Natural cysteine proteinase inhibitors reduce lectin induced lymphocyte stimulation

Lymphocyte stimulation by lectins can be inhibited by several synthetic inhibitors of proteolytic enzymes, notably those of cysteine proteinases. The effects of naturally occurring enzyme inhibitors are less well known. The effect of the neutral low-molecular weight cysteine proteinase inhibitor (NCPI) recently purified from lymph nodes and spleen was therefore investigated. Cultured peripheral blood lymphocytes were stimulated by PHA or ConA in the presence or absence of NCPI and the incorporation of 3H-thymidine was measured. NCPI was found to inhibit these lymphocyte responses in these circumstances.