Which statement is true regarding the major histocompatibility complex (MHC) proteins?

The major histocompatibility complex (MHC) proteins play a critical role in the immune system by facilitating the recognition of self versus non-self. MHC molecules are essential for the presentation of peptide fragments derived from proteins that are expressed on the surface of cells. There are two primary classes of MHC molecules: class I and class II. Class I MHC proteins are found on nearly all nucleated cells and are responsible for presenting antigens to CD8+ cytotoxic T cells, which can then recognize and eliminate infected or abnormal cells. Class II MHC proteins are primarily expressed on antigen-presenting cells, such as dendritic cells, macrophages, and B cells, and they present antigens to CD4+ helper T cells.

This function is vital for distinguishing between the body's own cells and foreign cells or pathogens, such as viruses or bacteria. The ability of MHC proteins to present these antigens is crucial for initiating appropriate immune responses. The recognition of self versus non-self is fundamental for the immune system's ability to protect the body without attacking its own tissues.

In contrast, the other statements do not accurately represent the role or distribution of MHC proteins. MHC proteins are not restricted to red blood cells, nor are they limited