immunology lecture 2

Primary and Secondary Lymphoid Organs

• Primary lymphoid organs are crucial for lymphocyte maturation; include bone marrow (B cells) and thymus (T cells).
• Secondary lymphoid organs, such as lymph nodes, spleen, and MALT, are where immune responses are activated.

Tertiary Lymphoid Organs

• Tertiary lymphoid organs develop in areas of chronic inflammation or infection, facilitating localized immune responses.

Types of Bone Marrow

• Yellow bone marrow is fatty tissue that stores fat and can transform into red marrow when there is an increased need for blood cell production.
• Red bone marrow is active in hematopoiesis, primarily located in flat bones and the ends of long bones.

Bone Marrow Structure

• Medullary cavity is the central area within long bones containing bone marrow, essential for blood cell creation.
• Endosteal niche is a specialized microenvironment near the bone surface that supports hematopoietic stem cells.
• Bone marrow vascular niche is where stromal cells and blood vessels interact with hematopoietic cells, regulating blood cell production.

Thymus Structure and Function

• The thymus is encased in a connective tissue capsule that offers support and protection.
• Subcapsular space beneath the thymic capsule houses developing thymocytes.
• Cortex of the thymus is where thymocytes undergo positive selection, while the medulla is where they face negative selection and mature T cells enter circulation.
• Thymic involution refers to the age-related decline in thymus size and function, reducing new T cell production.

Mucosa-Associated Lymphoid Tissue (MALT)

• MALT includes lymphoid tissues at mucosal surfaces like GALT, BALT, and NALT, essential for protecting mucosal areas and initiating immune responses.

Spleen Structure and Function

• Red pulp filters blood, removing damaged red blood cells and pathogens.
• White pulp contains lymphocytes that are integral to immune responses and antibody production.
• Periarteriolar lymphoid sheath (PALS) surrounds central arterioles in white pulp, containing T lymphocytes that aid immune responses.

Lymphoid Follicles and Germinal Centers

• Follicles in secondary lymphoid organs are clusters of B cells vital for activation and proliferation.
• Germinal centers are specialized environments in lymphoid follicles where B cells proliferate and differentiate.
• B cell corona forms the outer layer of a germinal center, primarily composed of B cells supporting the internal structure.

Marginal Zone and Perifollicular Zone

• The marginal zone at the interface of red and white pulp in the spleen has specialized macrophages and B cells.
• Perifollicular zone surrounds lymphoid follicles containing T cells, supporting coordinated immune responses.

Peyer’s Patches

• Peyer’s patches are clusters of lymphoid tissue in the ileum that monitor intestinal bacteria and play a role in initiating immune responses.

Lymph Flow Through Lymph Nodes

• Lymph fluid enters lymph nodes via afferent lymphatic vessels into the sub-capsular space (marginal sinus).
• The fluid moves through cortical (trabecular) sinuses and drains into the medullary sinus.
• Lymph exits the medullary sinus via efferent lymphatic vessels.
• The lymph is transported through lymphatic vessels to other lymph nodes before re-entering the bloodstream.