Table 1

Relative strength of antigens to interactions in solution and T cell contacts. The relative activities and classifications are based on the ability of these ligands to induce apoptosis, IL-2 production, or proliferation of T cells (4). Equilibrium and kinetic constants are given (4) by injections of soluble MHC molecules presenting the indicated covalently attached peptides over a TCR-coupled biosensor. The half-life (t 1/2) for a first-order decay process is (ln 2) ÷ k off. Cluster densities and total number of molecules are determined on images acquired at the same resolution for 3.L2 and 2B4 systems (original image element = 0.018 μm2). The 2B4 T cells have twofold as many TCRs as the 3.L2 T cells. Mean of >50 clusters for each point. Equilibrium and kinetic constants were not detected for the null ligands. ND, not determined; molec., molecule.

LigandRelative activityClassificationKA(mM−1)kon (M−1s−1)t1/2 (s)Density (molec./μm2)Total no. of molec.
Cytochrome system
MCC88-103100Agonist16.690012.1352770
T102S1Weak agonist4.21,5001.92193310
T102G<0.001Antagonist0.663,4000.145350
K99A0NullNDNDND<10<10
Hemoglobin system
Hb64-76100Agonist835,55710.8132407
N72T2Weak agonist10115,3745.10106203
N72I0.006Antagonist6715–25,000∼2.868120
N72A0.0007Weak antagonist<2.33492
N72E0NullNDNDND<10<10