Ly-49 Receptors or killer cell lectin-like receptor subfamily A (KLRA), member 1, are a class of natural killer cell

Natural killer cell

Natural killer cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses...

 receptor. Ly-49 proteins are a diverse set of C-type lectins that are expressed on NK cells in some mammals, including rodents but not humans. Their primary function is to bind host MHC class I

MHC class I

MHC class I molecules are one of two primary classes of major histocompatibility complex molecules and are found on every nucleated cell of the body...

 as a mechanism of self/health recognition. Upon binding ligands, most Ly-49 receptors will deliver an inhibitory signal, preventing killing of the target cell. In the case of cancer or virally infected cells, MHC-I will often be downregulated in order to limit cytotoxic T cell

Cytotoxic T cell

A cytotoxic T cell belongs to a sub-group of T lymphocytes that are capable of inducing the death of infected somatic or tumor cells; they kill cells that are infected with viruses , or are otherwise damaged or...

mediated killing of the cell, whereby NK cells will lack Ly-49 inhibitory signal and be able to kill infected or cancerous target cells.