Which of the following is not an antigen-presenting cell (APC)?
A) macrophage
B) dendritic cell
C) T cell
D) B cell
The correct answer and explanation is:
The correct answer is C) T cell.
Antigen-presenting cells (APCs) are specialized cells that process and present antigens to T cells, which helps trigger an adaptive immune response. The main APCs in the immune system include macrophages, dendritic cells, and B cells. T cells, however, are not considered antigen-presenting cells.
- Macrophages are large white blood cells that engulf pathogens, dead cells, and other debris in the body. After ingestion, they break down these particles and present antigens on their surface using molecules called major histocompatibility complex (MHC) class II molecules. This allows T cells, specifically helper T cells, to recognize and respond to the antigens.
- Dendritic cells are perhaps the most potent APCs and play a critical role in initiating immune responses. They capture antigens from the environment, process them, and then migrate to lymph nodes where they present these antigens to T cells. Dendritic cells can activate both helper T cells and cytotoxic T cells, making them essential in both the innate and adaptive immune responses.
- B cells are part of the adaptive immune system and can also act as APCs. They internalize antigens, process them, and present them on their surface using MHC class II molecules. In addition to presenting antigens, B cells can produce antibodies that bind to the antigens and mark them for destruction.
- T cells, unlike the other cells mentioned, do not primarily function as antigen-presenting cells. T cells recognize antigens presented by APCs and participate in immune responses. However, T cells themselves do not present antigens to other T cells. They play a crucial role in cell-mediated immunity, but they are not APCs.
In summary, T cells are involved in immune responses but do not act as antigen-presenting cells, which distinguishes them from macrophages, dendritic cells, and B cells.