[Effect of a low-molecular humoral factor of the thymus gland on the lymphocyte sensitivity to phytohemagglutinin].

The preincubation of mouse spleen lymphocytes with a low molecular lymphocytosis-stimulating substance from the thymus (LSS), or the addition of the LSS to the cultures caused inhibition of the mitotic response of lymphocytes to phytohemagglutinin (PHA). LSS induced transformation of murine thymocytes to the blast cells capable of mitotic division. This transformation was depressed by PHA. The lymphocytes of the mice injected LSS in vivo responded weakly to PHA at first, but in 5 days a significant intensification on the response to PHA was observed. It is concluded that LSS may activate the T-cells responding to PHA.