Final answer:
Dendritic cells in lymphoid tissue function as antigen-presenting cells, capturing and processing antigens to present to T cells, thereby activating an immune response. They perform phagocytosis of pathogens and mobilize T cells and B cells in lymphoid structures like lymph nodes and Peyer's patches.
Step-by-step explanation:
Dendritic cells are essential components of the immune system, particularly in the lymphoid tissues where they serve as critical antigen-presenting cells (APCs). They are found in tissues that are in contact with the external environment, such as the skin, nose, lungs, stomach, and intestines. Their key role is to capture and process antigens, which are foreign substances, and present them on their surface to T cells within the lymphoid tissues, specifically in the lymph nodes. Upon encountering pathogens, dendritic cells perform phagocytosis to ingest and break down these pathogens. After digestion, the dendritic cells present parts of the pathogens, known as antigens, on their surface using MHC II molecules. This presentation is crucial for the activation of T cells, which then become informed about the presence of potential pathogens and initiate an adaptive immune response. Dendritic cells also travel to sites like the Peyer's patches in the intestines or MALT (mucosa-associated lymphoid tissue) where they continue to activate immune cells, leading to the production and secretion of antibodies such as IgA into the intestinal lumen and other mucosal surfaces.