Are B cells capable of acting as antigen-presenting cells (APCs)?

• A. No, they are not
• B. Yes, but only in the spleen
• C. Yes, they can
• D. Only after activation by T cells

Answer: (C)

B cells are indeed capable of acting as antigen-presenting cells (APCs), and this ability plays a crucial role in the immune response. As APCs, B cells can process and present antigens to helper T cells. This interaction is essential for the activation of T cells, which in turn helps to stimulate B cells to produce antibodies against the specific antigens they present.

B cells express major histocompatibility complex (MHC) class II molecules on their surface, allowing them to present protein antigens to CD4+ T helper cells. This process occurs not just in the spleen but also in various other lymphoid tissues and sites of immune activation. Therefore, their ability to act as APCs is not restricted to the spleen or dependent solely on activation by T cells. In essence, the capacity of B cells to present antigens underscores their dual role in both humoral immunity (through antibody production) and cellular immunity (by facilitating T cell activation).