Principles of Immunity and Immunological Techniques in Forensic Science
Module Overview and Learning Objectives
Module Title: Biological Techniques in Forensic Science (FORE20007).
Session Topic: Immunity I: Principles of Immunity.
Institution: Nottingham Trent University (NTU).
Module Learning Objective (MLO1): Discuss the structure and specificity of antibodies.
Session Objectives:
Differentiate between the innate and adaptive immune systems.
Compare the B-cell and T-cell adaptive immune responses.
Understanding Immunity and Its Targets
General Definition of Immunity: The system that defends the body against various biological threats and foreign materials.
Targets of the Immune System:
Pathogens: Examples include bacteria, viruses, fungi, and parasites.
Abnormal Body Cells: Examples include malignant tumors and virus-infected cells.
Toxins: Biological poisons such as Clostridium botulinum.
Foreign Cells: Introduced via medical procedures like blood transfusions or organ transplantations.
Recognition: Each of these targets is recognized by the immune system through distinct mechanisms.
Relevance to Forensic Science
Forensic Application of Immunological Assays: Forensic scientists use these tests to analyze biological materials found at scenes. Key questions addressed include:
Stain Identification: Determining if a stain is blood, saliva, semen, or vaginal secretion.
Species Identification: If the stain is identified, determining if it is of human origin.
Grouping and Typing: Identifying specific classifications, such as blood type (e.g., ).
Individualization: Using the information to link a sample to a specific individual.
Comparison of Immune Systems: Innate vs. Adaptive
Innate Immune System (Non-specific):
Recognition Mechanism: Uses Pattern Recognition Receptors (PRRs) to identify Pathogen-Associated Molecular Patterns (PAMPs).
Components: Physical barriers, inflammation, and phagocytosis.
Speed: Provides an immediate maximal response.
Specificity: Does not require specific antigens.
Memory: Exposure results in no immunologic memory.
Adaptive Immune System (Specific):
Recognition Mechanism: Relies on the interaction between Antibodies and Antigens.
Components: Fluid defense (B-cells) and cell-mediated defense (T-cells).
Speed: Characterized by a lag time between exposure and the maximal response.
Specificity: Highly antigen-dependent.
Memory: Exposure results in long-term immunologic memory.
Classification of White Blood Cells (Leukocytes)
Granulocytes:
Eosinophils
Basophils
Neutrophils
Agranulocytes:
Lymphocytes:
B-cells
T-cells
Monocytes:
Macrophages
Dendritic cells
The Innate Immune System (Non-Specific)
Initial Defenses: Primarily focuses on stopping invasion through physical barriers.
Recognition (PAMPs and PRRs):
Pathogens are recognized by molecular markers on their surface called Pathogen-Associated Molecular Patterns (PAMPs).
Examples of PAMPs include glycans and glycoconjugates.
These are recognized by Pattern Recognition Receptors (PRRs) on immune cells.
The binding of PAMPS to PRRs activates specific signaling pathways.
First Line of Defense: Phagocytosis:
A process of endocytosis where cells engulf and destroy invaders.
Destruction is achieved using (hydrogen peroxide) or lysosomes.
Cells of the Innate System:
Macrophages: Phagocytotic cells that mediate inflammation and release chemicals.
Eosinophils: Phagocytose parasites.
Monocytes: Develop into macrophages.
Dendritic Cells: Phagocytotic cells that mediate inflammation and act as Antigen-Presenting Cells (APCs).
Basophils: Secrete anticlotting factors and histamine.
Natural Killer (NK) Cells: Phagocytotic cells that cause cell death in marked cells.
Mast Cells: Phagocytotic cells that secrete histamine.
Histamine and Physiological Effects:
Causes blood vessels to become leaky (increased permeability of capillaries).
Can lead to allergic responses (e.g., runny nose, sneezing).
Excessive leakage leads to fluid accumulation (swelling), lowered blood pressure, and breathing difficulties (bronchoconstriction).
Associated with frequent heartbeat, adrenaline release, blood clots, and gastric acid secretion.
Second Line of Defense: Inflammation:
A process to destroy or inactivate invaders mediated by chemical communicators.
Steps of Inflammation:
Injury introduces bacteria beneath the skin.
Mast cells secrete histamine to initiate the response.
Capillaries dilate and become leaky.
Fluid and phagocytes exit capillaries into the wound site.
Phagocytes (Neutrophils, Eosinophils, Monocytes, Macrophages, Dendrites) engulf/destroy bacteria.
Capillaries return to normal; the infection is halted.
The Adaptive Immune System (Specific)
Characteristics:
Responds to "non-self" entities (proteins, pollen, toxins, heavy metals).
Remembers previous contact with specific antigens.
Cells Involved:
Lymphocytes: B-cells and T-cells.
Antigen-Presenting Cells (APCs): Macrophages and Dendritic cells.
Stage 1: Recognition:
Lymphocyte membrane receptors bind to specific antigens.
Binding can occur directly on the pathogen or through antigens on circulating APCs.
Stage 2: Lymphocyte Activation:
Binding activates lymphocytes, encouraging cell division with support from T-helper cells.
B-cell Response: Replication of Plasma cells (which release antibodies) and Memory B-cells (which remember the antigen).
T-cell Response: Replication of Memory T-cells and Cytotoxic T-cells (which kill target cells).
Stage 3: Attack:
B-cell Attack: Plasma and B-cells secrete antibodies to recruit more immune cells (e.g., increasing phagocytosis by macrophages).
T-cell Attack: Cytotoxic T-cells attack recognized antigens and release chemicals that trigger apoptosis (programmed cell death).
Questions & Discussion
Question: Is histamine only made within the body?
Contextual Details: The discussion notes that histamine is a critical mediator in the inflammatory response, causing blood vessels to dilate and increasing the permeability of capillaries. It is also linked to the release of adrenaline, frequent heartbeat, and bronchoconstriction.