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Immunity
Definition
‘immunity’ is defined as resistance exhibited by the host against any foreign antigen including microorganisms i.e the body’s ability to resist or fight off foreign substances, such as microorganisms (like bacteria or viruses), that can cause diseases. It’s like the body’s defense system that helps protect us from getting sick. There are two types of immunity Innate immunity Acquired immunity
Innate immunity
Definition
Innate immunity is the natural resistance that a person has from birth. It’s based on our genetic and physical characteristics. This type of immunity doesn’t require prior exposure to specific germs (antigens) to work.
Types of Innate Immunity
Species immunity Species immunity refers to the resistance to certain pathogens exhibited by all members of a particular species. Example: Some pathogens may infect humans but not chickens due to physiological and biochemical differences between species. Racial immunity Racial immunity describes differences in susceptibility or resistance to infections among different races or populations within the same species. Example: certain human populations may show differences in susceptibility to diseases like tuberculosis based on genetic or socioeconomic factors. Individual Immunity Individual immunity refers to variations in resistance to infections among individuals of the same race and species.
Mechanisms of innate immunity
Epithelial Surfaces
(i) Skin: Acts as a barrier against microorganisms and produces substances like sweat and sebum that can kill bacteria. Normal bacteria on the skin protect against invaders, but disturbances can lead to infections. (ii) Respiratory Tract: Mucous membranes in the nose and lungs trap particles, which are then cleared out by coughing or swallowing. Phagocytes in the lungs can also ingest invaders. (iii) Intestinal Tract: Saliva and stomach acid destroy bacteria. Good bacteria in the gut prevent harmful bacteria from colonizing. (iv) Conjunctiva: Tears flush away bacteria, and tears contain lysozyme, which kills bacteria. (v) Genitourinary Tract: Urine flow flushes out bacteria. Vaginal acidity (due to bacteria) prevents infection in females, and semen may have antibacterial properties in males. Antibacterial Substances: Blood and Tissues: Various substances like complement, lysozyme, and interferons have antibacterial or antiviral effects. Complement is especially important in destroying invading microorganisms. Cellular Factors (i) Phagocytes: Cells like neutrophils and macrophages ingest and destroy pathogens through a process called phagocytosis. (ii) Natural Killer (NK) Cells: Lymphocytes that target viruses and tumors. Inflammation: Response to Injury: Inflammation is triggered by injury or infection. It involves increased blood flow, leaky blood vessels, and immune cell infiltration to fight off pathogens and promote healing. Fever Natural Defense: Elevated body temperature helps kill pathogens and stimulates immune responses, including interferon production to combat viruses. Acute Phase Proteins: Response to Infection: Certain proteins increase during infection, aiding in complement activation and tissue repair to limit damage and promote healing.
Acquired immunity
The resistance acquired by an individual during life is known as acquired immunity. It is of two types,
Cell-Mediated Immunity (CMI):This immunity relies on T-lymphocytes (T cells) that are specifically activated against antigens. Process: T-Cell Activation: T cells become sensitized (activated) when they encounter specific antigens presented by antigen-presenting cells (APCs). Types of T Cells: (i) Cytotoxic T Cells (CD8+): Destroy infected or abnormal cells by directly killing them. (ii) Helper T Cells (CD4+): Coordinate immune responses by secreting cytokines that activate other immune cells. (iii) Memory T Cells: Like memory B cells, memory T cells remember specific antigens for future encounters. Role in Immune Defense: (i) Chronic Infections: Cell-mediated immunity is crucial in combating chronic bacterial infections (e.g., tuberculosis, leprosy) where pathogens can survive inside cells. (ii) Viral Infections: T cells are essential for eliminating virus- infected cells. Humoral and cell-mediated immunity work together to provide comprehensive protection against pathogens. While antibodies play a key role in neutralizing extracellular pathogens and toxins, T cells are critical for combating intracellular infections and coordinating immune responses. Both humoral and cell-mediated immune responses generate memory cells, ensuring long-lasting immunity upon re- exposure to the same antigen.
Passive Immunity
Passive immunity occurs when an individual receives preformed antibodies rather than producing them through their own immune response. Passive immunity is short-term and does not confer lasting immunity like active immunity. There are two types of passive immunity Natural passive immunity Artificial passive immunity Natural Passive Immunity Transfer from Mother to Infant. Maternal antibodies are transferred to the fetus through the placenta during pregnancy. Maternal antibodies are also passed to the infant through breast milk (colostrum) after
birth. This provides temporary protection to the newborn until their own immune system matures. Artificial Passive Immunity Administration of Antibodies it Involves injecting preformed antibodies (antibody-containing preparations) into a non-immune individual. Sources of artificial passive immunity include: Hyper immune sera from animals or humans. Convalescent sera (from recovering patients) with high levels of specific antibodies. Pooled human gammaglobulin containing antibodies against certain infections. Methods and Examples Hyper immune Sera: Example: Antitetanus serum (ATS) prepared from horses injected with tetanus toxoid. Human ATS is used to reduce allergic reactions. Convalescent Sera: Used for passive immunization against measles, rubella, and other diseases. Pooled Human Gammaglobulin: Used against viral infections like hepatitis A. Uses of Passive Immunization: Immediate Protection: Provides rapid but temporary protection in non-immune individuals facing serious infections. Suppression of Harmful Immune Responses: Used to prevent immune reactions that could be harmful, such as Rh immunoglobulins given to Rh-negative mothers after delivery to prevent immune response to Rh factor in Rh-positive babies. Treatment of Infections: Passive immunization can be used as a treatment for serious infections when immediate immunity is needed.
