Interaction of Cholera Toxin B-subunit with Human T-lymphocytes.

In this work, I-labeled cholera toxin B-subunit (CT-B) (specific activity 98 Ci/mmol) was prepared, and its high-affinity binding to human blood T-lymphocytes (K = 3.3 nM) was determined. The binding of the I-labeled CT-B was inhibited by unlabeled interferon-α (IFN-α), thymosin-α (TM-α), and by the synthetic peptide LKEKK, which corresponds to sequences 16-20 of human TM-α and 131-135 of IFN-α (K 0.8, 1.2, and 1.6 nM, respectively), but was not inhibited by the unlabeled synthetic peptide KKEKL with inverted sequence (K > 1 µM). In the concentration range of 10-1000 nM, both CT-B and peptide LKEKK dose-dependently increased the activity of soluble guanylate cyclase (sGC) but did not affect the activity of membrane-bound guanylate cyclase. The KKEKL peptide tested in parallel did not affect sGC activity. Thus, the CT-B and peptide LKEKK binding to a common receptor on the surface of T-lymphocytes leads to an increase in sGC activity.