IMMUNOLOGY

Detailed explanation-1: -Antigenic peptide-loaded MHC class II molecules (peptide–MHC class II) are constitutively expressed on the surface of professional antigen-presenting cells (APCs), including dendritic cells, B cells, macrophages and thymic epithelial cells, and are presented to antigen-specific CD4+ T cells.

Detailed explanation-2: -In contrast to MHC class I molecules, MHC class II molecules have a more restricted distribution pattern, and they are predominantly expressed, under normal conditions, by professional antigen-presenting cells (APC), like B cells, macrophages and dendritic cells.

Detailed explanation-3: -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-4: -The main types of professional APCs are dendritic cells (DC), macrophages, and B cells. A professional APC takes up an antigen, processes it, and returns part of it to its surface, along with a class II major histocompatibility complex (MHC).