Highly concentrated urine-purified Tac peptide fails to inhibit IL-2-dependent cell proliferation in vitro.
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.
Pizzolo
G
G
Cattedra di Ematologia, Istituto di Patologia Generale, Verona, Italy.
Vincenzi
C
C
Vinante
F
F
Rigo
A
A
Veneri
D
D
Chilosi
M
M
Dusi
S
S
Poli
G
G
Zambello
R
R
Semenzato
G
G
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
D007376:Interleukin-2; D015375:Receptors, Interleukin-2