lmmunobiol., vol. 195, pp. 314-322 (1996) <> 1996 by Gus tav Fischer Verlag, Stuttgart IInstitute for Medical Chemistry and Biochemistry, 2Institute for Hygiene, University of Innsbruck, Innsbruck, Austria, and 3Institute for Experimental Microbiology, Univer- sity of Jena, Jena, Germany Streptococcal Erythrogenic Toxins Induce Neopterin Formation in Human Peripheral Blood Mononuclear Cells but not in the Human Myelomonocytoma Cell Line THP-l CHRISTIAN MURRl, GABRIELE BAIER-BITTERLICH 1 , DIETMAR FUCHS!, DIETER GERLACH 3 , GABRIELE W ERNER-FELMAYER!, MANFRED P. DIERICH 2 , and HELMUT WACHTER l Received Mai 4, 1995 . Accepted in revised form January 9, 1996 Abstract We tested whether the exposure of human monocytic cells to streptococcal erythrogenic toxins A, B, C and a streptococcal-derived Mitogen BX is associated with synthesis of neopterin in vitro. Neopterin production was not induced when the human myelomono- cytoma cell line THP-1 was stimulated with these toxins, and there was only a slight co- stimulatory effect of streptococcal erythrogenic toxin A together with interferon-y stim- ulation. However, these toxins induced interferon-y and further neopterin production in peripheral blood mononuclear cells of three healthy individuals. This neopterin formation could be blocked by anti-human interferon-yo From our investigations we conclude that there is no direct effect of streptococcal erythrogenic toxins on neopterin production by monocytic cells. However, the data obtained in peripheral blood mononuclear cell culture imply that these toxins are able to stimulate neopterin production in humans via the in- duction of huge amounts of interferon-yo Abbreviations: ET = erythrogenic toxin; JL-2 = interleukin 2; I L-3 = interleukin 3; JL-6 = interleukin 6; TNF-a = tumor necrosis factor a; IFN-y= interferon-y, GTP = guanosine triphosphate; PBMC = peripheral blood mononuclear cells