Adaptive Immunity vs Innate Immunity

Lymphatic System

• The lymphatic system consists of lymph, lymphatic vessels, structures, and organs containing lymphatic tissue, and red bone marrow.
• The lymphatic system's functions include draining excess interstitial fluid, transporting dietary lipids, and carrying out immune responses.
• Lymphatic vessels begin as lymphatic capillaries, which are closed at one end. They unite to form larger vessels, resembling veins in structure but with thinner walls and more valves.
• Lymphatic vessels pass through lymph nodes and encapsulated organs with masses of B and T cells.
• Lymphatic capillaries are slightly larger in diameter than blood capillaries and have a unique one-way structure. Anchoring filaments pull openings wider when interstitial fluid accumulates.

Immunity or Resistance

• Immunity or resistance involves the ability to ward off damage or disease, and there are two types of immunity: innate and adaptive.
• Innate, or nonspecific immunity, is present at birth and has no specific recognition of invaders. It includes a first and second line of defense.
• Adaptive, or specific immunity, involves specific recognition of invaders with a memory component.

Lymphoid Cells

• Lymphocytes are the main cells involved in the immune response, with two main types: T cells and B cells.
• T cells manage the immune response and attack/destroy foreign cells.
• B cells produce plasma cells, which secrete antibodies that immobilize antigens.
• Other lymphoid cells include macrophages (phagocytize foreign substances and help activate T cells), dendritic cells (similar to macrophages, gathering and transporting antigens to lymph nodes), and reticular cells (fibroblast-like cells supporting other cell types in lymphoid organs).

Lymphatic Tissues and Organs

• Lymphatic tissues and organs are grouped into two categories based on function: primary and secondary.
• Primary lymphatic organs (red bone marrow and thymus) are sites where stem cells divide and become immunocompetent (able to produce a normal immune response).
• Secondary lymphatic organs (lymph nodes, spleen, lymphatic nodules) are sites where most immune responses occur.

Lymphoid Organs

• Lymphoid organs include tonsils (in the pharynx), thymus (in the thorax), spleen (curves around the left side of the stomach), Peyer's patches (in the intestine), and the appendix.

Thymus

• The thymus contains thymic lobes with an outer cortex and inner medulla.
• The cortex has densely packed lymphocytes and scattered macrophages.
• The medulla has fewer lymphocytes and thymic (Hassall's) corpuscles.
• The thymus differs from other lymphoid organs by its function strictly in T lymphocyte maturation and lack of direct antigen-fighting.
• The thymus stroma consists of star-shaped epithelial cells (not reticular fibers).
• Thymocytes secrete hormones to stimulate lymphocytes for immunocompetence.

Lymph Nodes

• Lymph nodes are located along lymphatic vessels, scattered throughout the body, and have a fibrous capsule, trabeculae, and reticular fibers and fibroblasts as stroma.
• The parenchyma, the functional part, includes an outer cortex (aggregates of B cells forming lymphatic nodules—a site of plasma cell and memory B cell formation), an inner cortex (mainly T cells and dendritic cells), and a medulla (containing B cells, antibody-producing plasma cells from the cortex, and macrophages). Lymph flows through nodes in one direction.
• Lymph nodes are filtering stations for foreign substances, which are trapped and destroyed by macrophages or through the immune response of lymphocytes. There are two basic functions filtration and immune system activation.
• Lymph nodes are bean-shaped and surrounded by a fibrous capsule. Trabeculae extend inward, dividing the node into compartments. Nodes have a cortex and medulla. The cortex contains follicles with germinal centers (where B cells divide), dendritic cells, and superficial T cells. The medulla has medullary cords (B cells and plasma cells) and medullary sinuses.

Spleen

• The spleen is the largest single mass of lymphatic tissue in the body. Its stroma is composed of a capsule, trabeculae, reticular fibers, and fibroblasts. The parenchyma includes the white pulp (lymphatic tissue, including lymphocytes and macrophages), where B and T cells carry out immune functions, and the red pulp (blood-filled venous sinuses and splenic cords).
• The spleen removes ruptured, worn out, or defective blood cells. It stores up to one-third of the body's platelet supply and produces blood cells during fetal life. Its functions include lymphocyte proliferation, immune surveillance and response, blood cleansing, and storage.

Lymphatic Nodules

• Lymphatic nodules lack a capsule, are scattered throughout the lamina propria of mucous membranes, and include mucosa-associated lymphatic tissue (MALT) in the respiratory tract.
• Some lymphatic nodules are larger (tonsils, Peyer's patches, appendix).

Antigen Processing

• B cells can recognize and bind to antigens in lymph, interstitial fluid, or blood plasma.
• T cells only recognize fragments of antigens that are processed and presented in a certain way.
• Antigen-presenting cells (APCs) process antigens, and then present them to T cells.
• Endogenous and exogenous antigens are processed differently.

Cell-Mediated Immunity

• Cell-mediated immunity (CMI) involves cytotoxic T cells, which directly attack invading antigens, particularly effective against intracellular pathogens (viruses, bacteria, fungi), some cancer cells, and foreign tissue transplants.
• CMI involves cells attacking cells.
• Helper T cells aid in both cell-mediated and antibody-mediated immunity.

Antibody-Mediated Immunity

• Antibody-mediated immunity (AMI) involves B cells transforming into plasma cells producing antibodies (Abs) or immunoglobulins.
• Antibodies work against extracellular pathogens in fluids outside cells.
• Helper T cells aid in AMI.

Immunological Memory

• Thousands of memory cells exist after the initial encounter with antigen.
• Next time the antigen appears, memory cells can proliferate and differentiate within hours.
• Antibody titer is a measure of immunological memory (amount of Abs in the serum).
• Secondary response is faster and stronger than the primary response.

Self-Recognition and Self-Tolerance

• T cells must be able to recognize their own MHC molecules and lack reactivity to peptide fragments from their own proteins (self-tolerance).
• Failure to meet self-tolerance rules can lead to autoimmune diseases.
• T cells in the thymus develop self-recognition via positive selection and eliminate T cells that don't recognize self-MHC.
• Negative selection eliminates self-reacting T cells.

This quiz explores key concepts of adaptive immunity, comparing it with innate immunity. Test your understanding of the roles of various immune cells, including B cells, T cells, and macrophages, as well as the functions of lymphatic organs and responses during an immune reaction.