The immune system, a complex network of cells and proteins, protects the body against infection. This involves the innate and adaptive immune responses, with specific functions and cell types engaged in each response.
Innate Immune Response
Physical and Chemical Barriers
- Skin: The outermost barrier that prevents pathogens from entering the body.
- Mucous Membranes: Line body cavities and secrete mucus to trap pathogens.
- Saliva and Tears: Contain enzymes that break down bacterial cell walls.
- Acidic Environment in the Stomach: Kills many ingested bacteria.
Understanding the role of carbohydrates and lipids in the body can further illuminate how the immune system is supported by nutrition.
Cellular Components
- Neutrophils: The most common phagocytes, are among the first responders to an infection.
- Macrophages: Engulf pathogens and dead cells, display antigens to T cells, and release cytokines.
- Dendritic Cells: Present antigens to T cells, linking innate and adaptive immune responses.
- Natural Killer Cells: Recognise and kill infected or cancerous cells.
Protein structure plays a critical role in the functionality of these immune cells, especially in the recognition and response to pathogens.
Inflammatory Response
- Signs of Inflammation: Redness, heat, swelling, and pain.
- Chemicals Involved: Histamine increases blood vessel permeability, cytokines attract immune cells.
- Role of Neutrophils and Macrophages: Engulf pathogens, dead cells, and debris.
Adaptive Immune Response
Introduction to Adaptive Immunity
Adaptive immunity is more complex, specific, and has a memory component that innately responds.
Lymphocytes: T and B Cells
- T Cells:
- Helper T Cells: Stimulate B cells and cytotoxic T cells; secrete cytokines.
- Cytotoxic T Cells: Kill infected cells by inducing apoptosis.
- Regulatory T Cells: Suppress immune reactions to self-antigens.
- B Cells: Produce and secrete antibodies that are highly specific to an antigen.
The structure and function of the heart are essential to understand as it plays a vital role in circulating immune cells throughout the body.
Antibody Production and Structure
- Antibodies: Y-shaped proteins that have two antigen-binding sites.
- Memory B Cells: Remain to provide quicker response to future infections.
- Plasma Cells: Secrete antibodies into blood and lymph.
Memory Cells and Immunity
- Memory T Cells: Long-lived; provide immunity to previously encountered infections.
- Primary and Secondary Immune Responses: Secondary is faster due to memory cells.
Human Leukocyte Antigen (HLA) System
- Role in Self-Recognition: Helps immune system distinguish self from non-self.
- Importance in Transplants: Matching HLA between donor and recipient minimises rejection.
The structure and function of the digestive system are crucial in providing the necessary nutrients that support the immune system.
Roles of Different Leukocytes
- Neutrophils and Macrophages: Innate immunity; engulf pathogens.
- Eosinophils: Combat parasitic infections; involved in allergies.
- Basophils: Release histamine; involved in allergic responses.
- Lymphocytes: Adaptive immunity; T cells regulate, B cells produce antibodies.
Exploring the structure and function of the respiratory system can help understand its role in defending against airborne pathogens.
Vaccination and Immunity
- Vaccine Types: Live-attenuated, inactivated, subunit, and conjugate vaccines.
- Herd Immunity: Protects those who cannot be vaccinated.
Challenges and Issues
- Autoimmune Diseases: Rheumatoid arthritis, lupus, and Type 1 diabetes.
- Immunodeficiency Disorders: HIV/AIDS weakens the immune system.
- Allergies: Hay fever, asthma, and eczema; overreaction to harmless substances.
- Ethical Considerations: Individual vs. community rights in vaccination policies.
FAQ
Cytokines are small proteins produced by immune cells that act as chemical messengers. They play a central role in coordinating the immune response by promoting communication between cells. For example, cytokines can stimulate the proliferation and differentiation of immune cells, direct them to the site of infection, and regulate inflammatory responses. They enable a targeted and effective immune response, guiding various cells to work in concert to eliminate pathogens. Different cytokines have specific functions, and their balanced action is crucial for a proper immune response.
The complement system is a part of the innate immune response, comprising over 30 proteins found in blood plasma. These proteins interact in a cascade manner to opsonise pathogens, making them easier for phagocytes to engulf, and to create pores in the membranes of pathogens, causing lysis. The complement system also enhances inflammation by attracting immune cells to the site of infection. It works in conjunction with antibodies and phagocytes to clear pathogens, bridging the innate and adaptive immune responses.
Natural killer (NK) cells are part of the innate immune response and can identify infected or cancerous cells through the lack of specific surface molecules called Major Histocompatibility Complex (MHC) class I. Healthy cells express MHC class I molecules, which signal to the NK cells that they are normal. Infected or cancerous cells often have reduced MHC class I expression, allowing NK cells to recognise and target them. Thus, the presence or absence of these molecules helps NK cells discriminate between healthy and abnormal cells.
Allergies are overreactions of the immune system to harmless substances like pollen or pet dander. In an allergic reaction, the immune system mistakenly identifies these substances as threats, leading to the production of IgE antibodies. Upon subsequent exposure, these antibodies trigger mast cells to release histamine and other chemicals, causing symptoms like swelling, redness, and itching. The immune system's misidentification of a non-harmful substance as a threat leads to this inappropriate and exaggerated response.
Memory cells are crucial in vaccination as they provide long-term immunity against specific pathogens. When a vaccine introduces a harmless part of a pathogen, the immune system responds by producing memory B and T cells specific to that pathogen's antigens. If the individual is later exposed to the actual pathogen, these memory cells rapidly activate a secondary immune response, producing antibodies and killing infected cells more quickly and effectively. The presence of memory cells allows the body to recognise and combat previously encountered pathogens more efficiently, thus providing immunity.
Practice Questions
The innate immune response is the body's first line of defence, providing a rapid but non-specific reaction to all pathogens. It involves physical barriers like skin and mucous membranes, and cellular components like neutrophils and macrophages that engulf pathogens. In contrast, the adaptive immune response is slower, specific, and relies on B and T lymphocytes. T cells regulate immune reactions, while B cells produce antibodies specific to antigens. Memory cells in the adaptive response ensure a faster reaction to previously encountered pathogens. The innate system acts quickly to contain an infection and activates the adaptive system, which then provides a tailored response and long-term immunity.
T cells and B cells play vital roles in the adaptive immune response. Helper T cells activate B cells and cytotoxic T cells, secreting cytokines to stimulate them. Cytotoxic T cells specifically kill infected cells through apoptosis. B cells are responsible for producing antibodies that are highly specific to the pathogen's antigen. When activated by a helper T cell, a B cell differentiates into plasma cells, which secrete antibodies, and memory B cells, which remain in the body for future encounters with the same pathogen. The collaboration between T cells and B cells ensures a specific and efficient response to pathogens, with T cells regulating the response and B cells producing the necessary antibodies.
