Production of transforming growth factor beta by human T lymphocytes and its potential role in the regulation of T cell growth

This study examines the potential role of transforming growth factor beta (TGF-beta) in the regulation of human T lymphocyte proliferation, and proposes that TGF-beta is an important autoregulatory lymphokine that limits T lymphocyte clonal expansion, and that TGF-beta production by T lymphocytes is important in T cell interactions with other cell types. TGF-beta was shown to inhibit IL-2-dependent T cell proliferation. The addition of picograms amounts of TGF-beta to cultures of IL-2-stimulated human T lymphocytes suppressed DNA synthesis by 60-80%. A potential mechanism of this inhibition was found. TGF-beta inhibited IL-2-induced upregulation of the IL-2 and transferrin receptors. Specific high-affinity receptors for TGF-beta were found both on resting and activated T cells. Cellular activation was shown to result in a five- to sixfold increase in the number of TGF-beta receptors on a per cell basis, without a change in the affinity of the receptor. Finally, the observations that activated T cells produce TGF-beta mRNA and that TGF-beta biologic activity is present in supernatants conditioned by activated T cells is strong evidence that T cells themselves are a source of TGF-beta. Resting T cells were found to have low to undetectable levels of TGF-beta mRNA, while PHA activation resulted in a rapid increase in TGF-beta mRNA levels (within 2 h). Both T4 and T8 lymphocytes were found to make mRNA for TGF-beta upon activation. Using both a soft agar assay and a competitive binding assay, TGF-beta biologic activity was found in supernatants conditioned by T cells; T cell activation resulted in a 10-50-fold increase in TGF-beta production. Thus, TGF-beta may be an important antigen-nonspecific regulator of human T cell proliferation, and important in T cell interaction with other cell types whose cellular functions are modulated by TGF-beta.

A potential role for adrenocorticotropin in regulating human B lymphocyte functions

Adrenocorticotropin (ACTH) was found to enhance the growth and differentiation of human B lymphocytes. By using highly purified preparations of human tonsillar B cells, the effects of ACTH on the growth and differentiation of in vitro activated B cells were examined. Optimal concentrations of ACTH were found to increase the proliferation of activated B cells by twofold to threefold when ACTH was present in culture with either a B cell growth factor or recombinant interleukin 2 (IL 2). ACTH had essentially no effects when added to cultures of activated B cells in the absence of the growth factor. Additionally, when ACTH was added in conjunction with an optimal concentration of either a B cell differentiation factor or IL 2 to cultures of activated B cells, the combination of ACTH and factor enhanced Ig secretion by twofold compared with the factor alone. In the absence of the differentiative signal, ACTH had minimal effects on Ig production. Only the first 24 amino acid fragments of ACTH were required to enhance B cell growth and differentiation when combined with the appropriate, more classical signals. Thus, ACTH may have a physiologic role in regulating human B cell function.

A potential role for adrenocorticotropin in regulating human B lymphocyte functions

Adrenocorticotropin (ACTH) was found to enhance the growth and differentiation of human B lymphocytes. By using highly purified preparations of human tonsillar B cells, the effects of ACTH on the growth and differentiation of in vitro activated B cells were examined. Optimal concentrations of ACTH were found to increase the proliferation of activated B cells by twofold to threefold when ACTH was present in culture with either a B cell growth factor or recombinant interleukin 2 (IL 2). ACTH had essentially no effects when added to cultures of activated B cells in the absence of the growth factor. Additionally, when ACTH was added in conjunction with an optimal concentration of either a B cell differentiation factor or IL 2 to cultures of activated B cells, the combination of ACTH and factor enhanced Ig secretion by twofold compared with the factor alone. In the absence of the differentiative signal, ACTH had minimal effects on Ig production. Only the first 24 amino acid fragments of ACTH were required to enhance B cell growth and differentiation when combined with the appropriate, more classical signals. Thus, ACTH may have a physiologic role in regulating human B cell function.