Can any cell present an antigen on a class II major histocompatibility complex (MHC) protein?

The correct answer is that not all cells can present an antigen on a class II major histocompatibility complex (MHC) protein. Class II MHC molecules are primarily expressed on specialized antigen-presenting cells (APCs), which include dendritic cells, macrophages, and B cells. These cells have the unique capability to process and present extracellular antigens to CD4+ T helper cells, which is crucial for initiating adaptive immune responses.

In contrast, most other cell types, such as somatic or non-immune cells, do not express class II MHC proteins and therefore cannot present antigens using this pathway. This selective expression is vital for immune regulation and for ensuring that T cells are activated appropriately in response to pathogens.