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The primary in vitro plaque forming cell (PFC) response of mouse (C57BL/6J) spleen cells to sheep red blood cells (SRBC) was inhibited by two sources of crude and two sources of partially purified mouse interferon. The substance(s) in the interferon preparations which induced PFC and antiviral inhibitory activity have the following common characteristics: a) The interferon preparations were of different potencies and specific activities, but they inhibited the PFC response in proportion to their activities; 20 to 60 units were the minimal amounts required for greater than 90% inhibition of the PFC response. b) Both the antiviral activity and the PFC inhibitory activity of the interferons were neutralized by antibody specific for mouse interferon. c) Both activities were partially or completely inactivated by heating at 60 degrees C for 1 h. d) Human interferons had neither antiviral activity nor PFC inhibitory activity in mouse cells. e) Limited exposure (4 h) of cells to interferon significantly inhibits both viral infection and the PFC response. f) Both the antiviral activity and the PFC inhibitory activity of the interferon preparations are acid stable. It is concluded, therefore, that the inhibition of the primary in vitro PFC response is due to interferon in the preparations. Maximum inhibition of the PFC response occurred when interferon was added to cultured at the same time as SRBC. Significant inhibition was also observed when interferon was added 1 day later, and slight enhancement was observed when added at days 2 and 3 of SRBC addition. Kinetic data showed that the greater the concentration of interferon added to the cultures, the earlier the effect on the PFC response. The presence of interferon in cultures for the first 4 h is sufficient to inhibit the PFC response. Interferon, then, appears to affect some early event(s), which leads to inhibition of the PFC response. Since mature T cells can be one of the sources of interferon, we have demonstrated a suppressor effect of a T cell lymphokine. The precise relationship of interferon to various expressions of suppressor T cell effects remains to be determined.
Johnson et al. (Wed,) studied this question.