**Question:** Cellular immunity is induced by-

A. Antigen-presenting cells (APCs)
B. Monoclonal antibodies
C. Natural killer cells (NK cells)
D. Immunosuppressive drugs

**Core Concept:**
Cellular immunity is a part of adaptive immunity that involves the activation, proliferation, and differentiation of immune cells to recognize and eliminate pathogens, cancer cells, and abnormal cells. The primary components of cellular immunity include T cells, B cells, and natural killer (NK) cells. Antigen-presenting cells (APCs), such as dendritic cells, macrophages, and B cells, play a crucial role in initiating the immune response by presenting antigens to T cells.

**Why the Correct Answer is Right:**
Cellular immunity is primarily induced by antigen-presenting cells (APCs) like dendritic cells, macrophages, and B cells. These cells capture and process antigens, which are then presented to T cells via major histocompatibility complex (MHC) molecules. This interaction triggers the activation and proliferation of T cells, which in turn target and eliminate infected or abnormal cells.

**Why Each Wrong Option is Incorrect:**

A. Monoclonal antibodies are artificial molecules that can neutralize specific antigens or receptors, not induce cellular immunity. They are used to target and eliminate pathogens or cancer cells but not the mechanism of cellular immunity induction.

B. Monoclonal antibodies are not involved in the induction of cellular immunity, as they target specific antigens or receptors, not initiate the immune response itself.

C. Natural killer (NK) cells are cytotoxic lymphocytes that kill virus-infected cells, cancer cells, and cells with missing or abnormal MHC molecules. While NK cells are part of the immune system, they are not responsible for inducing cellular immunity, which depends on antigen-presenting cells and T cells.

D. Immunosuppressive drugs, such as corticosteroids and calcineurin inhibitors, primarily dampen the immune response to prevent organ transplant rejection and manage autoimmune disorders. They do not induce cellular immunity but rather suppress it.

**Clinical Pearls:**

1. Cellular immunity plays a vital role in combating infections, eliminating cancer cells, and recognizing abnormal cells.
2. Antigen-presenting cells, specifically dendritic cells, macrophages, and B cells, are crucial in initiating the immune response via presenting antigens to T cells.
3. Monoclonal antibodies target specific antigens or receptors, not participate in cellular immunity induction.
4. Natural killer (NK) cells are cytotoxic lymphocytes involved in killing virus-infected cells, cancer cells, and cells with missing or abnormal major histocompatibility complex (MHC) molecules.
5. Immunosuppressive drugs, such as corticosteroids and calcineurin inhibitors, dampen the immune response in specific clinical scenarios but do not induce cellular immunity.