SBA — Single Best Answer · Review
Question 613
Immunology → General
Classification
Question
SSBAQuestion Header
Which phenotype and functional property best identifies a natural killer cell?
Question Stem
Select the single best answer.
Options
A
CD3 positive and dependent on prior antigen sensitisation
B
CD19 positive and responsible for antibody production
C
CD3 negative, CD16/CD56 positive, with spontaneous cytotoxic activity
D
CD4 positive and MHC class II restricted
E
CD8 positive and necessarily MHC class I restricted
Explanation
Natural killer cells are distinct from T and B lymphocytes. They are CD3 negative and CD16/CD56 positive, require no prior antigen sensitisation and can kill target cells spontaneously.
Option Validity
A) Natural killer cells are CD3 negative and do not require prior antigen sensitisation.
B) CD19 is a B-cell marker; B cells mediate humoral antibody responses.
D) CD4 positivity with MHC class II restriction characterises helper T cells.
E) CD8 positivity with MHC class I restriction characterises cytotoxic T-cell activity rather than the defining natural-killer-cell phenotype.
Further Reading
Saxena MRCOG-1 Basic Sciences — Immunology: Natural killer cells, printed page 211.