Only antigen-presenting cells such as dendritic cells, macrophages, and B-lymphocytes produce MHC-II molecules. Peptide epitopes bound to MHC-II molecules are recognized by TCRs and CD4 molecules on the surfaces of naive T4-lymphocytes and on effector T4-lymphocytes.

Why don't all nucleated cells in our body produce MHC-II molecules as well as MHC-I molecules?

Why is it important for dendritic cells to produce both MHC-I and MHC-II molecules?