Thymic humoral factor

Thymic factors are naturally occurring substances that promote T-lymphocyte differentiation and differentiation of early stem cells into prothymocytes. Each of the available preparations (e.g., thymic humoral factor, thymosin fraction 5, and thymodulin) are mixtures of several polypeptides isolated from a calf thymus extract. 

Indeed, levamisole is now thought to be cleaved in vivo to yield dl-2-0X0-3-(2-mercaptoethyl)-5-phenylimidazoline (60J, which was reported to be more potent than the parent compound in enhancing carbon clearance in mice . Recent evidence concurs to indicate that both levamisole and thymic factors (Trainin s thymic humoral factor and G. Goldstein s thymopoietin) have similar effects on cAMP and cGMP in lymphomyeloid target cells increase of cAMP in precursor populations, increase of cGMP in mature effector cells. In view of the apparent similarities of the in vivo... 

The isolation of thymic humoral factor (THF) by Trainin and colleagues was the culmination of studies to explain their observation that thymus tissue... 

Thymic hormones (TH), thymusfactors, hormones most likely produced in the thymus epithelium that participate in development of the lymphoid system and maturation of the ceUular immune response. Members of the TH are, for example, thymopoietin, thymosins, thymulin, thy-mopentin and the thymic humoral factor, a polypeptide with Mr 3.2 kDa [J.-F. Bach, in Thymic Factor Therapy, N. A. Byrom, J. R. Hobbes (Eds.), Vol. 16, p. 21 Raven Press, New York, 1984 T. L. Low, Thymus 1990, 15, 93). 

Activated helper T cells are also a source of immunoreactive Met-enkephalins. Up to 0.5% of mRNA in T cells encodes pre-proenkephalin so that enkephalins may behave as cytokines [143]. The immunoregulatory peptide, thymic humoral factor 2 (THF) augments T cell function which leads to increased production of interleukin-2 (IL-2) [144]. THF is an octapeptide Leu-Glu-Asp-Gly-Pro-Lys-Phe- Leu, and is inactivated by enkephalinase which hydrolyses the Lys -Phe bond. The immunomodula-tor effects of THF have been utilized in clinical conditions associated with impaired immune response. 

Dieter, M. P., 1971, Further studies on the relationship between vitamin C and thymic humoral factor, Proc. Soc. Exp. Biol. Med. 136 316. 

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