CCL3 and bronchopulmonary dysplasia: In addition, we observed a heightened chemotactic response of macrophages from BPD rats toward CCL3, suggesting that enhanced macrophage numbers in BPD-affected lungs are a consequence of increased recruitment of monocytes from the circulation, since there is little proliferation within the lung41, although there is a possibility that the increased lung macrophages in BPD were transformed from resident alveolar macrophages (rAMs).