Virus infected cell is killed by –
**Core Concept**
The body has several mechanisms to eliminate infected cells, particularly those infected with viruses. One such mechanism is the activation of cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, which recognize and destroy infected cells through cell-mediated immunity.
**Why the Correct Answer is Right**
The correct answer involves the action of CTLs and NK cells, which recognize and kill infected cells through the release of cytotoxins and the activation of apoptosis. CTLs recognize viral antigens presented by major histocompatibility complex (MHC) class I molecules on the surface of infected cells. This recognition triggers the release of cytotoxins, such as perforin and granzymes, which create pores in the cell membrane and induce apoptosis in the infected cell. NK cells, on the other hand, recognize and kill infected cells through the activation of the Fas/Fas ligand pathway and the release of perforin and granzymes.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not involve the action of CTLs and NK cells, which are the primary mechanisms for eliminating infected cells through cell-mediated immunity.
**Option B:** This option is incorrect because it refers to the action of macrophages, which are primarily involved in the elimination of foreign particles and dead cells through phagocytosis.
**Option C:** This option is incorrect because it refers to the action of antibodies, which are primarily involved in the elimination of pathogens through the activation of complement and the opsonization of pathogens.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that cell-mediated immunity plays a crucial role in eliminating infected cells, particularly those infected with viruses. CTLs and NK cells are the primary mechanisms for eliminating infected cells through cell-mediated immunity.
**Correct Answer: A. CTLs and NK cells.**