MIDTERM STUDY GUIDE

Flashcards covering key concepts from the 'Innate Immune Defenses', 'Hematopoiesis & Roles of Innate Immune Cells', 'Lymphoid Tissue', 'Complement Pathways', 'Cytokines & Chemokines', and 'Adaptive Immunity' sections of the lecture notes.

Innate Immune Defenses

The body's non-specific immunity, present from birth, which prevents infection and colonization.

Physical Defenses (Innate Immunity)

Mechanisms like skin, cells lining digestive tract and airways, mucus, tight junctions, and tears that prevent microbial entry and colonization.

Chemical Defenses (Innate Immunity)

Substances like acid pH, antimicrobial proteins (e.g., lysozymes), and antimicrobial peptides (e.g., defensins) that kill or inhibit microbial growth.

Antimicrobial Proteins

Proteins such as lysozymes that digest bacterial cell walls.

Antimicrobial Peptides

Peptides like defensins that disrupt bacterial and viral membranes.

Complement System

A biological innate immune defense system involved in recognizing and clearing microbial infections.

Biological Defenses (Innate Immunity)

Innate immune cells, such as macrophages and neutrophils, that recognize and clear microbial infections.

Phagocytes

Immune cells (e.g., macrophages, neutrophils) that engulf and destroy pathogens through phagocytosis.

Phagocytosis

A four-step process involving recognition, binding, enclosure, and destruction, allowing phagocytes to destroy extracellular pathogens.

Phagosome

An endosome formed when a phagocyte engulfs a pathogen, removing it from the extracellular space.

Phagolysosome

Formed by the fusion of a phagosome and a lysosome, containing low pH and digestive enzymes to destroy pathogens.

Pathogen Associated Molecular Patterns (PAMPs)

Molecular patterns (e.g., bacterial cell wall components, viral/bacterial nucleic acids) on microbes that are recognized by innate immune cells but are not normally present in the body.

Pattern Recognition Receptors (PRRs)

Receptors on innate immune cells (e.g., macrophages) that recognize PAMPs.

Alpha Macroglobulin

An antimicrobial peptide characterized by a thioester bond.

Toll-like Receptors (TLR)

A type of Pattern Recognition Receptor (PRR) involved in detecting pathogens and initiating immune responses by secreting cytokines.

Cytokines

Secreted proteins that have signaling roles in the immune response.

Hematopoiesis

The process of blood cell development and differentiation.

B cell

An adaptive immune cell that differentiates into plasma cells and produces antibodies.

T cell

An adaptive immune cell that differentiates into cytotoxic T cells (to attack pathogens) or helper T cells (to activate other cells).

Dendritic cell

A phagocytic innate immune cell involved in pathogen destruction and presenting antigens to T cells, kickstarting adaptive immunity.

Eosinophil

A type of white blood cell primarily involved in inflammation and defense against parasites.

Macrophage

A phagocytic innate immune cell that releases cytokines, performs apoptosis, and can differentiate from monocytes.

Mast cell

A white blood cell that releases histamine, contributing to inflammation and allergic responses.

Monocyte

A type of white blood cell that differentiates into macrophages and dendritic cells.

Neutrophil

A phagocytic white blood cell, often the first responder to an infection site.

Plasma cell

A differentiated B cell that produces and secretes large amounts of antibodies to bind and neutralize pathogens and toxins.

Thymocytes

Immature T cells found in the thymus.

Antigen Presenting Cells (APCs)

Immune cells (e.g., dendritic cells, macrophages, B-cells) that process and present antigens to T cells.

Cytotoxic cells

Immune cells capable of directly attacking and destroying infected cells or pathogens (e.g., NK cells, γδ T cells, CTLs, CD8+ T cells).

Granulocytes

White blood cells characterized by granules in their cytoplasm (neutrophils, basophils, eosinophils, mast cells).

Agranulocytes

White blood cells that lack granules in their cytoplasm (lymphocytes and monocytes).

Primary Lymphoid Tissue

Sites where B and T cells develop and mature (i.e., bone marrow for B cells, thymus for T cells).

Bone Marrow

A primary lymphoid tissue where B and T cells are produced, and B cells mature.

Thymus

A primary lymphoid tissue where T cells develop and mature.

Secondary Lymphoid Tissue

Sites where antigen from pathogens and lymphocytes are activated in response to infection (e.g., lymph nodes, spleen, MALT).

Lymph Nodes

Secondary lymphoid tissues that serve as sites for lymphocyte activation, connecting the circulatory and lymphatic systems and containing T cell and B cell regions.

Spleen

A secondary lymphoid tissue that activates T cells and B cells circulating through the blood, also clearing bloodborne pathogens.

White Pulp (Spleen)

The region within the spleen where antigen presentation and lymphocyte activation occur.

MALT (Mucosa Associated Lymphoid Tissue)

Specialized secondary lymphoid tissues found in mucus membranes (digestive, respiratory, urogenital tracts) that gain antigens via M cells.

M cells

Specialized cells in MALT that transport bound materials from the mucosal surface to inside for antigen presentation to lymphocytes.

Peyer's Patch

Specialized MALT located in the mucosa and submucosa layers of the small intestine and ileum, acting as immune sensors and initiating IgA antibody production.

CR3

A receptor for C3b tags on pathogens, facilitating their recognition by phagocytes.

C4bC2b

The classical C3 convertase, an enzyme complex in the classical complement pathway.

C5a

An anaphylatoxin derived from C5 cleavage, which acts as a chemoattractant for immune cells and activates mast cells/basophils.

C3bBb

The alternative C3 convertase, an enzyme complex in the alternative complement pathway.

MBL (Mannose-binding Lectin)

A protein that binds to pathogen surfaces to activate the Lectin Complement Pathway.

C1r/C1s

Proteases that act in the Classical Complement Pathway to cleave C4 and C2.

Factor B

A complement protein that binds to iC3 in the alternative pathway.

Factor D

A C3Pase that cleaves iC3.

Immunoglobulins

Antibodies, which are B cell receptors when expressed on the cell surface or secreted soluble proteins.

C3

A complement protein characterized by a thioester bond, crucial for complement activation.

CRP (C-Reactive Protein)

An acute phase protein that is part of the classical complement pathway.

Cell Lysis (Complement System)

The rupturing of bacterial cell walls by the Membrane Attack Complex (MAC) formed by complement proteins.

MAC (Membrane Attack Complex)

A structure formed by complement proteins that inserts into microbial membranes, leading to cell lysis.

Opsonization (Complement System)

The tagging of pathogens (e.g., by C3a) to activate neutrophils and macrophages for enhanced phagocytosis.

Chemotaxis (Complement System)

The attraction of immune cells (e.g., neutrophils and macrophages by C5a) to the site of infection.

Properdin (Factor P)

An accelerator protein of the complement system.

Factor H

A regulatory protein that acts as a 'brake' on the complement system.

Factor I

A protease that cleaves C3b to form inactive iC3b, regulating the complement system.

DAF (Decay Accelerating Factor)

A protein that inactivates C3bBb and promotes the dissociation of Bb from C3b.

MCP (Membrane Cofactor Protein)

A protein that binds C3bBb, promotes dissociation of Bb, and facilitates cleavage of remaining C3b by Factor I to form inactive iC3b.

Acute Phase Proteins

Proteins produced by the liver (e.g., MBL, C1, CRP, C2) that help kickstart the complement system during acute inflammation.

Chemokines

A type of cytokine that functions as chemoattractants, guiding immune cells to specific locations.

NFκB

A transcription factor activated by extracellular signaling, leading to the transcription of genes for cytokines like IL-1 and TNF-α.

IRF3 & IRF7

Transcription factors activated by intracellular (endosomal or cytoplasmic) signaling, leading to the transcription of interferons and other antiviral genes.

Selectins

Endothelial surface proteins that mediate the initial rolling of leukocytes along blood vessel walls.

ICAM (Intercellular Adhesion Molecule)

An adhesion molecule on endothelial cells that binds to integrins on leukocytes, facilitating firm attachment.

Leukocyte Integrins

Adhesion proteins on leukocytes that bind to ICAMs on endothelial cells, promoting stable adhesion.

Vasodilation

Dilation of blood vessels, increasing blood flow and allowing more immune cells to interact with the endothelium.

Chemokine Gradient

A concentration gradient of chemokines (e.g., CXCL8) that guides leukocytes from blood vessels to the site of infection.

Extravasation

The process by which leukocytes (e.g., neutrophils) leave blood vessels and enter tissues (or bone marrow).

IL-1β (Interleukin-1 beta)

A cytokine that induces fever and promotes the recruitment of white blood cells to the site of infection.

TNF-α (Tumor Necrosis Factor-alpha)

A cytokine that induces selectin expression on endothelial cells, causes vasodilation, and promotes the production of IL-1 and IL-6.

CXCL8

A chemokine that specifically attracts neutrophils and basophils to inflammatory sites.

IL-6 (Interleukin-6)

A cytokine that acts at the hypothalamus to increase body temperature (fever) and activates liver cells to produce acute phase proteins.

IFN-α (Interferon-alpha)

A cytokine that attracts NK cells to the site of infection, an important antiviral response.

IFN-β (Interferon-beta)

A cytokine that stimulates infected and adjacent cells to produce other antiviral proteins and cytokines, boosting antiviral defenses.

Adaptive Immunity

Specific immunity learned after contact with a pathogen, involving B and T cell receptors that can identify specific foreign antigens.

Humoral Immunity

A type of adaptive immunity mediated by antibodies produced by B cells, which can recognize and neutralize pathogens in body fluids.

Cell-mediated Immunity

A type of adaptive immunity where T cells directly target and destroy pathogen-infected cells or support other immune cells.

Immune Memory

A feature of adaptive immunity where specialized daughter B and T cells (memory cells) provide a quicker and more effective response upon re-exposure to the same pathogen.

Cytotoxic T cells (CD8)

A type of T cell that directly attacks and kills pathogen-infected cells.

Helper T cells (CD4)

A type of T cell that activates and supports other immune cells, coordinating immune responses.

Regulatory T cells

A type of T cell that suppresses excessive immune responses to prevent autoimmunity.

LPS (Lipopolysaccharide)

A bacterial cell wall component and a PAMP that can be recognized by both innate and adaptive immune system receptors (e.g., B cells).

T cell Receptors (TCRs)

Transmembrane proteins (heterodimers of α-chain & β-chain) on T cells that bind specifically to peptide antigens presented by MHC molecules.

MHC (Major Histocompatibility Complex) Molecule

Cell surface proteins that present peptide antigens to T cells, indicating the presence of a pathogen to the immune system.

MHC Class I

Presents intracellular peptides (e.g., from viruses) to CD8+ T cells; crucial for defense against viral infections.

MHC Class II

Presents extracellular peptides (from externally acquired proteins degraded in lysosomes) to CD4+ T cells; important for immune responses to extracellular pathogens.

MHC Class III

Refers to a region within the MHC locus that contains genes for immune regulatory proteins and some complementary proteins.

MHC Polymorphism

The high degree of genetic variation in MHC genes (Human Leukocyte Antigen locus - HLA) within a population, leading to different alleles with varying peptide binding specificities.

Human Leukocyte Antigen (HLA) Locus

The human version of the Major Histocompatibility Complex (MHC) locus, characterized by extensive polymorphism.

Fc Receptors

Antibody receptors expressed on various immune cells (e.g., macrophages) that bind to the Fc (constant) region of antibodies, facilitating effector functions.

Isotypes (Immunoglobulins)

Different classes of antibodies (e.g., IgG, IgA, IgM, IgD, IgE), each with distinct constant regions and effector functions.

Neutralization (Antibody function)

The mechanism by which antibodies bind to foreign particles or pathogens, preventing them from interacting with or entering host cells.

Opsonization (Antibody function)

The process where antibodies coat a pathogen, making it more recognizable and easily engulfed by phagocytes.

Complement Activation (Antibody function)

The ability of certain antibody isotypes (e.g., IgM, IgG) to activate the classical pathway of the complement system.

IgE

An antibody isotype primarily involved in allergic reactions and defense against parasites, binding to granulocytes like mast cells.

Antigen Processing

The cellular mechanism by which antigens are broken down into peptide fragments suitable for presentation on MHC molecules.

Clonal Selection/Expansion (B cells)

The process where B cells that recognize a specific pathogen become activated, proliferate (expand), and differentiate into plasma cells and memory B cells.