Here, we summarize the existing research on the expression of MHC II on non-professional APCs in different lung diseases and its influence on CD4+T differentiation types and disease outcomes, in order to further clarify the role of MHC II of different non-professional APCs in lung diseases, such as asthma, chronic obstructive pulmonary disease (COPD), etc. This evidence concerns the gene CD4 and chronic obstructive pulmonary disease.