Physical and Physical and Chemical Barriers Chemical Barriers to Infectionto Infection

Week 12

Physical BarriersSkinMucus (snot!)

Elaine Chen’s animation

Chemical barriersInterferon (see later)Cytokines

Group of proteins secreted by immune cells to recruit and activate other immune cells (activates either humoral or cellular response)

Complement proteins (see later)

Lymphatic systemLymphatic system

Distribution of lymphoid organs and tissues which make up the immune system

Lymph nodes

Lymphatic systemLymphatic system

Blood cellsBlood cells

Human blood showing different kinds of blood cells.

Various white blood cells (phagocytes) have densely staining nuclei.

White blood cellsWhite blood cells

White blood cells White blood cells (phagocytes)(phagocytes)

Neutrophil cells that have ingested bacteria.

The bacteria appear as the smaller purple rod shapes inside the cells

Radioactively labelled macrophages and a few lymphocytes

Non-specific vs. Specific Non-specific vs. Specific responsesresponses

Non-specific responseNon-specific response

Pathogen Invades Tissue

Non-specific defences

Specific defences(see next section)

Barriers to entry

Physiological

mechanisms

Fever

Chemical mechanis

msComplement proteinsInterferon

Phagocytes and natural killer (NK) cells

Inflammation

BasophilsMast cells

andPlatelets

Histamine, Phagocytos

is

First line of defenceFirst line of defence

Chemicals on the body surface also inhibit infective organisms

The first line of defence against infection is the body surface which acts as a barrier (physical/chemical

barriers – already discussed)

Second line of defenceSecond line of defence Includes:

Fever Interferon/Cytokines Complement proteins Phagocytes (white blood cells) Natural killer (NK) cells Inflammation Blood clotting

FeverFeverFever

Interferon/ CytokinesInterferon/ Cytokines Interferon/

cytokines

Complement proteinsComplement proteins

Complement proteins lyse many bacterial species.

This attracts phagocytes to the site of infection.

Bacteria which have been coated by other complement proteins are readily ingested by the phagocytes.

Complement proteins

Complement proteinsComplement proteins

PhagocytosisPhagocytosis

Stages of phagocytosis: a neutrophil ingesting a bacterium

Macrophage animation

Natural Killer (NK) cells

3 animations

InflammationInflammation

a) Injury to an otherwise healthy skinb) Vasodilation and increased permeabilityc) Phagocyte migration from capillaries to cut aread) Phagocytosis of bacteria and other debris by

macrophages

Inflammation occurs if bacteria enter a cut

InflammationInflammation

Pathogens enter tissues

Mast cells

Basophils

Platelets

Produce Histamine and other

substances

Blood vessels dilate

Increased blood flow

to the region

Capillaries

become permeab

le and leaky

Complement proteins

attract phagocytes

Phagocytes move to the area

Redness

Heat

Edema

Pus

Increased Phagocyt

es

Blood ClottingBlood Clotting

Red blood cells trapped in

protein fibres

Some steps involved in blood clotting and wound healing