H. Vandevelde et al., CD45RO(-CELLS BUT NOT CD45RA(+) NAIVE T-CELLS CAN BE EFFICIENTLY ACTIVATED BY REMOTE CO-STIMULATION WITH B7() MEMORY T), International immunology, 5(11), 1993, pp. 1483-1487
Co-stimulatory signals are absolutely required for T cell activation a
fter TCR - MHC-peptide interaction. The most important co-stimulatory
signal known so far is mediated by the interaction of CD28 on T cells
with B7 on APC. Here we demonstrate that the co-stimulatory signal fro
m the B7 molecule does not necessarily have to come from the same cell
which presents antigen. Titration curves obtained by limiting the amo
unt of anti-CD3 mAb suggests that the same amount of TCR - CD3 cross-l
inking is required for full T cell activation whether B7 is present on
the same or on another cell, but that the kinetics of T cell activati
on is slower when B7 is present on a separate cell from the primary si
gnal. Finally and most importantly we also show that CD45RO+ memory T
cells, but not CD45RA+ naive T cells, can be efficiently activated whe
n B7 is expressed on bystander cells. These findings imply that co-sti
mulatory activation requirements of B7 are more stringent for naive th
an for memory T cells, which could be an important mechanism involved
in the maintenance of self-tolerance.