title: Highly concentrated urine-purified Tac peptide fails to inhibit IL-2-dependent cell proliferation in vitro.
abstract: Tac peptide, i.e., the p55 chain of the human interleukin-2 receptor (IL-2R) complex, is detectable as a soluble from (sIL-2R) in normal sera and, at increased levels, in patients with different diseases. Since several immunological abnormalities are observed in most conditions associated with an increase in sIL-2R levels, a down-regulatory effect on IL-2-dependent functions has been postulated as a consequence of binding and functional block of IL-2 by the excess of sIL-2R. To test this hypothesis, we purified sIL-2R from the urine of a patient with hairy cell leukemia and investigated the possible inhibitory effect of this peptide on the in vitro IL-2-induced cell proliferation. The urine-purified molecule was detectable by the specific immunoassay utilized to measure the serum Tac peptide and was constructed by a single polypeptide of about 50 kDa which was able to bind IL-2. Experiments performed with the IL-2-dependent murine CTLL-2 cell line and with PHA-stimulated human peripheral blood mononuclear cells showed that the purified sIL-2R at concentrations up to about 300 nM was unable to block IL-2-dependent cell proliferation. According to these data, which can be explained by the low affinity for IL-2 of the p55 IL-2R chain, it seems unlikely that in vivo the soluble Tac peptide can exert a down regulatory effect on IL-2-induced phenomena through a functional block of IL-2.
authors.affiliation: Cattedra di Ematologia, Istituto di Patologia Generale, Verona, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Pizzolo
authors.forename: C
authors.initials: C
authors.lastname: Vincenzi
authors.forename: F
authors.initials: F
authors.lastname: Vinante
authors.forename: A
authors.initials: A
authors.lastname: Rigo
authors.forename: D
authors.initials: D
authors.lastname: Veneri
authors.forename: M
authors.initials: M
authors.lastname: Chilosi
authors.forename: S
authors.initials: S
authors.lastname: Dusi
authors.forename: G
authors.initials: G
authors.lastname: Poli
authors.forename: R
authors.initials: R
authors.lastname: Zambello
authors.forename: G
authors.initials: G
authors.lastname: Semenzato
mesh_terms: D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line / Q000187:drug effects; D006801:Humans; D007376:Interleukin-2 / Q000037:antagonists & inhibitors*; D007943:Leukemia, Hairy Cell / Q000652:urine; D051379:Mice; D015375:Receptors, Interleukin-2 / Q000276:immunology* / Q000302:isolation & purification
chemical_list: D007376:Interleukin-2; D015375:Receptors, Interleukin-2