Immunology Overview Quiz

Immunology Overview

• The study of the immune system and its functions in protecting organisms from diseases.
• The immune system is a complex network of cells, tissues, and organs that work together to defend against pathogens.

Pathogens

• Any organism with the potential to cause disease.
• Opportunistic pathogens colonize the body without causing disease until the body's defenses are weakened.
• Four types: Bacteria, Viruses, Fungi, and Parasites.

Antigens

• Molecules that stimulate an immune response in the body.
• Antigens are typically proteins, polysaccharides, or lipids found on the surface of pathogens.
• Antigens are unique to a specific pathogen.
• Examples include proteins on cat hairs (triggering asthma), shellfish proteins (triggering allergies), proteins encoded by viruses or mutated genes (in cancer cells).

Immunity Types

• Immunity can be categorized according to its response: innate and adaptive.
• Innate/Natural Immunity: the immediate response to infection, comprising of physical and chemical barriers.
• Adaptive/Acquired Immunity: the long-lasting immunity that develops against one pathogen. This immunity is highly specialized and is of little use against different pathogens.

Innate Immune System – First Line Defenses

• These are the body's immediate defenses.
• Physical barriers like skin, and chemical barriers like sweat, tears, and saliva.
• Epithelial tissue, mucus, and stomach acid are chemical barriers.
• Antimicrobial peptides (defensins) kill pathogens at mucosal surfaces.

Commensal Microorganisms

• These microorganisms enhance animal nutrition by processing digested food and producing vitamins.
• They prevent colonization of disease-causing microorganisms by competing for nutrients and space.
• They secrete antibacterial proteins by killing normal bacteria alongside disease-causing bacteria.

Innate Immune System – Second Line Defenses

• Macrophages are responsible for inducing further defenses in infected tissues.
• They have cell-surface, endosomal, and cytoplasmic receptors to recognize pathogens' unique chemical properties (sugars, fats, proteins, nucleic acids).
• Many different types of receptors, and are not specific for a particular pathogen.
• Destructive effector mechanisms (e.g., phagocytosis) kill and eliminate pathogens.

Inflammation

• Activation of resident macrophages induces inflammation at infection sites.
• Cytokines (e.g., IL-1β, IL-6, IL-12, CXCL8, TNF-α) act as messengers between cells and cause inflammation.
• Inflammation is characterized by heat, pain, redness, and swelling.
• Cytokines induce local blood capillary dilation and increase blood flow (warmth, redness).
• Vascular dilation introduces gaps between cells, increasing permeability, and leaking blood plasma into connective tissue, recruiting neutrophils, monocytes, and natural killer (NK) cells to the infected tissue.
• Inflammatory cytokines are collectively inflammatory cytokines (or pro-inflammatory) cytokines leading to inflammatory states in infected tissues.

Pentraxins

• Inflammatory cytokines change protein synthesis in the liver.
• This increases innate immunity protein production by reducing other protein production.
• Plasma proteins (like pentraxins) bind microorganisms and direct them to phagocytes.
• One example is C-reactive protein.

Complement System

• Complement is a plasma protein system that marks pathogens for destruction.
• Complement coats bacteria and extracellular virus particles, making them easier for phagocytes to engulf.
• Without complement coating, many bacteria resist phagocytosis.

Adaptive Immune Response

• When innate response isn't sufficient to control infection, it calls lymphocytes.
• These lymphocytes (including B & T cells) proliferate and differentiate into effector cells specifically targeting the pathogen.
• The response, which is long-lasting, is adaptive immunity.
• The adaptive innate immunity helps eliminate pathogens.

Lymphocytes

• Recognize pathogens using cell surface receptors, including B and T cells.
• Lymphocytes recognize a pathogen and contribute a powerful response over one to two weeks.
• Lymphocytes move through both blood and lymph.

B-Lymphocytes

• Some activated B cells are converted to plasma cells, which produce antibodies.
• Antibodies travel to the blood, lymph, and infected tissue.
• Antibody number in plasma decreases after a few weeks.
• After infection, some become memory cells, which generate a large number of antibodies with a faster response if the antigen is reintroduced.

T-Lymphocytes

• Effector T cells are cytotoxic T cells, helper T cells, and regulatory T cells.
• Cytotoxic T cells kill infected cells.
• Helper T cells stimulate other cells of the immune system.
• Regulatory T cells control the activities of other T cells to prevent damage.
• Memory T cells provide immunity against reintroduction of the antigen.

Lymphoid Tissues

• The vast majority of lymphocytes are located in specialized tissues called lymphoid tissues or lymphoid organs (bone marrow, thymus, spleen, adenoids, tonsils, appendix, lymph nodes, and Peyer's patches).
• Secondary lymphoid tissues (e.g., lymph nodes) are where mature lymphocytes are stimulated against invading pathogens.
• Lymphoid tissues are functionally divided into primary lymphoid tissues (central), where lymphocytes develop and mature, and secondary lymphoid tissues where mature lymphocytes are stimulated to respond against invading pathogens.

Antigen Receptors of Lymphocytes

• Cell surface receptors on B cells are immunoglobulins.
• On T cells are T-cell receptors (TCRs).
• They recognize and bind antigens.
• Differences in amino acid sequences give these receptors specificities for different pathogens.

Immune System Cells with Various Functions - Additional Notes

• Phagocytes: These cells include neutrophils (most abundant), macrophages (long-lived), dendritic cells (present in tissues and act as messengers to initiate adaptive immunity), mast cells (resident in connective tissues involved in inflammation), monocytes (white blood cells circulating in the blood, mature into macrophages), natural killer (NK) cells.

Notes on Lymphatic System (Diagram Shown)

• The image depicts the lymphatic system's organs and tissues, including lymph nodes, thymus, spleen, bone marrow, and lymphatic vessels, strategically placed throughout the body for immune response coordination.

Summary on Key Concepts

• The immune system is a vital system for fighting off diseases.
• Innate and adaptive responses are important components.
• Each cell and organ plays essential roles for proper response.