3.2.2
Innate and acquired immunity are two essential components of the immune system, which work together to protect the body from pathogens.
Innate Immunity
Definition: Innate immunity is the first line of defense against infections, present from birth. It provides immediate, but non-specific protection.
Key Cells Involved:
Neutrophils: These are the most abundant white blood cells that respond to infections. They engulf and destroy pathogens through phagocytosis.
Macrophages: Larger phagocytic cells that continue the work after neutrophils. They also play a role in alerting the adaptive immune system by presenting antigens to T cells.
Dendritic Cells: These are specialized antigen-presenting cells that capture and process antigens, and then migrate to lymph nodes to activate T cells.
Acquired Immunity
Definition: Acquired immunity is developed over time and provides a specific response to pathogens that have been encountered before, enabling a quicker and more efficient response upon subsequent exposures.
Parts of Acquired Immunity:
Humoral Immunity: Involves the production of antibodies by plasma B cells. These B cells are activated by helper T cells and differentiate to produce specific antibodies that neutralize pathogens.
Cell-mediated Immunity: Primarily involves cytotoxic T cells, which kill infected cells, and is aided by helper T cells, which coordinate the immune response.
Interaction Between Innate and Acquired Immunity
Activation of Acquired Immunity: Innate immune cells, like dendritic cells and macrophages, play a pivotal role in initiating acquired immunity. Once they capture a pathogen, they present its antigens on their surface, activating helper T cells and, subsequently, B cells.
Memory Formation: After an infection, memory B cells are generated, which help in responding faster and more effectively to future encounters with the same pathogen, thanks to the foundational work of the innate immune response in priming T cells and B cells during the initial encounter.
Through this synergistic relationship, the innate immune system provides immediate but nonspecific responses, laying the groundwork for the slower, highly specific actions of the acquired immune system.
B-cells (B lymphocytes) and T-cells (T lymphocytes) both play critical roles in the immune system, although they perform different functions in maintaining health.
B-cells:
B-cells are primarily responsible for humoral immunity, which involves the production of antibodies.
Upon activation by helper T-cells, B-cells differentiate into plasma cells that produce specific antibodies that neutralize pathogens.
They also generate memory B-cells, which enhance the speed and efficiency of future immune responses.
T-cells:
T-cells are mainly involved in cell-mediated immunity.
Cytotoxic T-cells directly kill infected cells and eliminate intracellular pathogens, such as viruses.
Helper T-cells coordinate the immune response, activating B-cells and cytotoxic T-cells, thus playing a pivotal role in bridging innate and acquired immunity.
Immune Response to Infections
Bacterial Infection:
The innate immune system reacts first through neutrophils and macrophages, which phagocytose bacteria.
Dendritic cells capture bacterial antigens and present them to T-cells, activating the adaptive immune response.
B-cells produce antibodies specific to the bacterial antigens, neutralizing them and marking them for destruction.
Viral Infection:
The innate immune response responds similarly, but with a focus on detecting infected cells.
Cytotoxic T-cells recognize and kill virus-infected cells, while B-cells can produce antibodies against the virus.
Helper T-cells activate B-cells and enhance the cytotoxic response of T-cells.
Similarities and Differences
Similarities:
Both responses involve the activation of the innate immune system, which provides the initial defense and alerts the adaptive immune response.
Both B-cells and T-cells participate in the responses after pathogen recognition and play roles in generating memory to protect against future infections.
Differences:
B-cells target extracellular pathogens (such as bacteria) through antibody production, while T-cells are crucial for targeting intracellular pathogens (like viruses) through direct cellular killing.
Response Variability to Pathogens
The body cannot respond in the same way to all pathogens because of the diversity of pathogen types and their mechanisms of infection. Different pathogens exhibit unique structures, life cycles, and methods of evading the immune response, necessitating tailored immune strategies for effective defense.
Types of Pathogens and Infectious Diseases
Viruses: Pathogens that invade host cells and replicate using the host’s cellular machinery, often evading the immune response.
Bacteria: Unicellular organisms that can cause diseases through toxin production or by invading tissues, requiring both humoral and cell-mediated responses.
Fungi: Eukaryotic pathogens that can exploit the host's compromised immune system, often leading to opportunistic infections.
Parasites: Organisms like protozoa and helminths that can complicate the immune response due to their complex life cycles and evasion strategies.
Cellular Components of the Immune System Fighting Disease
Neutrophils and Macrophages: Engage in phagocytosis, removing pathogens and presenting antigens.
Dendritic Cells: Capture antigens and activate T-cells.
B-cells and T-cells: Work in concert to recognize specific antigens and mount an immune response, with B-cells focusing on antibody production and T-cells on direct cellular immunity.
Innate Immunity Defense
Innate immunity provides an immediate, nonspecific response to infections through various cellular components, including physical barriers (skin, mucous membranes), phagocytic cells (neutrophils, macrophages), and inflammation responses.
Acquired Immunity Arises and Defends
Acquired immunity develops over time through exposure to pathogens, leading to a specific and memory-enhanced response. Upon first exposure to a pathogen, the body’s immune system undergoes clonal selection of lymphocytes, resulting in the production of memory cells that enable rapid responses to subsequent infections by the same pathogen.
Prokaryotic and eukaryotic cells differ significantly in terms of their structure and organization:
Main Differences:
Nucleus:
Prokaryotic Cells: Lack a true nucleus; DNA is found in a region called the nucleoid.
Eukaryotic Cells: Have a true nucleus, which encloses their DNA.
Size:
Prokaryotic Cells: Generally smaller in size (usually 0.1-5.0 micrometers).
Eukaryotic Cells: Usually larger (10-100 micrometers).
Cell Structure:
Prokaryotic Cells: Simple structure; do not have membrane-bound organelles.
Eukaryotic Cells: More complex; contain membrane-bound organelles such as mitochondria, endoplasmic reticulum, and Golgi apparatus.
Cell Wall:
Prokaryotic Cells: Most have a rigid cell wall made of peptidoglycan (in bacteria).
Eukaryotic Cells: Some (like plant cells) have a cell wall (made of cellulose in plants), while others (like animal cells) do not.
Reproduction:
Prokaryotic Cells: Asexually reproduce mainly through binary fission.
Eukaryotic Cells: Reproduce both asexually (mitosis) and sexually (meiosis).
DNA Structure:
Prokaryotic Cells: Typically, have a single circular DNA molecule.
Eukaryotic Cells: Have multiple linear DNA molecules organized into chromosomes.
Examples of Cell Types:
Bacterium: Is a prokaryotic cell.
White Blood Cell: Is a eukaryotic cell, which is part of the immune system and helps to defend the
Tears: Provide a physical barrier and contain antimicrobial proteins that help protect against pathogens.
Digestive Enzymes: Present in saliva and other digestive fluids, they help break down pathogens entering through food.
Phagocytes: White blood cells such as macrophages and neutrophils that engulf and destroy pathogens through phagocytosis.
Normal Flora: Beneficial microorganisms that reside in the body and outcompete pathogenic organisms, playing a crucial role in preventing infections.
Secretions: Various fluids produced by the body that contain antimicrobial substances, contributing to the physical and chemical barriers of innate immunity.
Nasal Mucosa and Cilia: Trap and expel pathogens from inhaled air, preventing them from entering the respiratory system.
Cilia: Hair-like structures on epithelial cells that help move mucus and trapped debris out of the airways.
Stomach Acid: Provides a harsh environment for pathogens that are ingested, effectively destroying many potentially harmful bacteria.