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Last week (#95) we discussed how the capillary bed of the terminal lung alveoli – where the RBCs receive O2 and give up CO2 – gets ‘first dibs’ on newly minted immune effector cells and antibodies. The oxygenated blood then returns to the right side of the heart via the pulmonary veins to be pumped around the body via the much more powerful left ventricle. As with every other tissue, the lung must access oxygenated blood that comes in at about six times the pressure (of the pulmonary artery supply #95) via the bronchial arteries. These blood vessels travel with, and branch with, the lung bronchi, to end finally in the capillaries and post-capillary venules, where most extravasation of molecules (like circulating Igs #19, #20, #21) and recently stimulated, ‘activated’ B and T lymphocytes is likely to occur (#94). As this happens, every region of the lung that is supporting virus replication can now be a site of acute damage by incoming CD8+ killer T cells as they eliminate the virus-producing ‘factory’ cells. Obviously the more effectively that vaccination limits the extent of earlier virus dissemination, the better our lung function will be.