S. Lebelbinay et al., FURTHER CHARACTERIZATION OF CD82 IA4 ANTIGEN (TYPE-III SURFACE PROTEIN) - AN ACTIVATION/DIFFERENTIATION MARKER OF MONONUCLEAR-CELLS/, Cellular immunology, 154(2), 1994, pp. 468-483
The mononuclear cell surface protein IA4 was originally identified in
our lab using a mAb selected because of its strong reactivity with thr
ee lymphoblastoid variant cell lines which are HLA class I deficient,
are LAK susceptible, and form a high number of conjugates with LAK eff
ecters. We previously cloned the cDNA of the IA4 protein, coding for a
267-amino-acid type. III integral membrane protein, with four transme
mbrane domains and three possible N-glycosylation sites. The IA4 prote
in belongs to the tetra span transmembrane (TST) new family of surface
molecules, which also includes CD9, CD37, CD53, CD63, and TAPA-1. IA4
antigen was recently recognized as belonging to a new cluster of diff
erentiation CD82 (International CD Workshop, Boston 1993). The IA4 ant
igen expression pattern at the surface of immune cells from normal don
ors was studied. On T lymphocytes, IA4 was barely detectable on restin
g cells and increased 3.5- to 7-fold following PHA or PHA + PMA stimul
ation. This IA4 increased expression is correlated with the morphologi
c change in blast cells and with the expression of activation markers
such as CD2 and MHC class II antigens, therefore suggesting that IA4 i
s an activation marker on T lymphocytes. The expression of IA4 was low
on circulating resting monocytes collected by elutriation. However, t
hese monocytes, cultured in medium alone or with GM-CSF, acquired the
morphology of macrophage and simultaneously overexpressed MHC Class II
, CD14, and IA4 antigens, suggesting that IA4 is a differentiation mar
ker for macrophages, whatever the culture conditions, either adherent
(plastic culture dishes) or nonadherent (Teflon culture bags). IA4 sta
ble transfectants of the murine mastocytoma cell line P815 were obtain
ed and used to generate a new mAb. Competitive epitope binding studies
have shown that IA4 antigen presents a dominant epitope recognized by
most of the mAb prepared either in our lab or elsewhere. This dominan
t epitope is not shared by any of the other antigens of the TST family
. Using this new mAb we were able to biochemically characterize the IA
4 antigen as a 28-kDa protein, highly N-glycosylated with different pa
tterns on various cells. (C) 1994 Academic Press, Inc.