Which of the following molecules on the surface of a cell does CD8 help to recognize? A) TLRs B) Selectins C) MHC II D) MHC I E) BCRs

D) MHC I

CD8 is a protein found on the surface of killer T cells (also known as cytotoxic T lymphocytes, or CTLs) and is part of the immune system. CD8 serves as a co-receptor that assists the T cell receptor (TCR) in recognizing antigens presented by the class I major histocompatibility complex (MHC I) molecules on the surface of cells. Every nucleated cell in the body presents MHC I molecules on its surface. These molecules display peptides (small protein fragments) from inside the cell, including peptides derived from viruses or other pathogens if the cell is infected. When CD8 and the TCR on a killer T cell recognize an antigen presented by MHC I on a diseased cell, it can lead the T cell to kill the diseased cell in an effort to control the infection or disease.

A) TLRs - Toll-like receptors (TLRs) are a type of pattern recognition receptor (PRR) that recognize pathogen-associated molecular patterns (PAMPs). They are not directly recognized by CD8.

B) Selectins - Selectins are a family of cell adhesion molecules that are not involved with antigen presentation. They play a role in the trafficking of leukocytes to sites of inflammation.

C) MHC II - Major Histocompatibility Complex class II (MHC II) molecules are found on the surface of certain immune cells like dendritic cells, macrophages, and B cells. They present antigens to helper T cells (CD4+ T cells), not to killer T cells.

E) BCRs - B cell receptors (BCRs) are found on the surface of B cells. They bind specific antigens, and this binding can lead to B cell activation and subsequent antibody production. They are not involved with T cell antigen recognition like MHC I.