A comprehensive evaluation of murine and human ex vivo cultured alveolar macrophages

Alveolar macrophages (AMs) serve as the frontline defence in the lungs; however, comprehensive cell culture models for their study remain limited. Freshly isolated AMs are hindered by restricted quantities (mice) or challenges in accessing donors (humans). Recently, murine fetal liver-derived macrophages cultured with granulocyte-macrophages colony-stimulating factor were proposed as AMs-like macrophage (called MPI). Furthermore, recent technical progress improved the culture and expansion of primary murine AMs.

We examined three distinct in vitro models of alveolar macrophages: MPI, long-term culture-expanded AMs from mice (mAM) and cultured from human (hAM), aiming to compare and elucidate their respective advantages.

We observed that: 1) isolated AMs from mice and humans can be cultured for several days (human) or months (mice) with minor loss of AM-specific surface markers expression over time; 2) MPI is a self-replicative macrophage model that is easy to culture but lacks the typical AM surface expression marker (i.e. SiglecF) and presents a constitutive pro-inflammatory phenotype; 3) responses to Toll-like receptor (TLR) agonists are consistent between MPI, mAM and hAM models but differences in magnitude should be considered; 4) phagocytic activity of MPI, mAM and hAM were similar; 5) major differences were observed between murine and human AMs regarding programmed cell death, especially for MPI; and 6) ecological and ethical consequences of these AM models are different and sometimes opposed and should be carefully assessed.

Our study provides a comprehensive comparison of ex vivo murine and human AM models and gives insight into the translational value of these different AM models.