Blood and lung level of antibody-enzyme conjugates of various sizes in vivo. A–C. Blood level and pulmonary uptake of anti-PECAM/catalase conjugates in PECAM KO mice (PECAM KO, black bars) vs wild type mice (WT, gray bars). D–F. Blood level and pulmonary uptake of control IgG/SOD (black bars) vs anti-PECAM/SOD (gray bars) conjugates. 125-I-labeled conjugates were injected IV, tissues were harvested in 1 h. A, 40 nm; B, 80 nm; C, 300 nm. D, 200 nm; E, 300 nm; F, 800 nm. * p<0.001 targeting vs. non-targeting conditions by t-test.