnormal mRNA and only
a fraction of wild-type APO-1 mRNA. It is not clear if lpr mice still
express wild-type APO-1 protein. To address this question, we prepare
d rabbit anti-APO-1 antibodies (Ab) with a peptide representing the ex
tracellular sequence corresponding to residues 5-23 of APO-1. The rabb
it Ab reacted with thymocytes from different mouse strains and the ext
ent of binding was correlated with the two known APO-1 alleles. In add
ition, the Ab reacted with mouse cell Lines expressing mouse APO-1 mRN
A but not with human cell lines. Binding of the Ab to MRL and BALB/c t
hymocytes was completely blocked by the immunizing peptide. Immunofluo
rescence analysis of MRL/lpr thymocytes showed that they still express
APO-1 protein at approximately one tenth of the wild-type expression
level on their surface. In addition, in lpr as in wild-type mice we fo
und a decrease of APO-1 expression in the more mature thymic compartme
nt. Western blot analysis of whole cell lysates from lpr and wild-type
thymocytes showed that the Ab recognized APO-1 in both cell types. Ap
proximately 50 % of CD3(+) splenocytes and 80 % of irt vitro activated
CD3(+) cells from wild-type mice reacted with the Ab, but to a lower
extent than thymocytes. The same differential reactivity was found in
lpr CD3(+) splenocytes. lpr T cells, however, showed a substantially l
ower level of APO-1. Thus, the differential expression of APO-1 on thy
mic versus peripheral lpr T cells might influence their sensitivity to
wards APO-1-mediated apoptosis.