Consider two receptors, one inhibitory and one activating, on the surface of natural killer (NK) cells: KIR receptors that interact with certain class I MHC proteins, and special Fc receptors that recognize the tail region of IgG antibodies. When NK cells are incubated with an immortalized B cell line derived by infection of human B cells with Epstein-Barr Virus, the B cells are killed by NK cells. Normal B cells, in contrast, are not efficiently killed by NK cells. In each of the following scenarios, indicate whether the described changes are expected to enhance (E) or suppress (S) the cytotoxicity (killing activity) of the NK cells in this system. Your answer would be a four-letter string composed of letters E and S only, e.g. SEEE.
( ) The cell line is transformed with human class I MHC genes, and the genes are expressed.
( ) An anti-CD23 IgG antibody is added to the cells. (CD23 is a known marker on the surface of the immortalized B cells.)
( ) The cells are treated with stibogluconate, an inhibitor of KIR receptor signaling.
( ) Type I interferons are added to the cells.

Question

Consider two receptors, one inhibitory and one activating, on the surface of natural killer (NK) cells: KIR receptors that interact with certain class I MHC proteins, and special Fc receptors that recognize the tail region of IgG antibodies. When NK cells are incubated with an immortalized B cell line derived by infection of human B cells with Epstein-Barr Virus, the B cells are killed by NK cells. Normal B cells, in contrast, are not efficiently killed by NK cells. In each of the following scenarios, indicate whether the described changes are expected to enhance (E) or suppress (S) the cytotoxicity (killing activity) of the NK cells in this system. Your answer would be a four-letter string composed of letters E and S only, e.g. SEEE.
( )	The cell line is transformed with human class I MHC genes, and the genes are expressed.
( )	An anti-CD23 IgG antibody is added to the cells. (CD23 is a known marker on the surface of the immortalized B cells.)
( )	The cells are treated with stibogluconate, an inhibitor of KIR receptor signaling.
( )	Type I interferons are added to the cells.

Quizplus · Accepted Answer

The KIR receptors that bind to class I MHC proteins initiate inhibitory signals upon binding and therefore suppress NK cytotoxicity. Viral infection tends to decrease the expression of class I MHC proteins by host cells, which partly explains why the virus-infected B cells are susceptible to NK cytotoxicity, whereas normal B cells are not. Inhibition of the KIR receptor inhibitory signal by stibogluconate, therefore, enhances NK cell killing. Additionally, the Fc receptors that bind to the immunoglobulin G (IgG) Fc regions enhance NK cell killing of target cells coated with IgG antibodies. Finally, type I interferons enhance NK cell killing activity in general.

Consider Two Receptors, One Inhibitory and One Activating, on the Surface