Bio 1.8 Immune system

immune system

can be divided into:

• innate

• adaptive immunity

innate immunity

consist of defenses that are always active against pathogens but are not capable of targeting specific invaders

adaptive immunity

long response time but response targets a specific pathogen and maintains immunologic memory of the infection to mount faster response during subsequent infections

B-cell vs T-cell

humoral immunity driven by B-cells and antibodies, cell mediated immunity driven by t-cells

granulocytes

neutrophiles, eosinophils and basophils

agranulocytes

lymphocytes (B and T cells) and macrophages (monocytes)

immune system is found in

• bone marrow [where immune cells come from]

• spleen and lymph nodes are sites where immune response can be mounted and in which the B-cells are activated

• thymus site of T-cell maturation

• Gut associated lymphoid tissue (GALT) includes tonsils and adenoids

leukocytes

white blood cells

non-specific non-cellular defenses [innate immune system]

• skin

• mucus

• tears and saliva [contain lysoszyme]

• stomach

• complement system

• interferons

skin

acts as a physical barrier and secretes antimicrobial compounds like defensins

mucus

traps pathogens; in the respiratory system, the mucus is propelled upwards by cilla and can be swallowed or expelled

tears and saliva

contain lysozyme [an antibacterial compound]

stomach

produces acid, killing most pathogens.

colonization of the gut helps prevent overgrowth by pathogenic bacteria throiugh completion

complement system

punches holes in cell walls of bacteria making them osmotically unstable

interferons

given off by virally infected cells and help prevent viral replication and dispersion to nearby cells

non-specific cellular defenses

• macrophages

• MHC class 1

• MHC class 2

• dendritic cells

• natural killer cells

• granulocytes

• neutrophils

• eosinophils

• basophils

• mast cells

Macrophages

ingest pathogens and present them on major histocompatibility complex.

secrete cytokines (Cytokines signal the immune system to fight infections and injury)

MHC Class 1

presented in nucleated cells and displays endogenous antigen (antigen from within the cell) to cytotoxic t-cells (CD8+ cells)

MHC Class 2

present professional antigen-presenting cells (macrophages, dendritic cells, B-cells and certain activated epithelial cells) and displays exogenous (proteins from outside the cell) to helper T-cells (CD4+ cells)

dendritic cells

antigen presenting cells in the skin

Natural killer cells

attack cells not presenting MHC molecules, including viraly infected cells and cancer cells

Granulocytes

neutrophils, esinophils and basophils

neutrophils

ingest bacteria, opsonisation of bacteria (those that are marked with antibodies)

follow bacteria via chemotaxis

esinophils

used in allergic reactions and invasive parasitic infections.

release histamine causing inflammatory response.

basophils

used in an allergic reaction

circulate in the bloodstream

mast cells

used in an allergic reaction

reside in tissues in the body

adaptive immunity

• humoral immunity

• cell-mediated immunity

humoral immunity

centered on antibody production by plasma cells [which are activated B-cells]

antibodies

target particular antigen

the tip of the variable region is the antigen binding region

when activated antigen binding region undergoes hypermutation to improve the specificity of the antibody produced

circulating antibodies can opsonize pathogens (mark them for destruction), cause agglutination (clumping) into insoluble complexes that are ingested by phagocytes or neutralise pathogens

antibody types

• IgM

• IgD

• IgG

• IgE

• IgA

memory B-cells

wait for second exposure to a pathogen and can then mount a more rapid response (secondary response)

cell-mediated (cytotoxic) immunity

centered on T-cells

t-cells

undergo maturation in the thymus through positive selection (only that can react to antigen presented on MHC) and negative selection (causing apoptosis in self-reactive T-cells)

thymosin is a peptide hormone that promotes T-cell development

helper T-cell (CD4+/ Th)

respond to MHC 2 and coordinate the rest of the immune system

secretes lymphocytes to active various arms of defense

Th1 - secrete interferon to active macrophages

Th2 - activate B-cells in parasitic infections

Cytotoxic T-cell (Tc/ CD8+)

respond to antigen on MHC-1 and kill virally infected cells

suppressor T-cell

tone down response after an infection and promote self tolerance

autoimmune

self-antigen is identified as foreign and immune system attacks the body’s own cells

allergic reactions

non-threatening exposure that incite inflammatory response

immunization

inducing active immunity prior to exposure to a particular pathogen

passive immunity

transfer of antibodies to the individual

lymphatic system

circulatory system that consist of 1 way vessels with intermittent lymph nodes

connects to the cardiovascular system via the thoracic duct

equalises fluid distribution, transport fats and fat soluble compounds in chylomicrons and provides sites for mounting immune responses

hematopoietic cell

immature cells that develop into all types of blood cells, including red blood cells, white blood cells, and platelets. They are also known as blood stem cells.