Activity of pulmonary intravascular macrophages in cats and dogs with and without adult Dirofilaria immitis

Pulmonary intravascular macrophages (PIMs). large (20-80 mu m diameter) monocytes are present in sheep, pigs. and horses. but not ill dogs. rats. rabbits. or primates. The present study evaluated the phagocytic activity of various organs ill cats and dogs and determined the influence of Dirofilaria immitis infections oil PIM activity. Live or dead adult heartworm (HW) was transplanted via jugular venotomy into cats and Cats (four per group) were allocated to live groups: surgical controls-no HW. dead HW for 1 week. live HW for I week. dead HW for 3 weeks. or live HW for 3 weeks. Radioactive technetium (Tc-99m. 1.2 mCi in 0.3 ml) sulfa-colloid was injected intravenously. All cats with HW were clinically asymptomatic and developed radiographic pulmonary parenchymal changes. No gross changes were visible at necropsy for cats with HW: inflammatory changes were less severe in cats with live HW. In cats with dead HW for 3 weeks. worms were present but folded, flattened. and located ill distal pulmonary arteries. Uninfected control dogs and those with dead HW did not demonstrate ally PIM activity. In Control Cats, lungs were the primary phagocytic organ after systemic IV colloid injection (72.5% of the total recovered radioactive dose). The lung and liver together represented over 95% of the recovered Tc-99m colloid in all cats. In each group of cats with HW, phagocytic activity of the lung Was significantly less (p < 0.001) than the PIM activity of controls. Cats with dead HW at 1 week (50.1%) had a significant (p < 0.019) decrease ill PIM activity compared with cats with dead HW at 3 weeks (59.5%). The PIM activity in cats with live HW was Significantly decreased (p < 0.001) from that in groups with dead HW, but there was no significant difference between the two group infected with live worms. There were no significant differences in recovery between any groups)S in pairwise analysis of the spleen. heart, skeletal muscle. kidney. hone marrow, or blood. Significant increases (p < 0.001) in liver activity, for each group) inversely reflected the decreased lung activity: consistent with increased hepatic Uptake of Tc colloid escaping a relatively suppressed lung rnacrophage system. Transmission electron microscopy confirmed PIM glycocalyx changes and vacuolization, Type I cell damage and Type II cell hypertrophy in cats with dead HW. There was no evidence of PIM death. The significant decrease in PIM activity in groups with dead HW and a greater decrease in groups with live HW are consistent with a down-regulation of PIM function in cats with live HW. (C) 2008 Elsevier B.V. All rights reserved.