TGF-beta1 in SP-A preparations influence immune suppressive properties of SP-A on human CD4+ T lymphocytes.
Surfactant protein A (SP-A) and transforming growth factor-beta1 (TGF-beta1) have been shown to modulate the functions of different immune cells and specifically to inhibit T lymphocyte proliferation. The aim of the present study was to elucidate whether the Smad signaling pathway, which is activated by TGF-beta1, also plays a role in SP-A-mediated inhibition of CD4+ T lymphocyte activation. Recombinant human SP-A1 expressed in Chinese hamster ovary cells [rSP-A1m (mammalian)], but not recombinant Baculovirus-derived rSP-A1hyp (hydroxyproline-deficient), suppressed T lymphocyte proliferation and IL-2 mRNA expression. To test whether SP-A induced Smad signaling, a Smad3/4-specific reporter gene was transfected in primary human CD4+ T lymphocytes. Only rSP-A1m, but not rSP-A1hyp, induced Smad-specific reporter genes, Smad2 phosphorylation, and Smad7 mRNA expression. The effect of rSP-A1m was mediated through the TGF-betaRII and could be antagonized by anti-TGF-beta1 neutralizing antibodies and sTGF-betaRII. Western blot and ELISA analysis revealed that rSP-A1m, but not rSP-A1hyp, contained TGF-beta1. TGF-beta1 was responsible for the differences in inhibition of CD4+ T lymphocyte proliferation and activation of the Smad signaling pathway between rSP-A1m and rSP-A1hyp. After acidification, native SP-A, obtained from patients with alveolar proteinosis, also induced Smad signaling in human CD4+ T lymphocytes leading to an increased inhibition of T lymphocyte proliferation, thus indicating the presence of inactive, latent TGF-beta1 in native SP-A samples. Association between SP-A and latent TGF-beta1 provides a possible novel mechanism to regulate TGF-beta1-mediated inflammation and fibrosis reactions in the lung but also leads to possible misinterpretation of immune-modulator functions of SP-A. Monitoring of SP-A preparations for possible TGF-beta1 is essential.
Kunzmann
Steffen
S
University Children's Hospital, Josef-Schneider-Strasse 2, 97080 Würzburg, Germany. Kunzmann_s@kinderklinik.uni-wuerzburg.de
Wright
Jo Rae
JR
Steinhilber
Wolfram
W
Kramer
Boris W
BW
Blaser
Kurt
K
Speer
Christian P
CP
Schmidt-Weber
Carsten
C
D000143:Acids / Q000494:pharmacology; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D016466:CHO Cells; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D037662:Pulmonary Surfactant-Associated Protein A / Q000737:chemistry* / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000737:chemistry / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D051785:Smad Proteins / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000032:analysis* / Q000494:pharmacology*; D053773:Transforming Growth Factor beta1
D000143:Acids; D007166:Immunosuppressive Agents; D037662:Pulmonary Surfactant-Associated Protein A; D011994:Recombinant Proteins; D051785:Smad Proteins; C508960:TGFB1 protein, human; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1