Which of the following are not antigen-presenting cells (APCs)?
(a) lymphocytes
(b) dendritic cells
(c) macrophages
(d) neutrophils
(e) monocytes
The correct answer and explanation is:
The correct answer is (a) lymphocytes and (d) neutrophils.
Antigen-presenting cells (APCs) are crucial for initiating an immune response by processing and presenting antigens to T-cells. These cells are responsible for capturing, processing, and presenting fragments of foreign antigens to T-cells, which is key to activating the adaptive immune system.
Here’s why lymphocytes and neutrophils are not considered APCs:
- Lymphocytes (option a) are not traditionally APCs. Lymphocytes, including T-cells and B-cells, are central to the adaptive immune system, but they do not primarily function as antigen-presenting cells. Instead, they interact with APCs to mount an immune response. For instance, B-cells can act as APCs, but their main role is antibody production rather than antigen presentation.
- Neutrophils (option d) are not considered effective APCs. While neutrophils are a type of white blood cell involved in the innate immune response, they are more specialized in phagocytosis and killing pathogens. They can present antigens, but their role is not as central to the adaptive immune response as other APCs like dendritic cells or macrophages.
On the other hand, the following cells are antigen-presenting cells:
- Dendritic cells (option b) are the most potent APCs. They are key in activating naïve T-cells by presenting antigens. They are found in tissues that are in contact with the external environment, such as the skin and mucosal membranes.
- Macrophages (option c) are large phagocytic cells that not only engulf pathogens but also present the processed antigens to T-cells, playing an important role in both the innate and adaptive immune systems.
- Monocytes (option e) are precursors to macrophages and dendritic cells. Upon entering tissues, they differentiate into macrophages or dendritic cells and can present antigens to T-cells.
In summary, lymphocytes and neutrophils are not classified as antigen-presenting cells, while dendritic cells, macrophages, and monocytes play key roles in antigen presentation.