TGF-beta1 in SP-A preparations influences immune suppressive properties of SP-A on human CD4+ T lymphocytes

Kunzmann S, Wright JR, Steinhilber W, Kramer BW, Blaser K, Speer CP, Schmidt-Weber C
Source: Am J Physiol Lung Cell Mol Physiol
Publication Date: (2006)
Issue: 291(4): L747-56
Research Area:
Immunotherapy / Hematology
Cells used in publication:
T cell, human peripheral blood unstim.
Species: human
Tissue Origin: blood
T cell, human stim.
Species: human
Tissue Origin: blood
Nucleofector® I/II/2b
Surfactant protein A (SP-A) and transforming growth factor-beta(1) (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-A1(hyp) (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-A1(hyp), 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-A1(hyp), 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-A1(hyp). 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.