Interaction of cholera toxin B subunit with T and B lymphocytes

We have prepared 125I-labeled cholera toxin B subunit (125I-labeled CT-B, a specific activity of 98Ci/mmol) and found that its binding to T and B lymphocytes from the blood of healthy donors was high-affinity (Kd 2.8 and 3.0nM, respectively). The binding of labeled protein was completely inhibited by unlabeled thymosin-α1 (TM-α1), interferon-α2 (IFN-α2), and the synthetic peptide LKEKK that corresponds to residues 16–20 in TM-α1 and 131–135 in IFN-α2, but was not inhibited by the synthetic peptide KKEKL with inverted amino acid sequence (Ki>10μM). Thus, TM-α1, IFN-α2, and the peptide: LKEKK bind with high affinity and specificity to CT-B receptor on donor blood T and B lymphocytes. It was found that CT-B and the peptide: LKEKK at concentrations of 10–1000nM increased in a dose-dependent manner the soluble guanylate cyclase activity in T and B lymphocytes. [Display omitted] •Cholera toxin B subunit binds with high affinity to human T and B lymphocytes.•TM-α1, INF-α2, peptide LKEKK completely inhibit the cholera toxin B subunit binding.•Residues 16–20 in TM-α1 and 131–135 in IFN-α2 are involved in binding to the receptor.•Binding to the receptor leads to an increase in activity of soluble guanylate cyclase.