Brief Summary
This video provides a comprehensive summary of immunity, covering key aspects such as types of microbes, lines of defence, the difference between innate and adaptive immunity, the roles of different immune cells, the concepts of self and non-self, hypersensitivity, and methods of boosting immunity through vaccination and serum therapy.
- Microbes are categorised into bacteria, viruses, fungi, and parasites, with examples provided for each.
- The body's defence mechanisms are divided into three lines: physical barriers, inflammatory response, and specific immune responses (humoral and cellular).
- Vaccination involves injecting weakened or inactive pathogens to stimulate antibody production, while serum therapy provides ready-made antibodies for immediate protection.
Introduction to Immunity and Microbes
The video begins by defining microbes as microscopic organisms found everywhere, some beneficial and others harmful. Viruses are noted as non-living outside of cells, requiring a host to survive. Microbes are categorised into four main types: bacteria (e.g., Bacillus Koch causing tuberculosis and Escherichia coli in the colon), viruses (e.g., coronavirus and influenza), fungi (e.g., yeast and bread mould), and parasites (e.g., Paramecium and Plasmodium causing malaria). It's important to know these types and examples. Microbes can multiply rapidly under favourable conditions like available food, moisture, and a temperature of around 37°C.
Classification of Microbes: Pathogenic vs. Non-Pathogenic
Microbes are classified as either pathogenic (disease-causing) or non-pathogenic. Examples of pathogenic microbes include Bacillus Koch, viruses (influenza, coronavirus), and Plasmodium. Non-pathogenic microbes include E. coli and yeast. Some microbes, like bread mould, can be both pathogenic (when consumed on spoiled food) and non-pathogenic (used in medicine production). Due to the abundance of microbes, the human body has defence mechanisms to prevent their invasion and proliferation.
Lines of Defence: An Overview
The body's defence mechanisms are divided into three lines. The first line of defence consists of physical barriers. The second line is the inflammatory response, including phagocytosis. The third line involves specific immune responses, both humoral and cellular. The first two lines are non-specific, acting against any invading microbe, while the third line is highly specific, targeting particular types of microbes.
First Line of Defence: Physical Barriers
Physical barriers are categorised into chemical, mechanical, and biological types. Chemical barriers include tears, nasal mucus, saliva, sweat, semen, vaginal secretions, and stomach acid, which contain enzymes that kill microbes. Mechanical barriers include skin, cilia, and eyelashes, which physically expel or prevent microbes from entering. Biological barriers involve living organisms, such as non-pathogenic bacteria in the colon.
Second Line of Defence: The Inflammatory Response
The inflammatory response is triggered when physical barriers are breached, such as through a wound. Symptoms include swelling, redness, heat, pain, and pus formation. Pain is due to the stimulation of nerve endings by swelling. Swelling results from plasma leaking from blood capillaries into the affected area. Redness and heat are caused by dilated blood vessels and increased blood flow. Pus is a collection of dead microbes and white blood cells. Phagocytosis, carried out by phagocytes, is a key part of this response, involving the engulfment and digestion of microbes.
Phagocytosis: The Process
Phagocytosis involves several stages: attraction and attachment, engulfment (forming pseudopods), ingestion, digestion (fusion with lysosomes containing digestive enzymes), and excretion of waste products. Phagocytes are non-specific, capable of engulfing various types of microbes.
Third Line of Defence: Specific Immune Responses - Introduction
When phagocytosis is insufficient, the third line of defence, involving specific immune responses, is activated. Key terms include antigens (foreign substances triggering an immune response) and antibodies (proteins targeting specific antigens). Lymphocytes, specifically B cells and T cells, are responsible for these responses. B cells mediate humoral immunity, while T cells mediate cellular immunity.
Humoral Immunity: B Cells and Antibody Production
Humoral immunity is activated when microbes, such as bacteria, release toxins (toxins) that circulate in the blood or lymph. B cells recognise the antigen, proliferate, and differentiate into memory B cells and plasma cells. Plasma cells produce antibodies specific to the antigen, neutralising it and preventing its spread. The antigen-antibody complex is then phagocytosed by phagocytes. Toxoids, treated and non-pathogenic toxins, are important in vaccines.
Cellular Immunity: T Cells and Infected Cells
Cellular immunity is activated when microbes, like viruses, infect cells and replicate inside them. T cells recognise infected cells and differentiate into cytotoxic T cells (Tc) and memory T cells. Cytotoxic T cells kill infected cells, preventing further spread of the microbe.
Comparison of Humoral and Cellular Immunity
A table compares humoral and cellular immunity. Humoral immunity involves antibodies, B cells, and targets toxins or microbes circulating in the blood or lymph, resulting in neutralisation of the antigen. Cellular immunity involves cytotoxic T cells, T cells, and targets infected or cancerous cells, resulting in their destruction.
Self vs. Non-Self: The ABO Blood Group System
The body distinguishes between self and non-self through the ABO blood group system and molecules on cell membranes. The ABO system involves four blood types: A, B, AB, and O, based on the presence of A and B antigens on red blood cells. Blood transfusions must be compatible to avoid agglutination (clumping) caused by antibodies reacting with foreign antigens. Type O is a universal donor, and type AB is a universal recipient.
The Rhesus (Rh) Factor and Blood Transfusions
The Rhesus (Rh) factor (+ or -) further determines blood type compatibility. Rh-negative individuals can donate to Rh-positive individuals, but not vice versa. Examples illustrate how to determine blood transfusion compatibility using ABO and Rh factors.
Determining Blood Types and Transfusion Compatibility: Worked Examples
The video provides worked examples of determining blood types based on agglutination reactions with anti-A, anti-B, and anti-D antibodies. It also demonstrates how to determine which individuals can donate blood to a recipient with a specific blood type.
Grafting and Transplants: Understanding Self and Non-Self
Grafting involves transplanting cells or tissues from one individual to another or from one part of the body to another. The body recognises cells as self or non-self based on surface markers. Grafts from the same individual or identical twins are usually accepted due to matching markers. Grafts from unrelated individuals are often rejected due to mismatched markers, triggering an immune response.
Hypersensitivity (Allergy): An Overreaction of the Immune System
Hypersensitivity, or allergy, is an exaggerated immune response to harmless substances. Symptoms include allergic rhinitis, skin rashes, swelling, asthma, and eczema. Common allergens include dust, pollen, mites, chemicals, and animal dander.
Mechanism of Allergy: Histamine Release
The mechanism involves initial exposure to an allergen, leading to B cell activation and production of IgE antibodies. IgE antibodies bind to mast cells. Upon subsequent exposure, the allergen binds to IgE on mast cells, triggering the release of histamine and other chemicals, causing allergic symptoms. Antihistamines can prevent histamine release, alleviating symptoms.
Boosting Immunity: Vaccination and Serum Therapy
When the immune system is unable to combat severe infections, assistance is provided through vaccination or serum therapy. Vaccination involves injecting weakened or inactive antigens to stimulate antibody production. Serum therapy involves providing ready-made antibodies for immediate protection.
Vaccination: Types of Vaccines and the Importance of Boosters
Vaccines can contain live attenuated microbes, killed microbes, toxoids, or antigenic molecules. Booster shots are important to increase antibody levels and provide long-term immunity. The video analyses graphs showing antibody levels after initial vaccination and booster shots, highlighting the faster and stronger response after the booster.
Serum Therapy: Providing Ready-Made Antibodies
Serum therapy involves injecting serum containing ready-made antibodies. An example is given of a horse injected with diphtheria toxoid, producing antibodies that are then extracted and injected into a person infected with diphtheria.
Vaccination vs. Serum Therapy: A Comparison
A table compares vaccination and serum therapy. Both are specific to certain antigens. Vaccination involves injecting weakened antigens, resulting in a slow but long-lasting immune response for prevention. Serum therapy involves injecting ready-made antibodies, resulting in an immediate but temporary immune response for treatment.
