2 Immune System Fundamentals and Pathogen Classification

Vocabulary practice flashcards covering pathogen classifications, cellular and chemical components of the immune system, and comparative innate versus adaptive immune mechanisms.

Bacteria

Single-celled prokaryotic organisms lacking a membrane-bound nucleus that possess a peptidoglycan cell wall and are classified by morphology (coccus, bacillus, spirillum) and Gram staining.

Viruses

obligate intracellular parasites, non-living infectious agents that can only replicate inside the living cells of organisms. They consist of a protein coat (capsid) surrounding genetic material, which can be either DNA or RNA, and are typically much smaller than bacteria.

Fungi

Eukaryotic organisms with organized nuclei and cell walls (including yeasts, molds, and hyphae) that are primarily saprophytic but can cause disease by acting as opportunists and releasing proteolytic enzymes.

Protozoans

Unicellular eukaryotic organisms lacking cell walls that act as intracellular and extracellular parasites and disrupt blood and tissue homeostasis.

Multicellular Parasites

Larger eukaryotic metazoan organisms (such as tapeworms, roundworms, and pinworms) that are not microscopic and live within or on host tissues, stealing nutrients and causing structural disruption.

Prions

Infectious, misfolded protein fragments that lack cellular structure and genetic material, which induce damage to central nervous tissue causing fatal neurodegenerative diseases.

Dendritic Cells (Langerhans Cells)

Phagocytic cells located in the epidermis of the skin and mucosal membranes that migrate through lymph vessels to initiate adaptive immune responses.

Mast Cells

immune cells stationed in connective tissue adjacent to blood vessels and mucosal tracts that release chemical granules to mediate localized inflammation and allergic reactions.

Alveolar Macrophages

Organ-resident macrophages fixed within pulmonary alveoli that engulf inhaled dust, bacteria, and pathogens before they penetrate the bloodstream.

Cytokines

small, soluble proteins synthesized by cells of both the innate and adaptive immune systems that regulate overall immune activity.

Autocrine Signaling

Acts on the same cell that released it.

Paracrine Signaling

Acts on neighboring local cells.

Endocrine Signaling

Enters the bloodstream to act on distant target tissues

Interleukins (IL)

A class of cytokines designated numerically (e.g., IL-1, IL-2) that coordinate communication and interactions between leukocytes.

Tumor Necrosis Factor (TNF)

A group of cytokine molecules (such as TNF-alpha and TNF-beta) that mediate systemic inflammatory responses and facilitate target cell destruction.

Colony-Stimulating Factors (CSF)

A class of cytokines, including Granulocyte-CSF, that directs hemopoiesis and leukocyte production within the bone marrow.

Innate Immunity

The genetically predetermined, nonspecific branch of the immune system present at birth that delivers immediate baseline defense against a broad range of foreign substances without immunological memory.

Adaptive Immunity

The acquired branch of the immune system that develops over days following antigen exposure, demonstrating high specificity for molecular targets and establishing long-term immunological memory.

Lysozyme

An antibacterial enzyme present in lachrymal fluid (tears) and saliva that protects mucous barriers by degrading bacterial cell walls.

Histamine

A vasoactive amine released by basophils and mast cells that triggers capillary vasodilation and increases vascular permeability, causing fluid leakage into damaged tissues.

Heparin

An anticoagulant substance released by mast cells and basophils that prevents premature localized blood clotting to facilitate leukocyte access to injured tissue.

Granzymes

Proteolytic enzymes secreted by Natural Killer (NK) cells that pass through perforin membrane pores to activate programmed cell death (apoptosis) in target cells.

Eicosanoids

Specialized membrane-derived lipids that intensify inflammatory signaling.

Complement System

A group of over 30 liver-derived plasma proteins designated by the letter C that circulate in inactive form and activate in cascade pathways to mediate host defense.

Opsonization

The immune process whereby complement proteins coat a pathogen's surface, marking it for rapid identification and binding by phagocytic macrophages.

Membrane Attack Complex (MAC)

A transmembrane pore complex assembled by complement proteins directly in a pathogen's plasma membrane that causes osmotic fluid influx and cytolysis.

opsonization

Complement proteins coat the surface of a pathogen. This "marks" the foreign entity, making it easily recognizable for macrophages to bind and engulf.

cytolysis

Complement proteins assemble directly into the target cell's membrane to form a Membrane Attack Complex (MAC). This structure creates open pores in the pathogen's membrane, inducing rapid influx of fluid, cellular splitting, and cell lysis.

Enhancement of Inflammation

Complement fragments stimulate mast cells and basophils to degranulate and act as potent chemotactic factors that attract neutrophils and macrophages to the injury site.

Elimination of Immune Complex

Complement proteins bind circulating antigen-antibody complexes to erythrocytes (red blood cells). As erythrocytes travel through the liver and spleen, resident macrophages strip off and destroy the antigen-antibody complexes without damaging the red blood cells.