C. Francois et al., IMMUNOLOGICAL CHARACTERIZATION OF ANTIGENIC DOMAINS ON HUMAN IL-2 RECEPTOR-BETA SUBUNIT - EPITOPE-FUNCTION RELATIONSHIPS, International immunology, 7(8), 1995, pp. 1173-1181
Five mAb directed at the IL-2R beta chain were analyzed for their bind
ing and functional properties. They define three epitopes on a recombi
nant soluble beta chain or on the beta chain expressed at the surface
of YT-2C2 cells. Epitope 1 (A41 and 6E8 mAb) is part of the IL-2 bindi
ng domain, whereas epitope 2 (CF1 and 6E10 mAb) is not involved in IL-
2 binding. Epitope 3 (6B5 mAb) also partly overlaps the IL-2 binding d
omain but does not overlap epitopes 1 and 2. None of the mAb can by th
emselves inhibit IL-2 induced proliferation of a human activated T cel
l clone. Only epitope 1 mAb can synergize with an anti-alpha chain mAb
to inhibit this proliferation. Using epitope 1 and 2 mAb as well as a
purified, recombinant form of the IL-2R beta chain extracellular doma
in, an ELISA-based immunoassay was set up which allows the quantitativ
e determination of soluble and detergent solubilized IL-2R beta chains
. Epitopes 1 and 2 are in non-competitive interaction: the binding of
a mAb to one epitope decreases the affinity of a mAb for the second ep
itope. Epitope 2 mAb have binding stoichiometries (-16,000 sites/cell)
which are -80% higher than that of epitope 1 mAb and IL-2 itself (-90
00 sites/cell), Upon binding of epitope 2 mAb, the stoichiometries of
epitope 1 mAb and IL-2 are increased to reach the stoichiometry of epi
tope 2 mAb, A molecular model is proposed in which the IL-2R beta chai
n exists in two different states on YT-2C2 cells: one associated with
the intermediate-affinity IL-2R ply complex, the other being part of a
receptor structure which is not accessible to epitope 1 mAb and IL-2.