Chapter 12, Problem 1Q

Summary Introduction

Introduction:

NK cells (natural killer cells) are also known as K cells or killer cells are white blood cells and play role in innate immune responses. NK cells protect host body by fighting against cancer and viral infections as these cells target tumor cells and cells infected by viruses. These cells express different kinds of cell surface receptors to target cells.

Answer to Problem 1Q

Correct answer:

The correct answer is option (a) 'receptors to recognize alterations to the human cell surface.'

Explanation of Solution

Explanation/justification for the correct answer:

NK cells are immune cells that express various activating and inhibitory receptors present on the cell surface. Virus-infected cells or tumor cells show altered cell surface proteins, which are absent in normal cells. Receptors on NK cells recognize those altered proteins and activate the pathway to produce cytokine and kill target cells.

Option (a) is given as 'receptors to recognize alterations to the human cell surface.' Hence, it is the correct option. Generally, immune cells require antibodies and major histocompatibility complex (MHC) molecules to recognize infected cells. However, receptors present on NK cells surface are able to recognize stressed cells in the absence of MHC and antibody molecules and make them unique. Recognition of target cells is followed by the release of cytokines and the death of those cells by apoptosis.

Option (b) is given as receptors to detect cellular stress. NK cells express receptors for antibodies, mainly for (immunoglobulin G or IgG) and play role in antibody-dependent cell mediated cytotoxicity.

Option (c) is given as receptors for the IgG Fc region. Thus, it is the correct option. NK cells also express TLRs (toll-like receptors) to sense and target bacterial and viral infected cells. These receptors recognize various bacterial and viral components, such as nucleic acid and lipopolysaccharide.

Option (d) is given as Toll-like receptors. Thus, it is the correct answer.

Option (e) is given as all of the above. Options (a), (b), (c), and (d) are correct. Hence, the correct answer is option (e).

Conclusion

Thus, the correct answer is option (e) as NK cells express receptors for altered cells, for stress cells, for IgG antibody, and toll-like receptors.