The levels of left lung CD206 in the BLM + MHA, BLM + HHA, and BLM + MIX HA groups were statistically higher than that of the Normal group; among the groups, the CD206 level of the BLM + MIX HA group was significantly higher than that of the BLM group (Figure 5E), suggesting that medium-, high-, or mixed-molecular-weight HA could promote the differentiation and transformation of M2 macrophages to perform anti-inflammatory functions in the left lung of rats with severe ARDS. Here, MRC1 is linked to acute respiratory distress syndrome.