Which type of cells are the primary antigen-presenting cells?

The correct answer highlights that macrophages are the primary antigen-presenting cells, which is a fundamental concept in immunology. Macrophages play a crucial role in the immune system by engulfing pathogens and cellular debris through a process known as phagocytosis. After ingesting these antigens, macrophages process and present the antigenic components on their surface using molecules known as Major Histocompatibility Complex (MHC) class II proteins. This is essential for activating T-lymphocytes, particularly CD4+ T helper cells, which are vital for orchestrating the immune response.

While B-lymphocytes can also present antigens, their primary role is to produce antibodies in response to specific antigens. T-lymphocytes, on the other hand, are primarily involved in the cell-mediated immunity and do not typically present antigens. Neutrophils, while important for innate immunity and rapid response to infection, do not act as antigen-presenting cells. Therefore, the function of macrophages as the main antigen-presenting cells is critical for the adaptive immune response, facilitating the interaction between the innate and adaptive systems.