Question

Best antigen presenting cell is

• A. Mast cell
• B. B cell
• C. Neutrophils
• D. Dendritic cells

Hint:

• Professional Antigen-Presenting Cells (APCs): Dendritic cells, Macrophages, B cells.
• They express MHC class II molecules (for presenting to CD4+ T helper cells) and MHC class I molecules (on all nucleated cells, for presenting to CD8+ cytotoxic T cells).
• Dendritic cells are particularly specialized and efficient at capturing antigens in peripheral tissues and migrating to lymphoid organs to activate naive T cells.

Answer 1

The Correct Option is D

Antigen-Presenting Cells (APCs) are specialized cells that capture, process, and present antigens (fragments of pathogens or foreign substances) on their cell surface in conjunction with Major Histocompatibility Complex (MHC) molecules for recognition by T lymphocytes (T cells). This is crucial for initiating adaptive immune responses. There are several types of APCs:

• Professional APCs: These are highly efficient at antigen presentation and T cell activation. They include:
  • Dendritic Cells (DCs): Considered the most potent and effective professional APCs, especially for activating naive T cells and initiating primary immune responses. They are found in tissues and migrate to lymph nodes upon antigen capture. (Option d)
  • Macrophages: Phagocytic cells that can present antigens to T cells, particularly important in ongoing immune responses and for activating effector T cells.
  • B cells (B lymphocytes): Can internalize specific antigens via their B cell receptors (antibodies), process them, and present them to helper T cells. This T cell help is often required for B cell activation and antibody production. (Option b)
• Non-professional (Atypical) APCs: Some other cell types (e.g., fibroblasts, thymic epithelial cells) can express MHC class II molecules under certain conditions (e.g., inflammation) and present antigens, but this is not their primary role.

Among the professional APCs, dendritic cells are generally considered the "best" or most potent at initiating T cell responses, especially for naive T cells, due to their high expression of MHC molecules, co-stimulatory molecules, and their migratory capacity. Let's analyze the options: (a) Mast cell: Primarily involved in allergic reactions and defense against parasites by releasing histamine and other mediators. Not considered a primary APC for T cell activation. (b) B cell: A professional APC, but dendritic cells are generally more potent for initiating T cell responses. (c) Neutrophils: Phagocytic cells crucial in innate immunity and acute inflammation. They are not typically considered professional APCs for T cell activation in the same way as DCs, macrophages, or B cells, though they can present some antigens. (d) Dendritic cells: The most potent professional APCs. Therefore, dendritic cells are considered the best antigen-presenting cells for initiating adaptive immunity. \[ \boxed{\text{Dendritic cells}} \]