Immortalized Porcine Alveolar Macrophages (3D4/21)

3D4/21 is a continuous, immortalized porcine alveolar macrophage (PAM) cell line derived from primary porcine alveolar macrophages. It provides a stable, reproducible, and readily expandable in vitro model that retains essential macrophage features, including adherent morphology, phagocytic activity, expression of macrophage-associated markers, and responsiveness to microbial stimulation with cytokine and chemokine secretion.

A key advantage of 3D4/21 cells is their susceptibility to porcine reproductive and respiratory syndrome virus (PRRSV). They express macrophage receptors relevant to PRRSV entry and support productive infection, making them a practical platform for viral isolation, propagation, titration, and mechanistic studies of virus–host interactions. They are also valuable for investigating innate immune signaling, inflammatory responses, and macrophage polarization in pigs, as well as for evaluating antiviral compounds, vaccine candidates, and immunomodulators. As a homogeneous line, they reduce variability associated with mixed primary PAM cultures and enable reproducible quantification of infection and immune responses. The line is compatible with common molecular and functional techniques, including transfection, RNA interference, CRISPR-based editing, flow cytometry, ELISA, and high-content imaging, facilitating drug screening and target validation.

Because immortalization can alter some phenotypic and functional properties, results should be validated against primary PAMs when physiological fidelity is critical. Overall, 3D4/21 cells combine macrophage-like biology with the convenience and scalability of a continuous cell line, offering a robust, ethically favorable, and cost-effective tool for swine respiratory disease research, immunology, and antiviral development.