Fig. 1.

Schematic illustration of the lymphatic vessel network and the lymph node architecture with specific lymphocytes. A) Sampling of the contents of the lymphatic fluid within the lymph nodes is a crucial component in initiating immune response. B) The lymph node is mainly divided into three areas: cortex, paracortex, and medulla, and various immune cells reside in distinct microzones to orchestrate the adaptive immune system. C) Pathogens transported in the lymph are deposited via afferent vessels into the subcapsular sinus [21]. Free antigen may be phagocytosed by subcapsular sinus macrophages or drain into the cortex, containing the D) germinal center (in ‘B-cell zone’) and E) an inner paracortex (or ‘T-cell zone’). The dendritic cells also enter the cortex in a chemokine/cytokine-mediated manner. B cells and T cells can be activated by antigen-presenting cells (e.g., the migrating or resident dendritic cells that scavenge free antigen) and clonally expand and differentiate in the germinal center (within the B-cell zone) and T-cell zone, respectively. Effector T cells, and antibody-secreting plasma cells are produced that enter the medulla and exit the LN to defend against foreign pathogens.