Lymphatic System and Immune Response Mechanisms

Lymphatic System Pathway

The flow of lymph follows this sequence: peripheral tissues → lymphatic capillaries → afferent vessels → lymph nodes → efferent vessels → lymphatic ducts → venous system (subclavian veins).

Key Lymphatic Organs

• Lymph Nodes: Act as a filter and early warning system.
• Thymus: Site for actively dividing and maturing T cells; maintains the blood-thymus barrier, separating developing T cells from general circulation; produces hormones.
• Spleen: Removes abnormal red blood cells (RBCs) via phagocytosis, stores iron from recycled RBCs, and initiates B and T cell immune responses to antigens.

MHC Proteins and T Cell Activation

• Class I MHC Protein: Synthesized by all cells in the body. They pick up small peptides from the cytoplasm and carry them to the cell surface. If the cell is healthy, it is ignored; if abnormal, T cells are activated.
• Class II MHC Protein: Found only in the plasma membrane of Antigen-Presenting Cells (APCs). APCs use these to activate T cell defenses.
• CD8 Markers: Found in cytotoxic and regulatory T cells. The plasma membrane of an infected cell triggers an immune response when CD8 recognizes antigens bound to Class I MHC.
• CD4 Markers: Found in helper T cells; these trigger responses to extracellular pathogens.

Antigen-Antibody Complex Functions

Antibodies eliminate pathogens through the following mechanisms:

• Neutralization: Antibody binds to sites, making the virus incapable of attaching itself.
• Precipitation: Formation of insoluble immune complexes.
• Agglutination: Formation of large complexes.
• Activation of Complement System: Antibody binding to an antigen changes the antibody shape, exposing areas that bind complement proteins.
• Attraction to Phagocytes: Antigens covered with antibodies attract eosinophils and macrophages, which phagocytize the pathogen and destroy the foreign plasma membrane.
• Opsonization: Coating with antibodies and complement proteins increases the effectiveness of phagocytosis.
• Stimulation of Inflammation: Stimulates basophils.
• Prevention of Adhesion: Antibodies cover pathogens, making it difficult for them to attach to and penetrate body surfaces.

Immune Response Timing

The relative response times are as follows:

• Shortest duration: NK cells
• 2nd shortest: Cytotoxic T cells
• 3rd shortest: Neutrophils (highest peak)
• 4th shortest: Macrophages
• Longest duration: Plasma cells
• Late onset/Late end: Antibody titer

Anaphylaxis

Anaphylaxis: A reaction caused by a circulating allergen resulting in widespread inflammation.
Anaphylactic Shock: Extensive peripheral vasodilation occurs, causing a drop in blood pressure that leads to circulatory collapse.