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

In the last decade it has become apparent that bacterial deoxyribonucleic a cid (DNA) is recognized as a "danger signal" by the mammalian immune system . To investigate this interaction, sheep were injected intradermally two ce ntimeters distal to the lateral prominence of the fibular head with 400 mug of purified plasmid DNA. Over a 28-day period ultrasound measurements indi cated a progressive increase in size of both plasmid and saline (controls) treated popliteal lymph nodes and at Day 30 macroscopic and histological me asurements of the lymph nodes were determined. Compared with the contralate ral 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 mum) and the average distance across medullary sinuses (64.4 +/- 2.5 mum) were s ignificantly greater after plasmid exposure relative to contralateral contr ols (62.7 +/- 14.9 mum and 36.5 +/- 1.0 mum, 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 pla smid 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 expo sure to plasmid DNA has long term effects on regional lymph node weight and morphology. Anat Rec 262:186-192, 2001. (C) 2001 Wiley-Liss, Inc.