Immune outposts in the adventitia: One foot in sea and one on shore

• Adventitial perivascular niches contain specialized stromal and immune cells.• Tissue-resident type 2 and regulatory lymphocytes are enriched in the adventitia.• Adventitia contain lymphatics, neurons, and fibroblast-like stromal cells.• Adventitial stromal cells are critical tissue immunomodulators.• Adventitial - immune crosstalk impacts tissue physiology and inflammatory response.