Immune Systems in Plants & Animals

Immune System in Plants & Animals

• The immune system recognizes and protects organisms from pathogens (foreign structures and molecules).
• An appropriate immune response is produced.
• The immune system in both plants and animals has innate and adaptive components.
• Innate immunity is inherited and provides immediate nonspecific defense.
• Adaptive immunity is acquired and involves more complex, antigen-specific responses.
• Plant and animal immune systems have differing complexities and mechanisms.

Pathogens

• Pathogens are microorganisms that cause diseases.
• Communicable diseases can spread from one organism to another.
• Four main types of pathogens are bacteria, fungi, viruses, and protists.

Plant Immune System Mechanisms

• Plants defend against pathogens using innate mechanisms activated upon pathogen detection.
• Physical barriers like a waxy cuticle, thick cell walls (preventing entry), thorns, and trichomes deter pathogens and herbivores.
• Protective outer coverings such as bark, made of layers of dead cells.
• Antimicrobial compounds (phytoalexins and defensins) inhibit pathogen growth.
• Secondary metabolites (alkaloids, phenolics) deter herbivores and defend against infections.

Animal Immune System Mechanisms

• Animals have a dual immune system, combining innate and adaptive immunity.
• Innate immunity includes first line defenses (skin, mucous membranes, secretions) and second line defenses (phagocytic leukocytes, antimicrobial proteins, inflammatory response, fever).
• Adaptive immunity has a third line of defense characterized by lymphocytes, antibodies, and memory cells.
• Phagocytic leukocytes (white blood cells) fight foreign material like bacteria and viruses.
• Antimicrobial proteins directly kill pathogens by disrupting membranes, interfering with processes, or inhibiting essential molecules.

The Immune System (Diagram)

• The innate immune system has physical barriers (skin, organ mucosal layers) and chemical barriers (stomach acid, lysozymes).
• The innate system also has an inflammatory response (mast cells, neutrophils, macrophages, natural killer cells)
• The adaptive immune system has cell-mediated response (T-lymphocytes) and humoral response (B-lymphocytes).
• Both systems have immune system linkage (dendritic cells).
• Adaptive immunity produces CD4+ and CD8+ T-cells and antibodies.

Adaptive Immune System Response

• Adaptive immunity provides a more specialized and targeted attack against specific pathogens.
• It has "memory," enabling a more efficient response upon future exposure.
• B cells produce antibodies binding to antigens (foreign molecules).
• Helper T cells activate B cells and other immune cells.
• Cytotoxic T cells kill infected cells directly.
• Memory cells provide faster responses upon later encounters with a pathogen.

Adaptive Immune System Challenges

• The immune system struggles to fight pathogens that quickly change their surface proteins or hide within cells.
• HIV infection is an example as it quickly changes its surface proteins to evade detection, making it hard for the body to eliminate.

Key Differences Between Plant and Animal Immune Systems

• Animals have adaptive immunity; plants lack this.
• Plants rely on broad-spectrum resistance using systemic signals (thick cell walls, waxy cuticle, bark, trichomes).
• Animal immunity uses mobile immune cells (macrophages, T cells, B cells) moving to infection sites.

Roles of Immune System in Survival of Plants and Animals

• Plant and animal immune systems are crucial for survival by protecting against pathogens, preventing disease spread, providing adaptation, enabling immunity, defending against environmental stress, repairing tissues, and contributing to ecosystem stability.