Arteriovenous shunting in the lymph node before and after antigenic stimulus.

We have assessed the effects of antigenic stimulation on the regional blood flow of the lymph node. In seventeen New Zealand white rabbits, the regional blood flow to the popliteal lymph nodes was determined using 9 and 15 micron microspheres at 16, 40, and 144 h following antigen administration. The regional blood flow in the resting lymph node measured with 15 micron spheres was 0 . 46 +/- 0 . 07 ml g-1 min-1, with 9 micron spheres 0 . 26 +/- 0 . 03 ml g-1 min-1. There was a significant 'differential flow' (the difference in blood flow between the experimental and control nodes) measured with 15 micron spheres (P less than 0 . 05). This increase in blood flow was larger early (16 h) than late (144 h) following antigen administration (P less than 0 . 01). There was significant (P less than 0 . 05) 'shunt flow' (the difference in blood flow measured with 15 micron and 9 micron spheres) in the lymph node, with more shunting early (16 h) than late (144 h) following antigen administration. No significant shunting was seen in the kidney or thigh muscle. Thus, we have established: (1) a significant increase in blood flow following antigenic stimulus; (2) shunting of 9 micron microspheres in the resting popliteal lymph node; (3) increased shunting following antigenic stimulus; and (4) that the increase in nodal blood flow was, to a large extent, secondary to increased shunt flow. Both the increased blood flow and the shunting shortly after antigenic stimulus may be important in the evolution of the immune response.