We describe here a mAb, DATK44, which induces homotypic aggregation of
TK1 cells (a CD8 lymphoma). The glycoprotein recognized by DATK44 is
of approximate m.w. 50 kDa and is expressed by monocytes, neutrophils,
and subsets of lymphocytes, as well as on the high endothelial venule
in peripheral and mesenteric lymph nodes. We named this Ag TABS (T ce
ll activation B cell subset Ag), as TABS appears on T lymphocyte activ
ation and is expressed at low and high levels by B cells. TABS is diff
erentially regulated during T lymphocyte development, CD4(+ve)CD8(+ve)
thymocytes being TABS(high), while single positive CD4(+ve) and CD8(ve) thymocytes are TABS(dull) CD4(-ve)CD8(-ve) thymocytes are clearly
split into dull and bright populations by the mAb. On exit from the th
ymus, T lymphocytes cease to express TABS, but T lymphocyte activation
results in re-expression of TABS. TABS also shows tight coregulation
with heat stable Ag on resting lymphocytes, but coexpression of these
two molecules is lost upon lymphocyte activation. DATK44-induced aggre
gation of TK1 cells is temperature sensitive and blocked by pretreatme
nt of the cells with metabolic inhibitors, genestein, dibutyl cAMP or
cytochalasin B, while colchicine, staurosporin, sphingosine, okadaic a
cid, and W7 are without effect. DATK44-induced TK1 cell aggregation ap
pears to be mediated by the LFA-1 pathway, as aggregation is blocked b
y anti-LFA-1 and anti-ICAM-1 mAbs but not by Abs capable of blocking C
D44 and alpha(4) beta(7)-mediated adhesion. Thus, TABS appears to be a
n adhesion inducer that selectively activates LFA-1-mediated lymphocyt
e aggregation.