Thus, the observed change of proteasomal composition and activity in BAL supernatant of ARDS patients may be caused by replacement of standard 20S proteasome proteins by catalytic subunits β1i (LMP2), β2i (MECL-1), and β5i (LMP7) that are incorporated into a newly synthesized intermediate type and/or immunoproteasome. The gene discussed is PSMB9; the disease is acute respiratory distress syndrome.