[Lymphoid tissue during phylo- and ontogenesis]

Area of Science:

• Evolutionary biology
• Immunology
• Hematology

Context:

• Lymphoid tissues evolved from a unified hemolymphatic system.
• A persistent relationship exists between lymphoid and myeloid tissues throughout evolution and development.
• Perivascular lymphoid accumulations are observed in various organs.

Purpose:

• To describe the evolutionary and developmental relationship between lymphoid and myeloid tissues.
• To highlight the formation of organoid-perivascular lymphoid follicles in mammals.
• To detail the location of these lymphoid structures within the circulatory system.

Summary:

• During evolution, lymphoid tissue separated from the hemolymphatic system into distinct immune organs.
• Despite separation, close associations between lymphoid and myeloid tissues persist, seen as perivascular lymphoid accumulations.
• In mammals, this tissue differentiates into organized perivascular lymphoid follicles along blood and lymphatic vessels.

Impact:

• Provides insight into the evolutionary trajectory of the immune system.
• Clarifies the anatomical and developmental connections between different tissue types.
• Establishes the significance of perivascular lymphoid structures in mammalian immunity.