Evidence That TGF-β Can Inhibit Human T-Lymphocyte Proliferation through Paracrine and Autocrine Mechanisms

Transforming growth factor-β (TGF-β) has been documented as having an inhibitory effect on the proliferation and growth of human T-lymphocytes. We examined the relative contribution of both exogenous and endogenous TGF-β to this inhibitory action. Purified human peripheral blood T-cells were cultured with Con A (0.2 μg/ml), washed with methyl mannopyranoside, and then cultured in rIL-2 (5 U/ml) with or without TGF-β (80 pM). Proliferation, as measured by uptake of tritiated thymidine at 72 hr, was inhibited by added active TGF-β. Addition of neutralizing anti-TGF-β antibodies at the initiation of culture abrogated the antiproliferative effects of TGF-β. A mink lung cell bioassay was used to measure endogenous TGF-β production by the T-cells following transient acidification of the supernatants to activate latent TGF-β. T-lymphocytes cultured with rIL-2 alone produced low levels of TGF-β, first detectable at 72 hr. The addition of (active) TGF-β to these cultures resulted in earlier and higher levels of endogenously produced latent TGF-β protein. This was reflected at the mRNA level as well. The exogenously added active TGF-β appeared to be depleted during the culture period, presumably by the activated T-cells, which exhibited elevated levels of types I, II, and Ill TGF-β receptors. The increase in TGF-β protein levels was due to endogenous TGF-β synthesis and secretion as supported by a capture assay using 35 S-labeled culture supernatants. These findings indicate that both paracrine and autocrine mechanisms are involved in the inhibitory effects of TGF-β on the proliferation of normal human T-lymphocytes and suggest that other TGF-β-producing cells can augment production of TGF-β by activated T-lymphocytes.