Intro to the Immune System

innate immune system

host defense mechanisms that do not adapt to a particular pathogen or generate immunity

adaptive immunity

antigen specific immune responses generated by B and T lymphocytes and includes immune memory

immune memory

the ability of the immune system to respond more rapidly and effectively

recognizing absence of self

missing self molecules like MHC I

pattern recognition receptors

membrane bound and soluble receptors that recognize non-self and are part of innate immunity

BCR and TCR

somatic generated receptors part of the adaptive immunity

ligand

a molecule that forms a complex with another molecule or receptor

affinity

strength of interaction; single binding site

avidity

total strength of binding at multiple sites

antigen

a ligand that elicits an immune response

epitope

the smallest identifiable part of an antigen bound by a receptor

immunogen

an epitope that induces an immune response

hapten

a molecule that does not induce an immune response unless bound to an immunogen

toleragen

a molecule that induces adaptive immune unresponsiveness to train the immune system

factors that affect immunogenicity

size, complexity, conformation, chemical properties

physical barriers

skin, mucous membranes, hair, cilia, urination

chemical barriers

pH, antimicrobial molecules

antimicrobial molecules

defensins, fatty acids, RNAse, DNAse, lysozymes

biological barriers

commensal microbes that compete for resources, produce antimicrobial peptides, and train the immune system

pattern recognition receptor (PRR)

a preformed receptor in the innate immune system that recognizes broad motifs found in pathogens

pathogen associated molecular patterns (PAMPs)

sugars, proteins, lipids, and nucleic acids

Toll-like receptors (TLRs)

type of PRR that detect specific pathogen associated molecular patterns and trigger a signaling pathway

killer activation receptors

preformed receptors that detect MICA and MICB and kill cells

killer inhibition receptors

preformed receptors that detect MHC I and can save the cell

complement receptors

preformed receptors on phagocytic cells that facilitate binding, ingestion, and internal degradation of tagged microbes

Fc receptors

preformed receptors that bind a specific epitope that has gone through a conformational change

IgE

an antibody that can be bound by specific cells in the absence of an epitope

somatically generated receptors

receptors that are randomly generated by chromosomal rearrangements

B-Cell receptors

somatically generated receptors with cell surface immunoglobulin that signal through Ig alpha and Ig beta to activate a call

can differentiate into plasma cells

T-Cell receptors

somatically generated receptors with cell surface receptors and a heterodimer that are associated with CD3 complex

CD4 and CD8 act as receptors

thymus

the first lymphoid organ to develop that is the site for education of T-cells

positive selection

determines if a T cell can tell self from non-self

negative selection

determines if a T cell will react to a self peptide

bone marrow

a primary lymphoid organ that is the site of development of B cells

spleen

an organ that filters blood and concentrates blood borne antigens and microbes

has a high concentration of macrophages that can destroy encapsulated bacteria

lymph nodes

structures that filter lymph fluid and are sites for mixing of dendritic cells, monocytes, and lymphocytes

mucosal-associated lymphoid tissue

sites other than lymph nodes where lymphocytes and antigen presenting cells mix

lymphatic circulatory system

additional circulatory system outside of the cardiovascular system that carries WBCs, cell debris, and lymph fluid

pluripotent hematopoietic stem cells

precursors to leukocytes

leukocytes

cells that defend against microbes, are classified by morphology, and have specialized roles in the immune response

myeloid lineage

the cells that make up the innate part of the immune system

monocytes

agranular leukocytes that are in the circulation and perform phagocytosis

macrophages

agranular leukocytes that reside in the tissue, perform phagocytosis, and are pro antigen presenting cells

dendritic cells

agranular leukocytes that are found throughout the body, perform phagocytosis and macropinocytosis, and are pro antigen presenting cells

neutrophils

granular leukocytes that release granules containing antimicrobial factors (killing themselves in the process) and produce neutrophil extracellular traps

basophils

granular leukocytes that have histamine, leukotrienes, proteases, and pro-inflammatory cytokines; found in circulation

mast cells

granular leukocytes that contain histamine, leukotrienes, proteases, and pro-inflammatory cytokines that are tissue specific

eosinophils

granular leukocytes that are important in helminth responses and contain proteins that are pro-inflammatory and toxic

B cells

lymphoid cells that are specific and produce only one type of antibody for one epitope

plasma cells

terminally differentiated B cells that act as antibody factories

T cells

lymphoid cells that have two main types: CD4+ and CD8+

CD4+ T cells

T cells that recognize MHC II; also called T helper cells

CD8+ T cells

T cells that recognize MHC I and kill cells infected with intracellular bacteria and viruses; also called cytotoxic T cells

NK Cells

cells that lack CD3, TCR, and BCR that kill virally infected cells and tumor cells

express KARs and KIRs

contain perforin and granzyme

NKT cells

express TCR and respond to lipids, glycolipids, and hydrophobic peptides

complex proteins

the type of molecule that elicits the highest response

defensins

molecules that damage microbial cell walls

MICA/MICB

ligands that activate NK cells

lymphoid lineage

contains cells that are part of the adaptive response and cells that are part of both the innate and adaptive response

myeloperoxidase

an antimicrobial factor in the granules released by granulocytes