Veterinary Immunology and Serology

LYMPH NODES

• Lymph nodes are bean shaped structure found in large number along the course of lymphatic vessels and connected to each other by lymphatic to trap antigen carried by lymph.
• Lymph nodes are covered with fibrous capsule and each one has an outer cortex, inner medulla and para cortical zone in between them.
• Lymph node consists of a reticular network filled with lymphocytes, macrophages, dendritic cells through which lymphatic sinuses penetrate.
• Cortex
• Beneath the sub capsular sinus, the outer cortex is area of B. lymphocytes which are present as aggregate in the form of primary folicles (containing mainly naive mature B-cells) and secondary folicles (germinal centre).
• Naive B cells are attracted to the follicle in response to chemokines produced in follicles and expressed chemokine receptor.
• Some follicles contain central germinal centre, which develop on antigenic stimulation, and they are called secondary follicles.
• Germinal centres are sites of B cell maturation (somatic maturation), immunoglobulin class switching and memory cell formation. Primary follicle mostly contains mature, naïve B-lymphocytes.
• The follicular dendritic cells (FDCs) present in the germinal center, trap antigen and present to B cells.
• A few T cells are found in the cortex, mainly between follicles. About 70% of these T cells are CD4+ (helper T cells) and relatively less CD8+cells.
• Para cortex
• The paracortical area of the lymph node is the site for homing of T-cells and interdigitating dendritic cells, where DC capture antigen, process and present them to the T-cells.
• Medulla
  • Predominant cells are B cells, macrophages, reticular cells and plasma cells.
  • They are arranged in cellular cords between the lymphatic sinuses.
  • Activated T and B cells migrate towards one another.
• Activated T cells ultimately exit lymph node and enter the circulation where as activated B cells migrate into germinal centre or medulla and secrete antibodies.
• Other animals: In pigs, elephants, hippopotamuses, rhinoceroses and dolphins, lymph nodes consist of several aggregated nodules. Cortex is located toward the centre and medulla is at the periphery.