Notes on the Lymphatic (Immune) System

The Lymphatic (Immune) System

Innate (Non-Specific) Defenses

• Six Mechanisms of Innate Defense:

  • Species Resistance:

  • Certain species are naturally resistant to diseases affecting other species.

  • Environmental factors of the body can prevent pathogen survival.

  • Mechanical Barriers:

  • Considered the "First line of Defense."

  • Includes skin and mucus membranes which keep pathogens out.

  • Bodily fluids like sweat and mucus help rinse away pathogens.

  • Chemical Barriers:

  • Body fluids contain enzymes that digest pathogens.

  • Examples: Stomach acid and tear enzymes.

  • Interferon:

  • Peptides responding to viruses and tumor cells, blocking virus replication and stimulating phagocytosis.

  • Fever:

  • Elevated body temperature restricts iron availability from the liver and spleen, hindering bacterial and fungal survival.

  • Increases the activity of phagocytic cells.

  • Inflammation:

  • Provides a localized response to tissue damage and pathogen presence.

  • Phagocytosis:

  • Specialized cells that engulf and digest pathogens.

Adaptive Immunity

• Specific Defenses:

  • Provides resistance to specific pathogens or toxins (specific types of immunity).

  • Immunity:

  • Developed through exposure, allowing lymphocytes and macrophages to "remember" pathogens for future protection.

  • Antigens:

  • Recognition molecules, typically proteins or sugars, utilized by the immune system to distinguish self from non-self substances.

Lymphocyte Origins

• Red Bone Marrow:

  • Releases stem cells for lymphopoiesis (the formation of lymphocytes).

  • Half of these stem cells migrate to the thymus to become T Cells.

  • The other half remain in bone marrow to mature into B Cells.

T Cell Activation

• Circulation:

  • T cells circulate in the blood looking for antigens ("trouble").

• Activation Process:

  • Antigen Presenting Cells (APC), such as macrophages and B cells, present foreign antigens to T cells to activate them.

• Macrophage Activity:

  • Macrophages consume pathogens and present antigens combined with Major Histocompatibility Complex (MHC) molecules to T cells to activate an immune response.

Cellular Immune Response

• Types of T Cells:

  • T-Helper (CD4):

  • Activates B cells.

  • T-Cytotoxic (CD8):

  • Recognizes foreign antigens on infected or cancerous cells and kills them.

  • T-Memory Cells:

  • Persist after an infection, allowing faster responses if the same pathogen reappears.

B Cell Functionality

• Development:

  • B cells mature in bone marrow, with some circulating while others reside in immune organs.

• Humoral Immune Response:

  • B cells combat pathogens by releasing antibodies through plasma cells.

  • Antibodies, also known as Immunoglobulins (Ig), play a crucial role in identifying and neutralizing pathogens.

Types of Antibodies

• IgG:

  • Predominant in plasma and tissues, crosses the placenta, and combats bacteria, viruses, and toxins.

• IgM:

  • Present in blood, examples include Anti-A and Anti-B, involved in the response against bacterial antigens.

• IgA:

  • Found in mucosal areas (e.g., breast milk, tears, gastric juice); acts as a first line of defense in secretions.

• IgD:

  • Located on B cell surfaces, particularly in children, important for B cell activation.

• IgE:

  • Associated with allergic reactions, binds to mast cells to trigger responses upon allergen contact.

Mechanisms of Action of Antibodies

• Direct Attack:

  • Antibodies bind to antigens to neutralize them or cause clumping for easier phagocytosis.

• Complement Activation:

  • Binding of IgG and IgM activates complement proteins, which can opsonize pathogens, attract phagocytic cells, and cause cell membrane lysis.

Immune Response Dynamics

• Primary Immune Response:

  • First encounter with a pathogen, slow antibody production lasts weeks.

• Secondary Immune Response:

  • Re-exposure leads to quicker antibody production due to memory cells, providing faster protection.

Types of Immunity

• Natural vs. Artificial:

  • Natural immunity occurs through everyday exposure, whereas artificial immunity is obtained through intentional exposure like vaccines.

• Active vs. Passive:

  • Active immunity is generated when the body produces antibodies, providing long-lasting protection.

  • Passive immunity involves receiving antibodies from another source, offering temporary protection.

• Examples:

  • Natural, active immunity could arise from a pneumonia infection; natural, passive from breastfeeding; artificial, active from vaccinations; artificial, passive from antivenoms or antitoxins.