Immune system (cells and molecules)

(Immunity Overview) What are the two main types of immunity?

Innate and Adaptive immunity.

(Immunity Overview) How are immune responses categorized?

Cellular (immune cells) and Humoral (acellular components in body fluids such as blood and lymph).

(Immunity Overview) When is optimal immunity achieved?

When innate and adaptive responses function in coordination.

(Innate Immunity) What is innate immunity?

The body's inborn, natural first line of defense present from birth.

(Innate Immunity) What is the main goal of innate immunity?

To prevent or respond to infection before pathogens establish an active infection.

(Innate Immunity) What are examples of anatomical and physiological barriers?

Skin, mucous membranes, muco-ciliary clearance, acidic stomach environment, lysozyme in tears and saliva.

(Innate Immunity) What are biological barriers?

Symbiotic microbes that compete with pathogens for nutrients and space, e.g., E. coli producing vitamin K.

(Innate Immunity) What are examples of compromised barriers increasing infection risk?

Burn wounds, loss of goblet cells, ciliary dysfunction in Primary Ciliary Dyskinesia (PCD).

(Innate Immune Cells) What cells are part of the innate immune system?

Mast cells, neutrophils, monocytes, dendritic cells, macrophages, NK cells.

(Innate Immune Cells) What is the origin of all immune cells?

Hematopoietic stem cells in bone marrow.

(Innate Immune Cells) What is meant by non-specific immune response?

Innate cells respond similarly to various pathogens without pathogen-specific recognition.

(Innate Immune Cells) What are the requirements for an effective innate immune system?

Recognition of self vs non-self, mechanisms for destruction, and signaling to adaptive immunity.

(Pathogen Recognition) What are PAMPs?

Pathogen Associated Molecular Patterns—conserved microbial molecules recognized by innate immune cells.

(Pathogen Recognition) What are DAMPs?

Damage Associated Molecular Patterns—molecules released by damaged or dying host cells that trigger immune response.

(Pathogen Recognition) Give examples of PAMPs and DAMPs.

PAMPs: flagella, dsRNA; DAMPs: ATP, uric acid crystals.

(Mechanisms of Threat Clearance) What is phagocytosis?

The engulfment of pathogens into phagosomes that fuse with lysosomes for degradation.

(Mechanisms of Threat Clearance) What is opsonization?

Coating of pathogens by molecules like IgG, C3b, or MBL to facilitate phagocytosis.

(Mechanisms of Threat Clearance) Which cells perform phagocytosis?

Macrophages, neutrophils, and dendritic cells.

(Mechanisms of Threat Clearance) What is apoptosis?

Programmed cell death induced by NK cells or natural cellular processes.

(Mechanisms of Threat Clearance) How do NK cells induce apoptosis?

Through release of perforin and granzymes that create pores and activate cell death pathways.

(Mechanisms of Threat Clearance) What are extracellular traps (NETs, METs)?

Web-like DNA structures released by neutrophils/macrophages to trap and kill pathogens.

(Mechanisms of Threat Clearance) What mechanism do eosinophils use against helminths?

Degranulation—releasing toxic enzymes to kill multicellular parasites.

(Inflammation) What is inflammation?

A biological response to infection, damage, or toxins aimed at protection and healing.

(Inflammation) What are the classic signs of inflammation?

Redness, swelling, heat, pain, and loss of function.

(Inflammation) Which molecules initiate inflammation?

Cytokines, chemokines, and other mediators released by innate immune cells.

(Recruitment and Communication) What is leukocyte recruitment?

Movement of white blood cells from bloodstream to tissues in response to infection.

(Recruitment and Communication) What are the steps of leukocyte recruitment?

Rolling (via selectins), adhesion (via integrins), and transmigration (via PECAM-1).

(Recruitment and Communication) Which cells act as antigen-presenting cells?

Dendritic cells capture microbes and activate T lymphocytes.

(Humoral Innate Components) What are humoral components?

Soluble molecules in body fluids that recognize and neutralize pathogens.

(Humoral Innate Components) What are ficolins?

Pattern-recognition proteins that bind to acetylated sugars on bacteria and fungi.

(Humoral Innate Components) What are defensins?

Small antimicrobial peptides that disrupt microbial membranes.

(Humoral Innate Components) What are interferons?

Proteins produced in response to viruses that inhibit viral replication and activate immune defenses.

(Complement System) What is the complement system?

A group of serum proteins activated in a cascade to eliminate pathogens.

(Complement System) What are the three complement activation pathways?

Classical, Mannose-Binding Lectin (MBL), and Alternative pathways.

(Complement System) What triggers the classical pathway?

Binding of antibodies (IgG or IgM) to the pathogen surface.

(Complement System) What triggers the MBL pathway?

Binding of MBL or ficolins to sugars on pathogen surfaces.

(Complement System) What triggers the alternative pathway?

Spontaneous hydrolysis of C3 and stabilization by factors B, D, and Properdin.

(Complement System) What are the outcomes of complement activation?

Pathogen lysis (via MAC), inflammation (via C3a, C5a), and opsonization (via C3b).

(Complement System) What is the Membrane Attack Complex (MAC)?

A complex (C5b–C9) forming pores in the pathogen membrane leading to lysis.

(Complement System) What are anaphylatoxins?

Small peptides (C3a, C5a) that promote inflammation and attract immune cells.

(Complement System) What is the role of complement in B cell activation?

C3d binding to antigen crosslinks BCR and CR2 on B cells, enhancing activation.

(Complement System) What happens in complement deficiencies?

Impaired clearance of immune complexes, leading to autoimmune diseases like SLE.

(Complement System) How is complement activation regulated?

By inhibitors like C1INH, DAF, MCP, Factor H, HRF, and CD59.