Alternative Macrophage Activation Is Increased in Asthma.

Area of Science:

• Immunology
• Cell Biology
• Respiratory Medicine

Background:

• Type 2 T helper (Th2) cell responses are central to asthma pathogenesis.
• Alternatively activated (M2) macrophages are increasingly recognized for their role in Th2 immunity.
• The specific alterations and functions of M2 macrophages in asthma require further characterization.

Purpose of the Study:

• To investigate the phenotype and function of M2 macrophages in human subjects with asthma.
• To compare M2 macrophages from individuals with asthma to those from healthy controls.
• To explore the role of M2 macrophages in modulating immune cell interactions within the context of asthma.

Main Methods:

• Generation of monocyte-derived M2 macrophages in vitro using macrophage colony-stimulating factor and IL-4.
• Analysis of bronchoalveolar lavage fluid (BALF) macrophages from asthma patients and healthy volunteers.
• Flow cytometry and quantitative PCR were used to assess macrophage phenotype (CD206, MHC class II, histamine receptor 1, E-cadherin) and cytokine production (IL-6, IL-10, IL-12p40).
• In vitro assays examined the impact of M2 macrophages on dendritic and CD4+ T cell activation.

Main Results:

• M2 macrophages, identified by high CD206 and MHC class II expression, were significantly increased (2.9-fold) in the BALF of asthma subjects compared to controls.
• Asthma-associated M2 macrophages exhibited elevated production of IL-6, IL-10, and IL-12p40.
• Specific M2 macrophage subsets expressing histamine receptor 1 and E-cadherin correlated with increased airflow obstruction.
• M2 macrophages demonstrated the capacity to modulate dendritic and CD4+ T cell activation.

Conclusions:

• M2 macrophages possess a distinct phenotype and effector function that is altered in asthma.
• Increased numbers and altered functions of M2 macrophages in asthma suggest their significant contribution to the disease.
• M2 macrophages may influence asthma progression through interactions with immune and structural cells, and inflammatory mediators.