Accessory cells in normal human and rodent lymph nodes: morphology, phenotype, and functional implications

Area of Science:

• Immunology
• Cell Biology
• Histology

Background:

• Accessory cells are crucial for initiating specific host defense mechanisms within lymphoid tissues.
• Antigen presentation by accessory cells is a fundamental step in activating lymphocytes.
• The term 'dendritic cells' has largely replaced traditional terms like 'reticulum cells' due to their morphology and function.

Purpose of the Study:

• To review professional accessory cells in human and rodent lymph nodes.
• To delineate the characteristics and functions of different types of dendritic accessory cells.
• To differentiate accessory cells involved in cellular immunity (T accessory cells) versus humoral immunity (B accessory cells).

Main Methods:

• Review of existing literature on lymph node accessory cells.
• Characterization based on morphology, antigen presentation capability, and cell surface markers.
• Immunophenotypic and functional analysis of T and B accessory cells.

Main Results:

• Professional accessory cells exhibit dendritic morphology and express key immune receptors and molecules.
• Two main types of dendritic accessory cells exist: T accessory cells (e.g., lymphoid dendritic cells, veiled cells, interdigitating dendritic cells) and B accessory cells (follicular dendritic cells).
• T accessory cells, of myeloid origin, present processed antigens to initiate T-cell responses, secreting IL-1 and IL-6.
• Follicular dendritic cells are involved in secondary B-cell responses and form the structure of lymphoid follicles.

Conclusions:

• Accessory cells, particularly dendritic cells, are essential for orchestrating adaptive immune responses.
• Distinct subsets of dendritic accessory cells are specialized for either T-cell or B-cell mediated immunity.
• Understanding these cells provides insight into the initiation and regulation of immune reactions.