Changes induced in the lymphoid system by the double-stranded RNA.

Systemic (i.p.) single injection of ds RNA, an inducer of interferon, increases significantly the weight and cellularity of the lymphoid system. The peaks of increase are evident in peritoneal lymph nodes 24 h, in popliteal, axillary and inguinal lymph nodes 48 h, in the spleen and liver 72 h post-inoculation. Thymus weight and cellularity decrease markedly (with a minimum at 24 h) and the number of peritoneal cells also decreases. The parameters examined gradually return to normal values. Local injection of the same dose of ds RNA into the hind footpad results in a marked increase in the weight of the ipsilateral popliteal lymph node and, with some delay, in an increase in its cellularity. In addition, local injection has an effect on the other lymph nodes, the spleen and thymus, even though the effect is slighter than that of systemic injection. The mechanisms by which ds RNA induces changes in the lymphoid system are discussed.