Anaphylaxis: A severe and possibly fatal allergic response.
Antigen: Cells, organisms, or structures on a cell membrane that are foreign to the body. In a healthy animal, the presence of an antigen will stimulate an immune response.
Antibody: Also known as immunoglobulins; proteins produced by plasma cells in response to antigens. Antibodies are specific to a certain antigen.
Autoimmune Disease: An abnormal disease process where the body identifies its own cells as foreign and starts an immune response.
Immunization: The process of stimulating an immune response by administering (or inoculating) an animal with a vaccine. The immune response is similar to the response that would occur through natural disease.
Overview
Immunology: The study of the immune system.
Main Function of the Immune System: To protect the body from damage or disease by identifying self and non-self. Once a non-self or foreign invader is identified, the body can utilize various methods to remove or destroy the invader, including:
Phagocytosis and destruction of foreign cells.
Lysis of foreign cell membranes.
Inactivation of pathogenic organisms or chemical substances.
Precipitation or clumping of cells or molecules.
Excessive Reaction: If the reaction to a foreign invader is excessive, it can injure the body's cells as well as the invader, resulting in anaphylaxis.
Autoimmune Diseases: Occur when the body mistakenly identifies self as non-self.
Innate (Non-specific) Immunity
Definition: Strives to eliminate all threats to the body and is not specific to any one type of threat.
**Examples of Innate Immunity:
Skin: Physical barrier against microbes.
Saliva and Gastric Acid: Destroys/inhibits bacteria and viruses.
Tears: Rear alike its function in destroying/inhibiting bacteria and viruses.
Turbinates/Mucociliary Escalator: Cells lining the respiratory tree are covered with cilia and mucus; these trap microorganisms and prevent them from invading lung tissue.
Bodily Functions: Sneezing, urination, and coughing work to expel pathogens.
Inflammation:
Inflammatory mediators are proteins produced by damaged cells, white blood cells, and complement.
They cause blood vessel dilation, increase blood flow to affected areas, and make vessel walls "leaky" to allow plasma and white blood cells into tissues.
Induce fever to inhibit pathogen growth.
Phagocytosis: Cells such as neutrophils, macrophages, monocytes, and dendritic cells engulf and digest pathogens.
Natural Killer (NK) Cells: Circulate through the body, seeking abnormal proteins that may indicate sick or cancerous cells for destruction.
Interferon: Inhibits virus growth and modulates the immune system.
Complement Cascade: A group of proteins that circulate in inactive forms and are activated upon encountering a pathogen. Functions include:
Opsonization: Coats pathogens to facilitate phagocytosis by macrophages.
Mast Cell Activation: Induces release of histamine and amplifies inflammation.
Membrane Attack Complex (MAC): Causes rupture of pathogen cell membranes.
Adaptive (Specific) Immunity
Definition: Immunity designed to target specific antigens and can be referred to as acquired immunity.
Interaction with Innate Immunity: Specific immunity collaborates with innate immunity, relying on both systems for optimal function.
Components of Specific Immunity: Two main responses:
Cell-Mediated Immunity:
Involves T-cells (lymphocytes) that react to antigens presented by Antigen Presenting Cells (APCs), which often are macrophages and dendritic cells.
Functions include:
Cytotoxic T-cells: Destroy cells displaying the antigen.
Helper T-cells:
Release cytokines to stimulate migration of white cells and enhance macrophage function.
Assist B-cells in activating to produce antibodies.
Guide NK cells.
Suppressor T-cells: Reduce antibody formation and immune response to prevent autoimmune diseases and assist in immune memory by preventing a rapid response that could overwhelm the immune system.
Memory Cells: Long-lasting T cells that respond more rapidly to subsequent exposures to antigens.
Humoral Immunity:
Involves B-cells that bind to antigens either directly or with assistance from Helper T-cells.
Upon activation, B-cells can:
Differentiate into plasma cells generating antibodies.
Phagocytize pathogens and present antigens to Helper T-cells.
Memory cells from B-cells also persist in circulation for rapid response upon re-exposure to the antigen.
Antibodies
Definition: Proteins produced by B-cells, acting in immune response by binding to specific antigens.
Classes of Antibodies:
IgG: Most prevalent antibody; crosses the placenta and forms ~75% of circulating immunoglobulins. Produced after IgM, plays a crucial role in colostrum.
IgM: First antibody formed in response to infection and by newborns; constitutes about 5% of immunoglobulins.
IgA: Predominantly in mucosal areas (saliva, tears, mucus); represents ~20% of immunoglobulins, important for mucosal barriers.
IgE: Found mainly in basophils and mast cells; involved in allergic and parasitic responses, present in small amounts.
IgD: Function poorly understood; present on B-cell surfaces in trace amounts.
B-cells' Flexibility: B-cells can produce different types of antibodies and even switch types during infection.
T and B Cell Origins and Locations
Naming Origin:
T-cells: Named for their maturation in the thymus.
B-cells: Named after the Bursa of Fabricius in birds where they were first identified; in mammals, they originate from the bone marrow.
Location in Body:
T-cells: Predominantly circulate in blood.
B-cells: Mostly reside in lymphatic organs (lymph nodes, spleen, tonsils).
Immune System Function Overview
The immune system ensures proper distinction between self and non-self, crucial in avoiding autoimmunity.
Hypothetical Pathogen Interaction
Analogy: A scoop of ice cream covered with various toppings represents a pathogen.
Antigen Examples:
Sprinkles, peanut pieces, and cherries may serve as antigens.
Epitopes: Different variations on these toppings represent epitopes.
White Blood Cell Interaction with Pathogens
Recognition of Self vs Non-Self: White blood cells must identify self to prevent autoimmunity.
Epitope Specificity of T-cells and B-cells: Each T-cell and B-cell is specific to a single epitope, activated only upon recognizing that epitope.
Immune Response Scenario: "Darby and the Ice Cream Sundae"
Initial Exposure: "Darby", a puppy, encounters a vanilla ice cream sundae (pathogen).
Macrophages phagocytize the sundae and present its antigens.
Neutrophils and T-cells respond to chemical signals from inflamed tissues.
Specific Immune System Activation:
Activated T-cells differentiate into various functional types (helper, cytotoxic, memory, suppressor).
Helper T-cells attract B-cells that recognize the same antigens, leading to antibody production, primarily IgM first and then IgG.
Antibodies attach to pathogens, aiding in their destruction and creating easier targets for phagocytes.
Regulation by Suppressor Cells: Once the infection is controlled, suppressor cells help regulate and reduce the immune response.
Memory Cell Formation: T-memory and B-memory cells circulate and provide faster responses upon future encounters with the same pathogen.
Passive Immunity
Definition: Immunity obtained from an external source, such as antibodies from the mother.
Colostrum: Vital early nursing liquid for newborns, providing necessary antibodies against known pathogens, requiring timely consumption post-birth (1-18 hours).
Hyperimmunized Serum: Treatment using serum rich in antibodies against a specific illness can enhance recovery (e.g., parvovirus).
Antitoxins and Antivenoms: Provide antibodies against specific toxins or venoms, used in emergencies.
Active Immunity
Definition: Immunity developed after exposure to pathogens, through natural infection or vaccination.
Vaccine-Induced Immunity: Simulated responses to non-pathogenic versions of organisms promote memory development for future encounters.
Vaccine Types
Core vs Non-Core Vaccines:
Core vaccines are recommended universally based on species and age.
Non-core vaccines are tailored to individual animal needs.
Infective Vaccinations: Mimic real pathogens but do not cause disease; stimulate a robust immune response but carry a small risk of reverting.
Non-infective Vaccinations: Do not invade host cells; often require adjuvants to bolster immune response, but may be linked to inflammatory issues.
Vaccine-Related Terms
Adjuvanted: Vaccines with added adjuvants.
Non-adjuvanted: Vaccines without adjuvants.
Attenuated: Modified organisms that do not cause disease, could be fully or partially killed.
Recombinant: Vaccines modified at the DNA level to enhance immune responses.
Sub-unit: Composed of purified segments of pathogens rather than whole cells.
Vectored: Utilize harmless viruses carrying genetic material from pathogenic organisms to stimulate an immune response.