In vivo visualization of lymphatic microvessels and lymphocyte migration through rat Peyer's patches

In the small intestine, lymphocytes migrate through Peyer's patches. The distribution of lymphatic microvessels in rat Peyer's patches and lymphocyte traffic through them were studied.

Vital dyes were injected via a micropipette into the Peyer's patches tissue to fill lymphatic microvessels and to stain lymphocytes in lymphatic microvessels.

Direct microscopic observation revealed a dense plexus of lymphatic microvessels in the perifollicular and interfollicular areas. Injection of the dyes into the germinal center failed to delineate lymphatic microvessels. The lymphatic microvessels in the perifollicular area were filled with lymphocytes. Most lymphocytes in the perifollicular lymphatics stayed in the lymphatic microvessels. Some lymphocytes became detached and drained into lymphatic microvessels in the interfollicular areas. Lymphocytes then moved toward the submucosal lymphatics beneath the villi around the Peyer's patches. The interfollicular lymphatics did not display contractile activity but had valves. Opening and closing of valves was synchronized with the respiration and the back and forth flow of lymphocytes.

There are numerous lymphocytes in a dense lymphatic network in the perifollicular and interfollicular areas of Peyer's patches. This well-developed lymphatic network has the potential capacity for storage of lymphocytes and modulation of lymphocyte migration.