Immune System Basics

IMMUNE SYSTEM BASICS

HOW A VIRUS ATTACKS THE BODY.HTTP://WWW.YOUTUBE.COM/WATCH?V=RPJ0EMEGSHQ&FEATURE=RELATED

PATHOGENS Any biological agent that causes illness

and/or disease to its host. Also known as a germs, simple as that!

Different types of pathogens include the following:

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Pathogens will trigger the immune system to respond.

3 MAIN DEFENSES

External Barriers

Non-specific Internal (aka INNATE)

Fever & Inflammatory response

Immune Response

EXTERNAL DEFENSE Skin produces

Sweat which contains lysozymes

Oil – traps bacteria / fungi

Mucus membranes of digestive and respiratory tract produceMucus to trap foreign particlesCilia sweep the mucus to be

cleared from body

NON-SPECIFIC INTERNAL DEFENSEWHITE blood cells

Monocytes and Neutrophils are able to cross capillary walls

use PHAGOCYTOSIS to engulf foreign invaders

Natural Killer cellsRespond to chemical message from Neutrophils; sensing molecular changes in cells causes the release of cytotoxic proteins into “foreign cell”.

NON-SPECIFIC INTERNAL DEFENSE Inflammatory Response

Histamines make capillary walls “leaky”

RBC, WBC, platelets and fluid cross capillary walls

swelling, redness and warmth in the injured area

PUS formation – tissue debris, microbes and WBC (dead and alive)

NON-SPECIFIC INTERNAL DEFENSE FEVER – triggered if pathogen is in

bloodstream or infection is now systemic rather than localized.

102 – 1030 F is beneficial high temp in fighting viral infections and triggers release of interferon.

Interferon literally interferes with viral replication.

SPECIFIC INTERNAL RESPONSE aka IMMUNE RESPONSE Use Lymphocytes

B-Cells = humoral T-Cells = cell mediated

Thymus, lymph nodes and spleen house these cells until called into action by interleukins and cytokines.

Leukocytes (White Blood Cells)

lymphocytes

T cells B Cells NK Cells

WHITE BLOOD CELLS

B CELLS B Plasma Cells- when the B

cell produces the antibody for a specific antigen, it begins to clone itself into B plasma cells, that produce more of that particular binding antibody.

These cells release immunoglobulin, or antibodies.

B plasma cells have a 5 to 7 day life-span; all its protein synthesis energy is going into the production of Antibodies, not self preservation.

B Memory Cells- These are the same as B plasma cells, except they remain inactive until the secondary immune response

Secondary immune response is considered anytime the body encounters a pathogen after the first time. Quicker response time.

Primary response is the first time the body encounters a specific pathogen, Lag period before B cells respond.

T CELLST cells

Helper T cell (Th)

Memory T cell

Helper T cell

Killer T cell

Suppressor T cell

Killer T cell (Tk)

Suppressor T cells - in charge of slowing and stopping the immune response after the foreign substance is destroyed.

Helper T cells - secrete lymphokines that direct B cells into producing antibodies and also direct the Killer T cells as to which cell they get to eliminate.

Killer T cells - They find specifically coded infected cells, and then destroy them with cytotoxins. They may be directed by Helper T cells

Memory T cells - derived from Helper T cells, have the same properties as their parent cell, and circulates until the body encounters the pathogen its parent cells were designer for.

ANTIBODIES & ANTIGENS

Antigens= a fragment of a protein or peptide from the pathogen, taken to the surface of the infected cell and bound in an MHC (major histocompatibility complex) molecule.

The class 1 MHC complex molecule and the foreign peptide form the antigen, which can be read by the receptors on Killer T cells.

CellClass 1 MHC molecule

Antigen

Pathogen

Antibodies are produced by B cells, when stimulated by lymphokines from helper T cells. The antibody attaches to the antigen, completing the signal, coding the infected cells for destruction.

Antibodies are constructed of DNA fragments, making them so unique and almost innumerable.

ANTIBODIES – PROTEINS CREATED BY B-CELLS THAT “LOCK” DOWN FOREIGN ANTIGENS

Antibodies are shaped to match antigen binding sites called epitopes.

Epitopes are the accessible portion of the antigen – a single bacterial surface protein can have several different epitopes.

B-CELL RECEPTORS

“Y” shaped proteins extend from cell membrane.

2 heavy chains 2 light chains that

can be rearranged to match antigen.

T-CELL RECEPTORS

2 parallel protein chainsa - chainb – chainThese chains form the recognition site for each different antigen.

HOW ANTIGEN RECOGNITION BY LYMPHOCYTES WORKS

MHC – major histocompatibility complex Chemical signaling proteins

Class I MHC – found on ALL cells to tell self from non-self

Class II MHC – found on macrophages & B-cells display antigens to Helper T-cells

APC – antigen presenting complex Chemical signaling displays antigen

CELL MEDIATED IMMUNITY

Helper T-Cells respond to chemical signals presented by macrophage.

Helper T-Cells stimulate cytokines and interleukin which triggers production of B-cells and cytotoxic T-cells.

Helper T cells function in both Humoral & Cell Mediated immunity.

Cell mediated =T-Cell

CELL MEDIATED IMMUNITY

T-cells attack invaders directlyPerforins released by cytoxic T-Cells

create pores in infected cell resulting in ion/water inflow cell lysis

Effective against intracellular parasites

Infected cell

PerforinsT-Cell

T-CELLS INTERACTION WITH ANTIGEN PRESENTING CELLS

In both interactions the MHC receptor allows a T-cell to bind which starts defense response.

In (a) an infected body cell alerts cytotoxic cells to destroy infected cell (short term).

In (b) a macrophage displays antigen which triggers immune response (long term).

The ability to resist a pathogen Two forms of immunity;

◦ ACTIVE – direct exposure that creates immune response.

◦ PASSIVE – induced exposure through vaccination.

WHAT IS IMMUNITY?

IMMUNITY INVOLVES PRODUCING A PRIMARY IMMUNE RESPONSE Step one – virus or bacteria infects body cell Step two – macrophage recognizes foreign

antigen of pathogen and engulfs it presenting antigen to alert SPECIFIC DEFENSE SYSTEM

Step three – macrophage activates Helper T-cells Helper T-cells set up the two prong attack of the

immune response

DEVELOPMENT OF PRIMARY IMMUNE RESPONSE - CONTINUED

Step four –Helper T-cells activate both plasma B-cells and Cytotoxic T-cells

Step five - B-cells form plasma cells which make antibodies to match foreign antigens of pathogen

DEVELOPMENT OF PRIMARY IMMUNE RESPONSE - CONTINUED

antibodies

Step five part 2- memory B-cells are created to always remember foreign antigen.

Step six – Antibodies made by plasma B-cells

find & attach to pathogens antigens

DEVELOPMENT OF PRIMARY IMMUNE RESPONSE - CONTINUED

Step seven - Antibodies mark pathogens for destruction.

Step eight - Cytotoxic T-cells locate and destroy infected cell by making a hole in the cell membrane.

DEVELOPMENT OF PRIMARY IMMUNE RESPONSE - CONTINUED

IMMUNE RESPONSE 2-PRONG ATTACK TRIGGERED WHEN HELPER T-CELLS ARE ALERTED

5b. Creation of Memory B-cell

IMMUNOLOGICAL MEMORY The reason why vaccines make sense, and we

eventually build a tolerance to certain diseases…

It’s because after every encounter with a pathogen, both the T cells and the B cells differentiate into an inactive form of their parent cell. They remain inactive until the second immune response for that specific pathogen.

Vaccination is an introduction of a dormant or dead pathogen, which allows our body to do its primary immune response without the risk of actual sickness.

HOW DO VACCINES WORK? Vaccine contains a dead

or weakened pathogen or protein from pathogen.

Most vaccines are only effective against infections before you get them.

Vaccines can wear off overtime booster shots revive immunity.

IMMUNOLOGICAL MEMORY

Heightened secondary response is due to long lived memory cells as a result of first exposure to antigen A.

IMMUNE RESPONSE 2-PRONG ATTACK TRIGGERED WHEN HELPER T-CELLS ARE ALERTED