Scientists have discovered that macrophages (a type of immune cell) have a key role in activating MAIT cells, which are important for the body's defense against infections[1][2]. Macrophages from the lung and abdominal cavity showed the highest levels of MR1 protein and were most efficient at capturing and presenting bacterial antigens to MAIT cells[1][2]. The expression of MR1 in macrophages was regulated by the tissue environment and the organism's microflora[1]. When researchers removed MR1 from macrophages, dendritic cells and monocytes, the composition of the microbiota changed and the response of MAIT cells against bacterial infections was weakened[1][2]. Research has shown that interferon-gamma (IFNγ) produced by activated MAIT cells stimulates the expression of MR1, leading to greater activation of MAIT cells[3]. These findings suggest that macrophages are crucial for MR1 antigen presentation and MAIT cell immunity, which has implications for understanding the body's immune response to infections[1][2].