Animal Immune System: Innate and Adaptive Immunity

• The immune system is a complex network in animals that protects against pathogens like bacteria, viruses, and parasites.
• The animal immune system is divided into innate and adaptive immunity.

Innate Immunity

• The body's first line of defense responds quickly to pathogens.
• Physical barriers such as skin, mucous membranes, macrophages, and neutrophils are included.
• Inflammation is triggered when tissues are injured or infected, isolating and eliminating pathogens.
• This process involves increased blood flow, swelling, and the recruitment of immune cells to the affected area.

Adaptive Immunity

• This system takes longer to activate (days to weeks) to provide a targeted response to specific pathogens.
• Lymphocytes, specifically B cells and T cells, are involved.
• B cells produce antibodies that neutralize pathogens or mark them for destruction.
• T cells regulate the immune response and directly kill infected cells.
• Some B and T cells become memory cells after an infection, allowing for a quicker and stronger response if the same pathogen is encountered again in the future.
• The plant immune system is a complex network of defense mechanisms.
• It protects from pathogens, pests, and environmental factors.
• A key distinction is that it only has an innate immune system, unlike the animal immune system, which has an extra adaptive immune system.
• The plant immune system has two different recognition systems that initiate plant immunity.

Pattern-Triggered Immunity (PTI)

• Plant cell surface receptors (Pattern Recognition Receptors, or PRRs) detect Pathogen-Associated Molecular Patterns (PAMPs) to trigger immune responses.
• PTI provides initial protection and prepares the plant for stronger defenses.

Effector-Triggered Immunity (ETI)

• Resistance proteins, such as Nucleotide Binding Leucine-Rich Repeat (NB-LRR), detect effector molecules secreted by pathogens.
• This triggers a hypersensitive response.
• An oxidative burst produces Reactive Oxygen Species (ROS), leading to rapid cell death and pathogen isolation.
• ETI is typically stronger and faster than PTI.

Plants vs. Animals

• Plants lack an adaptive immune system and have no specialized mobile immune cells.
• Plants use rigid cell walls, cuticles, and secondary metabolites for protection.
• Localized cell death (hypersensitive response) is used to block pathogen spread.
• Animals have an adaptive immune system with specialized immune cells, like macrophages, neutrophils, and lymphocytes.
• Animals use skin, mucous membranes, and secretions like tears and saliva as barriers.
• Animals use inflammation, phagocytosis, and immune cell activation.

Similarities

• Both plants and animals recognize pathogens.
• Both systems trigger a response upon detection of a threat.
• Both plants and animals produce antimicrobial compounds to fight infections and rely on innate immunity as a first line of defense.

Contribution of Plant Immune Systems to Survival

• Prevention of infection: physical barriers and chemical defenses.
• Rapid response to threats: pattern recognition receptors and the Hypersensitive Response (HR)

Long-term Immunity

• Systemic Acquired Resistance (SAR) and resource allocation.

Contribution of Animal Immune Systems to Survival

• Protection against pathogens: Innate immunity and inflammatory response.
• Specific targeting of pathogens: Adaptive immunity and memory cells.
• Homeostasis and health maintenance: Cytokines and signaling molecules.
• Survival and reproduction.
• Both plant and animal immune systems are vital for survival.
• They protect organisms from infections, minimize damage from pathogens, and enable efficient resource management.
• They contribute to fitness and longevity in both plants and animals by maintaining health and facilitating reproduction.

Key Structures in Animals

• The immune system protects the body using specialized organs and cells.
• Bone marrow produces blood cells, including T-cell precursors and B-cells.
• Thymus is the site of T-cell maturation.
• Spleen filters blood and detects infections.
• Lymph nodes store and activate immune cells.
• Blood vessels transport immune cells.
• T-cells and B-cells are key immune cells involved in adaptive immunity.
• Primary lymphoid organs in animals: Bone Marrow produces T-cell precursors and B-cells; Thymus matures T-cells.
• Secondary Lymphoid Organs in Animals: Lymph Nodes store and activate T-cells and B-cells; Spleen filters blood to detect infections.

Cells of the Animal Immune System

• T-cells mature in the thymus and help fight infections.
• Helper T-cells (CD4+) activate other immune cells.
• Cytotoxic T-cells (CD8+) directly attack infected or cancerous cells.
• Regulatory T-cells (Tregs) maintain immune balance and prevent autoimmunity.
• B-cells are produced in bone marrow and involved in antibody production.

Key Structures in Plants

• Plants rely on innate immunity without adaptive memory, unlike animals.
• PAMPs (Pathogen-Associated Molecular Patterns) are recognized by plant immune receptors.
• PRRs (Pattern Recognition Receptors) detect PAMPs and trigger defense.
• Effectors are molecules from pathogens that try to suppress immunity.
• NLRs (Nod-like receptors) recognize effectors and activate stronger defense.
• Antimicrobial compounds are produced to fight off infections.
• Pattern-Triggered Immunity (PTI): PRRs detect PAMPs and trigger general defense (antimicrobial compounds).
• Effector-Triggered Immunity (ETI): NLRs recognize pathogen effectors, which result in a stronger immune response.
• Hypersensitive Response (HR): Infected plant cells self-destruct to stop pathogen spread.