Plant vs. Animal Immune Systems

• This module compares and contrasts the immune system processes in plants and animals
• Focus is given to organism immunity, particularly mammalian mechanisms
• Differences between plant and animal ways of resisting pathogen damage are highlighted

Immunity

• Immunity is the ability to resist damage from pathogens and harmful chemicals
• Microorganisms release toxins while cancer cells pose internal threats

Innate Immunity

• It is a fast-acting defense mechanism that responds quickly to infection
• Responses do not change with repeated exposure
• Specificity and memory are not present

Adaptive Immunity

• Slower responses occur at the beginning of an infection
• Exhibits memory and specificity, leading to faster response with subsequent exposure
• Pathogens are destroyed before symptoms develop

Innate Immune System Accomplishments

• Barrier defenses are the body's basic mechanisms to prevent and protect against chemicals entering
• Includes skin, epithelial surfaces, mucous membranes, and secretions like tears, saliva, and urine
• Internal defenses consist of chemical mediators, white blood cells, and inflammatory response
• Chemical mediators include antimicrobial proteins such as interferons and the complement system
• White blood cells include phagocytic cells and natural killer cells
• Inflammatory response releases chemical mediators that infect tissues
• Inflammation symptoms: fever, redness, swelling, pain, loss of function

Important Points on Epithelia and Inflammation

• Epithelia produce microbicidal substances and inhibits microbial growth
• Antibacterial enzyme lysozyme is secreted in tears and saliva
• Epithelial cells are held together by tight junctions to form a seal against external environment
• Acute inflammation activates immune response, whereas chronic inflammation leads to tissue damage

White Blood Cell Types

• Neutrophils are abundant white blood cells that are the first responders to microbial infection
• Eosinophils respond to multicellular parasites, releasing chemicals that perforates membranes
• Basophils initiate inflammatory responses by releasing histamine and heparin
• Basophils are common contributors to allergic responses
• Monocytes respond slower than neutrophils but last longer
• Monocytes differentiate into macrophages, that remain in the tissue that phagocytose and dendritic cells that present antigen fragments to lymphocytes
• Lymphocytes produce antibodies that target specific antigens, and are more common in the lymphatic system than blood

Adaptive Immune System

• This system recognizes traits of certain substances or antigens
• Antigens are parts of pathogens that generate an immune response
• Divided into foreign antigens from outside, and self-antigens that stimulate the body's immune system

Humoral Response

• It involves the production and secretion of antibodies by B-cells
• B-cells develop and mature in bone marrow
• They activate when encountering an antigen in the lymph nodes, that produce antibodies that recognizes only one kind of antigen

Antibodies Secretion

• Antibodies are secreted by B-cells in the bloodstream, or displayed on the surfaces of some cells
• Antibodies are ready to combat extracellular pathogens
• Adaptive immune response is activated by the presence of foreign substances on pathogens
• Drugs/therapeutic agents can attach to antibodies specific for cancer cell antigens, avoiding damage to healthy tissue
• Vaccines contain adjuvants which activate the innate immune response
• Protein antigen from the pathogen or an inactivated version stimulates B cells to produce antibodies

Cell Mediated Response

• Immune response occurs when cytotoxic cells defend the body against microorganisms inside body cells
• Focuses on pathogens not easily accessible
• Uses antibodies by B-cells
• Some pathogens are found inside cells such as viruses
• Due to the production of T-cells

T-Cells

• White blood cells produced in the bone marrow that mature in the thymus
• Activated when encountering antigens in lymph nodes
• Needed to recognize an antigen from self-molecules
• MHC molecules are glycoproteins that have binding sites for antigens

Types of T-Cells

• Cytotoxic T cells: recognize and kill virus-infected cells
• Helper T cells: help immune cells to survive and perform functions by secreting proteins
• Regulatory T cells: control immune responses by turning them off
• Prevent the immune system from harming the body
• Loss of function can lead to autoimmune disease

Invertebrates Immune System

• Plants and invertebrate metazoans have only an innate immune system
• Free circulating cells (hemocytes) are responsible for cell-mediated immunity
• When activated, hemocyte types perform phagocytosis, reactive oxygen species production
• Leads to release hydrolytic enzymes and antimicrobial peptides release

Metschnikow and Phagocytosis

• Metschnikow 1st saw cells digesting bacteria while studying starfish
• The process he called eating of cells" by other cells is known as "phagocytosis"
• Invertebrates are complex

Plant Defense

• Plants sustain and defend themselves, by use either growth mode or defense mode
• Plants display innate immune system, but does not exhibit immune cells or antibodies
• All plant cells have immune capabilities via two basic immune pathways
• These pathways include recognition receptor, and signaling pathways

Plant Cell Immunity

• A pattern recognition receptor (PRR) on the plant cell's surface recognizes pathogen-associated molecular patterns (PAMPs) released by invaders
• Signaling pathways inside the cell spur production of reactive oxygen species (ROS) and antimicrobial compounds to combat the pathogen
• PAMP-triggered pathways can lead to changes in gene expression and hormone levels

Plant Unique Protection

• Plants have diverse chemical defenses limiting damage from bacteria, fungi, worms, or insects
• Organic compounds are produced as secondary metabolites and do not affect vegetative growth/development

Chemical Compounds Functions for Plant Defense

• Alkaloids: Biosynthesized in roots, involved in defense against insect herbivory
• Phenolics: Repel herbivores, inhibit enzymes, attract pollinators, absorb UV radiation, decrease competition
• Terpenoids: Act like active compounds in resin or volatiles, can modify development in herbivores
• Jasmonic acid regulates defense responses against insects
• Salicylic acid has a major role in mediating defense, essential for induction of defense responses
• Sulfur is crucial for planting development, maintenance, and resistance to environmental stress

Plant Immune Interference

• Plants interfere with growth when needing a defense from pathogens
• Many species power down immune systems at night when growing ramps up
• They lower immunity during changes of temperature, humidity, & light exposure
• Relies on a plant's microbiota below and above the soil

Plant Immunity Research

• According to research, plant cells read copies when switching from growth to defense mode
• Copies of defensive protein genes have a special signal
• This special signal tells the cell to only read that copy when a pathogen is around
• Putting the special signal can increase quick response to infections