The study shows that thymosin‑alpha‑1 (TM‑α1) can bind to the same surface receptor on human T‑cells as cholera toxin B‑subunit, and this binding boosts the activity of soluble guanylate cyclase (sGC), an enzyme linked to nitric‑oxide signaling. The effect is seen at very low (nanomolar) concentrations, suggesting a potent interaction, but the work is done in isolated cells, not in living people.

In this work, ¹²⁵I-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_d = 3.3 nM) was determined. The binding of the ¹²⁵I-labeled CT-B was inhibited by unlabeled interferon-α₂ (IFN-α₂), thymosin-α₁ (TM-α₁), and by the synthetic peptide LKEKK, which corresponds to sequences 16-20 of human TM-α₁ and 131-135 of IFN-α₂ (K_i 0.8, 1.2, and 1.6 nM, respectively), but was not inhibited by the unlabeled synthetic peptide KKEKL with inverted sequence (K_i > 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.