CTLA-4, a cytotxic T lymphocyte associated antigen, was originally identified as a gene by a series of reverse genetic approaches. This molecule has been known to be homologous to CD28 , an accessory molecule providing costimulatory signal by
interacting with a B cell activation antigen B7/BB1. Itd has already been reported elsewhere that 34 KD CTLA-4 antigen is inducible in human peripheral blood lymphocyte(PBL) by various polyclonal mitogenic combinations including PHA, PMA+
ionomycin,
SEB, anti-CD2 antibodies. 9.1+9.6, and MLLR. This study was undertaken to determine which subset(s) of CE4+ and/or CD8+T cell in PBL expresses this molecule upon activatin. The expression ofd 34 KD CTLA-4 antigen in total PBL began at day 2,
peaked
at
day 3, continued upto day 5, and completely disappeared at day 7 of stimulation with irradiated murine OKT-3 only with the same stimulation used above. And the level of this expression was etectable at day 3 only with the same stimulation used
above.
And the level of tiis expression was 2-5% of that of total unpurified lymphocytes. Induction of this dmolecule in purified CD8+T lymphocyte followed similar time course of that in total in total lymphocytes though the level of expression was
15-20%
of
that of the total. And CD8+T lymphocyte was the only subset of PBL expressing the 34 KD CTLA-4 antigen upon stimulation either with anti-CD3 OKT3+ anti-CD28 9.3 monoclonal antibodies or Staphylococcal enterotoxin B + 9,3 monoclonal antibody. The
results
of this study suggest that a T cell activation antigen CTLA-4 is expressed both in CD4+ and CD8+ T subsets of PDL. But the major producer of this molecule is CD8+ T lymphocyte. And this subset can produce CTLA-4 by itself alone, but it seems that
helper
function of CD4+ T subset is required for the maximum expression of CTLA-4 by CD8+ T lymphocyte.
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