IMMUNOLOGY

Detailed explanation-1: -Class II major histocompatibility complex molecules (MHC class II) are highly expressed on the surface of epithelial cells (ECs) in both the lung and intestine, although the functional consequences of this expression are not fully understood.

Detailed explanation-2: -Although undetectable on resting T cells, MHC class II molecules are expressed to a high level on activated T cells. The role of class II molecules constitutively expressed on antigen-presenting cells (APC) is well documented with regard to antigen presentation to CD4+ T cells.