Immunosuppressive effect of vasoactive peptides derived from human fibrinogen

Abstract Various products obtained after plasmin-mediated lysis of fibrinogen were examined for their effect on 3 H-TdR uptake in mitogen-stimulated murine lymphocytes. A crude mixture of low molecular weight fibrinogen degradation products inhibited the 3 H-TdR uptake more strongly after stimulation of the lymphocytes by lipopolysacharide (LPS) than by Con A. This effect was at least partly due to a lower degree of stimulation by LPS. Fraction 6 out of ten fractions obtained at molecular sieve chromatography on Bio-Gel P-6 had the strongest action. Two peptides which had been previously isolated from this fraction (peptide 6A: Ala-Arg-Pro-Ala-Lys, and peptide 6D: Ser-Gln-Leu-Gln-Lys-Val-Pro-Pro-Glu-Trp-Lys) were probably largely responsible for this inhibition. Neither fraction 6 nor the two peptides exhibited any cytotoxic effect, determined as 86 Rb release, which could explain the findings. It is possible that both peptides have immunosuppressive properties in vivo also.