Biology Immunology Overview

Non-Specific Responses to Infection

• Cell Recognition: The body's ability to distinguish between "self" and "non-self" cells is crucial for preventing illness. Cells of different organisms have unique proteins, like glycoproteins in cell membranes, that help with recognition.
• Leucocytes and Types: These cells, formed in bone marrow, defend against infection. They can change shape to squeeze through blood vessels. Some have granules (granulocytes), including neutrophils (most common, engulf and digest pathogens), eosinophils (fight parasites, involved in inflammation), and basophils (produce histamines, involved in inflammation). Others lack granules (agranulocytes), like monocytes that mature into macrophages which engulf and destroy pathogens through phagocytosis, and lymphocytes which are involved in specific responses.

Non-Specific Responses

• Inflammation: A localized response to infection, characterized by heat, redness, swelling, and pain. Mast cells release histamines causing blood vessels to dilate, allowing more blood flow to the infected area.
• Fever: The body raises its temperature to slow pathogen reproduction. Many pathogens reproduce faster at normal body temperatures. A higher temperature helps specific immune responses function more effectively.
• Phagocytosis: Cells (like neutrophils and macrophages) engulf and destroy pathogens. Lysosomes are key for breaking down pathogens.

Interferons

• Interferons: Cells invaded by viruses release chemicals called interferons that block viral replication in other cells. This hinders virus reproduction. Interferons diffuse to other cells, rendering them resistant to infection.

Specific Immune Response

• The main types of lymphocytes*

• B-cells: Produced in bone marrow; produce antibodies (immunoglobulins) that recognize and bind to specific pathogens. When bound to an antigen, B-cells create plasma cells to produce antibodies, and B-memory cells which provide immunological memory.

• T-cells: Produced in bone marrow, activated in thymus gland. They have receptors that bind to antigens on body cells. This allows them to identify infected cells, cancer cells, or cells that pose threats to body tissue. T-killer cells destroy infected cells, releasing chemicals to trigger cell death. T-helper cells activate other immune cells (other T-cells, B-cells), leading to an effective immune response, and T-memory cells give lasting immunological memory to the body.

The Humoral Response

• Helper T-cell Activation: When pathogens enter the body, phagocytes attract T-helper cells. Macrophages engulf pathogens, and display/combine the antigen with MHC molecules, presenting the complex on the outer membrane. T-cells receptors bind to the complex activating the immune system. This creates clones of active T-helper cells + T-memory cells, granting long-lasting immunological memory, which produce immunoglobulins (antibodies).
• Effector Stage: The antigens from the pathogen are seen by the cells through MHC receptors. The T-helper cells initiate the formation of plasma cells by B-cells, which synthesize and release large quantities of antibodies. The antibodies bind to the pathogen which labels it for phagocytosis and elimination.

The Cell-mediated Response

• Cell-mediated Response: Involves T-killer cells which act on infected body cells. By identifying infected cells, T-killer cells and releasing enzymes will destroy infected body cells which limits the spread of harmful pathogens.

Primary and Secondary Immune Response

• Primary Response: The body's initial response to an infection involving a pathogen take a relatively longer period of time.
• Secondary Response: The body's faster response to the same pathogen in a subsequent infection. Immune cells "remember" the pathogen, making the response quicker and more effective. This involves the creation of T-memory and B-memory cells.

Developing Immunity

• Natural Immunity: Natural active immunity is when the body encounters a pathogen and activates its immune response. Natural passive immunity involves receiving antibodies from another source, like a mother to a fetus through the placenta, or through breastfeeding.
• Artificial Immunity: Artificial active immunity involves exposure to a safer form of the pathogen (e.g., vaccines). Artificial passive immunity involves receiving antibodies from another source (e.g., antibodies from blood serum).

Eradication, Elimination, and Control of Disease

• Eradication: The complete removal of a disease from the population, eliminating it from all environments.
• Elimination: Similar to eradication, but is not possible to remove completely from all environments.
• Control: Reducing the incidence of disease to acceptable levels.

Herd Immunity

• Herd Immunity: Occurs when a large percentage of a population is vaccinated. It offers protection to individuals who cannot be vaccinated.

Antibiotics

• Antibiotic Action: Antibiotics have two effects; bacteriostatic agents stop the growth of bacteria, while bactericidal agents kill bacteria.
• Antibiotic Resistance: Bacteria can develop resistance to antibiotics through mutations. This results from overuse and inappropriate use of antibiotics.

Antibiotic resistance

• Factors influencing antibiotic effectiveness: The concentration of the drug around infected areas, pH, host and pathogen cell, and the susceptibility of the pathogen to the antibiotic used.
• Antibiotic resistance: Occurs when pathogens develop resistance to the antibiotics that were used to treat the pathogen, and therefore the drug is ineffective.

Hospital-acquired Infections (HAIs)

• Causes & prevention: HAIs are infections acquired in hospitals. Prevention involves hand hygiene, isolation of infected patients, controlling the use of antibiotics and monitoring for HAIs.