title: Alleviation of immunosuppression in vitro by recombinant platelet factor 4.
abstract: To elucidate the mechanism by which platelet factor 4 (PF4), a secreted platelet protein, and its C-terminal peptides alleviate suppression of the antibody response in vivo, their immunoregulatory activity was studied in vitro, using cultured spleen cells from BALB/c mice primed with sheep red blood cells (SRBC). When addition of 48 h cultured concanavalin A (Con A) blasts at 5 x 10(5)/ml significantly suppressed the anti-SRBC plaque-forming cell response, suppression was alleviated in 25 of 29 experiments by 0.2 micrograms/ml recombinant (r)PF4 (6.4 nM if rPF4 is a tetramer). The effect of Con A blasts was abolished by cimetidine, a histamine type 2 (H2) antagonist. Dimaprit, an H2 agonist, at 1-2 x 10(-4) M, or splenic T cells that had been incubated for 1 h with dimaprit and washed, also caused significant suppression that was alleviated by 0.2 micrograms/ml rPF4 (n = 8), and by 0.02 micrograms/ml in six of these tests. The C-terminal 13 amino acid peptide of PF4 was active at 0.02-0.2 micrograms/ml (0.01-0.11 microM), but peptides from the middle or N-terminal end of the molecule, or IL-8, which shares structural homology with PF4, were inactive. IL-1 and IL-2 raised control responses without affecting suppression or its alleviation by rPF4. Neutralizing antibody to transforming growth factor beta 1 (TGF-beta 1) did not affect Con A blast-induced suppression and suppression induced by exogenous TGF-beta 1 (0.5 ng/ml) was not counteracted by rPF4. Blocking prostaglandin production with 0.2 or 2 microM indomethacin did not affect suppression significantly but reduced rPF4 activity; prostaglandin D2 restored the effect of rPF4.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pathology, New York University Medical Center, New York 10016.
authors.forename: I R
authors.initials: IR
authors.lastname: Katz
authors.forename: G J
authors.initials: GJ
authors.lastname: Thorbecke
authors.forename: M B
authors.initials: MB
authors.lastname: Zucker
mesh_terms: D000818:Animals; D002927:Cimetidine / Q000494:pharmacology; D003208:Concanavalin A; D017259:Dimaprit; D004306:Dose-Response Relationship, Immunologic; D007108:Immune Tolerance / Q000187:drug effects / Q000276:immunology*; D066298:In Vitro Techniques; D007213:Indomethacin / Q000494:pharmacology; D007375:Interleukin-1 / Q000276:immunology; D007376:Interleukin-2 / Q000276:immunology; D016209:Interleukin-8 / Q000276:immunology; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D010978:Platelet Factor 4 / Q000494:pharmacology*; D011453:Prostaglandins / Q000502:physiology; D011970:Receptors, Histamine H2; D011994:Recombinant Proteins / Q000494:pharmacology; D013890:Thiourea / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000276:immunology
chemical_list: D007375:Interleukin-1; D007376:Interleukin-2; D016209:Interleukin-8; D011453:Prostaglandins; D011970:Receptors, Histamine H2; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D003208:Concanavalin A; D010978:Platelet Factor 4; D002927:Cimetidine; D013890:Thiourea; D007213:Indomethacin; D017259:Dimaprit