Characterization of scavenger receptor activity in resident human lung macrophages

We characterized scavenger receptor pathways of human alveolar macrophages and cultured monocytes using radiolabeled maleylated bovine serum albumin (MAL-BSA) and acetylated low-density lipoprotein (Ac-LDL) as ligands. Human alveolar macrophages and cultured human monocytes degraded both MAL-BSA and Ac-LDL. Both ligands were bound and degraded in a specific and saturable fashion. Specificity of degradation was tested using excess MAL-BSA and Ac-LDL, polyanionic compounds, and alpha-casein as inhibitors. Alveolar macrophages utilized the classical scavenger receptor pathway to degrade MAL-BSA and Ac-LDL. In contrast, cultured monocytes utilized two receptor pathways to degrade MAL-BSA: the classical scavenger receptor pathway and a secondary alpha-casein-inhibitable pathway. These results demonstrate differences in the activities of receptor systems in cultured monocytes compared to alveolar macrophages.