The Human Immune The Human Immune SystemSystem

What defenses do our bodies have against disease?

Immune System Functions

The Immune System helps maintain

homeostatic balance by fighting pathogens and

eliminatingdiseased cells,

recycling dead cells, cell debris, and nutrients.http://www.unitedstreaming.com/index.cfm?media_file_id=1000667

Body Defenses Against DiseaseBody Defenses Against Disease

First line of defense Physical: cilia in respiratory tract, skin Chemical: secretions such as mucus,

tears, and sweat contain lysozyme and other chemicals that fight germs; stomach acid

Specific and nonspecific defenses – immune system reactions

Human Immune SystemHuman Immune System Lymphatic system

– network of vessels that collects, filters, and returns plasma that leaks from the bloodstream.

Organs and cells that filter lymph and blood and destroy foreign microorganisms

Immunity – Resistance to DiseaseImmunity – Resistance to Disease

Passive – comes from outside: Antibodies in breast milk baby Antibodies produced in animal human Immune cell transplant

Active – immune response produced by the body: Antibodies made in response to infection Cells that kill cancer and virus-infected

cells

PassivePassive Immunity Immunity – “Borrowing” – “Borrowing” antibodies from another human beingantibodies from another human being

Ex.: Colostrum is rich in antibodies, comes out before mother’s milk

Passive ImmunityPassive Immunity – “Borrowing” – “Borrowing” antibodies from another human beingantibodies from another human being

Ex.: Gamma Globulin - injected antibodies

Antivenom ProductionAntivenom ProductionEx.: antidote against snake venomEx.: antidote against snake venom

Inject Horse, rabbit, or other animal with venom; animal produces antibodies against

venom.

Milk snake to obtain venom.

Purify antivenom from horse serum.

The antibodies the horse makes are an example of ___________ immunity.

The antibodies injected into a person to treat snake bite are ___________ immunity.

ACTIVE

PASSIVE

Active Immunity – body makes its own antibodies, Permanent Protection

Ex.: Immune reaction after exposure to disease some symptoms

Immune CellsImmune Cells

White blood cells -- leucocytes Made in red bone marrow found in lymph, blood, and tissues Some can migrate to area of infection Fight germs specifically and

nonspecifically

Bone Marrow Stem Cells

Lymph Cells

B-Cells T-Cells

Blood Cells

WBC RBC Platelets

Nonspecific DefensesNonspecific DefensesEffective against many types of pathogens Phagocytes engulf and kill many germs

(macrophages, neutrophils) Natural killer cells kill virus infected cells Interferon – chemical defense against viruses Inflammation – histamines increase blood flow,

immune cells migrate to the area

Neutrophil

Macrophage

Inflamatory Response

Specific ImmunitySpecific Immunity

Effective against a specific pathogen Pathogens have antigens, usually proteins,

that immune cells identify as foreign Body has millions of lymphocytes, special

leucocytes with receptors for specific antigens Lymph nodes – pathogens are identified:

If a lymphocyte is present that has a receptor for the antigen on the pathogen, an immune reaction starts

The presence of the specific receptor depends on having the gene for it.

Lymphocytes & Specific Immune Lymphocytes & Specific Immune ResponsesResponses

T lymphocytes – T cells, mature in the Thymus Helper T cells* – recognize antigens, initiates

immune reaction Cytotoxic T cells – kill cancer and virus infected

cells cell-mediated response B lymphocytes – B cells, mature in the Bone

marrow Make antibodies – proteins that bind to antigens –

when activated by a helper T cell antibody-mediated or humoral response

* HIV infects and kills helper T cells, stopping many immune reactions from happening.

T cells*

B cells*

+

+

Lymphocyte Production & Maturation*

Cell MediatedImmune Response

* Most prevalent with intracellular parasites *

Antigen

digests the pathogen & presents antigens to a helper

T cell

CytokinesEx.: interleukins

APC(Antigen-Presenting Cell, usually a phagocyte )

Cytotoxic T and Killer cellssecrete cytotoxins that kill infected body cells

or CYTOTOXIC T CELL specific for antigen

is activated & replicates

Why? Must destroy infected cells.

Antibody (Humoral) ResponseAntibody (Humoral) Response* most prevalent with extracellular parasites ** most prevalent with extracellular parasites *

1. Helper T cells recognize antigens from pathogens or APC;

2. Helper T cells activate B cells that have the proper antibody shape to start making antibodies;

3. Antibodies bind to pathogens and mark them for destruction by phagocytes or “complement” proteins found in blood.

An Antibody MoleculeAn Antibody Molecule

B cells have antibodies on B cells have antibodies on their surface as receptors their surface as receptors

for activation.for activation.

B cells secrete antibodies B cells secrete antibodies that attach to the antigens that attach to the antigens

on the pathogenon the pathogen

http://www.cellsalive.com/antibody.htm

Antigen-binding sites

OpsonizationOpsonizationAntibodies bind to the antigen on the pathogen’s Antibodies bind to the antigen on the pathogen’s

surface and “tag” the germ for destructionsurface and “tag” the germ for destruction

neutrophils phagocytosing Anthrax bacilli

Complement proteins bind to

antibodies attached to the germ and cause cell lysis

KA-BOOOOM

!!!

B & T Cell Activation & ReplicationB & T Cell Activation & Replication

Helper T

Activated B Cells replicates &secrete antibodies that stick to antigen on pathogen

Activated Cytotoxic T Cells replicate &secrete cytotoxins that kill infected cells

APC

Memory Cells remain after immune Memory Cells remain after immune reaction.reaction.

More prevalent w/ extracellular pathogens

More prevalent w/ intracellular pathogens

Vaccination or Vaccination or ImmunizationImmunization

After a specific immune reaction, memory cells may be left that recognize the pathogen

Vaccination/immunization takes advantage of this: A pathogen (killed or attenuated) or an antigen

from it is introduced into the body An immune reaction against the antigen happens

primary response Memory cells are quickly reactivated when the real

pathogen infects the host in the future secondary response, faster

↓takes

7-10 days

↓Much faster:

1-2 days,Hours?

Disease A

Disease B

What do you infer from the graph?

We react differently to different pathogens/diseases Some reactions are better than othersConsider that:1.The ability to make specific antibodies and cell receptors is genetic.2.We can make 10 million+ different antibodies/receptors by shuffling DNA segments in our genes.3.Making antibodies/immune cells against our own antigens autoimmunity

Allergies (noninfectious)

Immune system produces antibodies to a nonpathogenic substance found in the environment

Plant pollens

Dust

Dust mites

Various foods

Autoimmunity (noninfectious)

Immune system makes antibodies to proteins found in the body, destroying body’s own tissues

Rheumatoid arthritis Rheumatic fever LupusMultiple Sclerosis

BiotechnologyBiotechnology Antibodies are used in many biotech applications; ex.:

immunofluorescence

ELISA assay (Biology Project at U. Arizona)

ImmunofluorescenceAntibodies with fluorescent tags can be used to label different proteins in cells.