Effects of intradermally administered plasmid deoxyribonucleic acid on ovine popliteal lymph node morphology.

In the last decade it has become apparent that bacterial deoxyribonucleic acid (DNA) is recognized as a "danger signal" by the mammalian immune system. To investigate this interaction, sheep were injected intradermally two centimeters distal to the lateral prominence of the fibular head with 400 microg of purified plasmid DNA. Over a 28-day period ultrasound measurements indicated a progressive increase in size of both plasmid and saline (controls) treated popliteal lymph nodes and at Day 30 macroscopic and histological measurements of the lymph nodes were determined. Compared with the contralateral control lymph nodes, plasmid exposed lymph nodes were heavier (2.8 +/- 0.1g vs. 2.0 +/- 0.6 g) and displayed prominent histological changes in the cortex and medulla. Average medullary cord thickness (114.2 +/- 25.2 microm) and the average distance across medullary sinuses (64.4 +/- 2.5 microm) were significantly greater after plasmid exposure relative to contralateral controls (62.7 +/- 14.9 microm and 36.5 +/- 1.0 microm, respectively). Total number of germinal centers (71.4 +/- 17.7) and the total area of germinal centers (4.0 +/- 1.3 mm(2)) within the cortex of popliteal lymph nodes exposed to plasmid were also significantly greater than the controls (40.4 +/- 11.4 and 1.6 +/- 0.5 mm(2), respectively). Our results demonstrate that a single exposure to plasmid DNA has long term effects on regional lymph node weight and morphology. Copyright 2001 Wiley-Liss, Inc.