DNA-containing extracellular 50-nm particles in the ileal Peyer's patch of sheep

Follicles of the ileal Peyer's patch are sites of B cell proliferation and of diversification of the primary immunoglobulin repertoire in ruminants. We demonstrate here that 50-nm carbonic anhydrase-reactive particles released in the intercellular space in the follicle-associated epithelium of the ileal Peyer's patch of lambs contain DNA protected with a detergent-resistant membrane. We named these particles DiCAPs (DNA in carbonic anhydrase particles). DiCAPs can be purified from a suspension collected from ileal Peyer's patch follicles by sedimentation in a sucrose gradient. The DiCAP membrane is resistant to several ionic and non-ionic detergents alone, but can be disrupted by a combination of Triton X-100 and proteinase K. Differential nuclease treatment of purified DiCAPs indicates that they contain DNA. Digestion of DiCAP DNA with six-base pair restriction enzymes produces smears, suggesting that individual DiCAPs contain unique sequences. Nonetheless, the size of DiCAP DNA is smaller (approximately 16 kb) than that of lamb genomic DNA. Polymerase chain reaction and sequence analysis of DiCAP DNA reveals the presence of light and heavy chain variable genes as well as housekeeping genes. The data demonstrate the presence of DNA in these extracellular particles, and suggest a role of DiCAPs in transfer of DNA between cells within the ileal Peyer's patch. This raises the possibility of a novel form of communication between cells mediated by nucleic acids.