Immunoregulatory macrophages modify local pulmonary immunity and ameliorate hypoxic-pulmonary hypertension

Macrophages play a central role in the onset and progression of vascular disease in pulmonary hypertension (PH) and cell-based immunotherapies aimed at treating vascular remodeling are lacking.

To evaluate the effect of pulmonary administration of macrophages modified to have an anti-inflammatory/pro-resolving phenotype in attenuating early pulmonary inflammation and progression of experimentally induced PH.

Mouse bone marrow derived macrophages (BMDMs) were polarized in vitro to a regulatory (M2 _reg ) phenotype. M2 _reg profile and anti-inflammatory capacity were assessed in vitro upon lipopolysaccharide (LPS)/interferon-γ (IFNγ) restimulation, before their administration to 8- to 12-week-old mice. M2 _reg protective effect was tested at early (2 to 4 days) and late (4 weeks) time points during hypoxia (8.5% O ₂ ) exposure. Levels of inflammatory markers were quantified in alveolar macrophages and whole lung, while PH development was ascertained by right ventricular systolic pressure (RSVP) and right ventricular hypertrophy (RVH) measurements. Bronchoalveolar lavage (BAL) from M2 _reg -transplanted hypoxic mice was collected, and its inflammatory potential tested on naïve BMDMs.

M2 _reg macrophages demonstrated a stable anti-inflammatory phenotype upon a subsequent pro-inflammatory stimulus by maintaining the expression of specific anti-inflammatory markers (Tgfß, Il10 and Cd206) and downregulating the induction of proinflammatory cytokines and surface molecules (Cd86, Il6 and Tnfα). A single dose of M2 _regs attenuated the hypoxic monocytic recruitment and perivascular inflammation. Early hypoxic lung and alveolar macrophage inflammation leading to PH development was significantly reduced and, importantly, M2 _regs attenuated RVH, RVSP and vascular remodeling at 4 weeks post treatment.

Adoptive transfer of M2 _regs halts the recruitment of monocytes and modifies the hypoxic lung microenvironment, potentially changing the immunoreactivity of recruited macrophages and restoring normal immune functionality of the lung. These findings provide new mechanistic insights on the diverse role of macrophage phenotype on lung vascular homeostasis that can be explored as novel therapeutic targets.