Low molecular mass inhibitors from calf thymus selective for T-lymphocyte proliferation

Endogenous factors preferentially inhibiting T-lymphocyte proliferation were prepared from the acetone precipitate of a 60% ethanol extract from calf thymus and their biochemical properties examined. By ultrafiltration the strongest lymphocyte-selective inhibition was found in the molecular mass range between 1 and 5 kDa. Fast protein liquid chromatography (FPLC) of this fraction on an anion exchange column eluted the lymphocyte inhibitors at 205-265 mM ammonium acetate. Staining procedures following IEF and TLC suggested, that the inhibitors may not be glycoconjugates or amines but small weakly acidic peptides (less than 3 kDa).