Which cells are known for engulfing foreign substances and aiding T cell activation?

The correct choice highlights the role of macrophages in the immune system. Macrophages are a type of phagocytic cell that play a crucial role in both innate and adaptive immunity. They have the ability to engulf and digest foreign substances, including pathogens, dead cells, and debris. This process is known as phagocytosis.

Additionally, macrophages contribute to T cell activation by presenting antigens. Once they engulf a pathogen, they process and present pieces of the antigen on their surface using molecules called Major Histocompatibility Complex (MHC) proteins. This antigen presentation is vital for the activation of T cells, which are essential for orchestrating the adaptive immune response, including the targeting of specific pathogens.

While other immune cells, such as neutrophils and dendritic cells, also participate in immune responses, their primary functions differ slightly. Neutrophils are primarily involved in the early response to infection and are less effective at antigen presentation compared to macrophages. Dendritic cells are indeed critical for T cell activation, but macrophages also have important roles in phagocytosis and further immune interactions. B cells primarily focus on antibody production and do not engage in phagocytosis in the same direct manner as macrophages.