Pathogens + Innate Immune System

Immunity

contrast self and non-self antigens

• Self antigens are antigens that are recognised by the immune system as belonging to the organism, presenting the organism's own protein.

• Whereas non-self antigens are identified by the immune system as non-self, presenting proteins that aren’t the organism's own.

compare and contrast two types of MHC molecules

• Both MHC I and II are antigens that are expressed on a cell’s membrane.

• While all nucleated cells express MHC I proteins, only antigen presenting cells express MHC II markers.

• MHC I proteins express antigens produced by the cell, whereas MHC II proteins express antigens processed from engulfed substances.

compare pathogen to antigen to allergen

• A pathogen is an organism/agent that can cause an infectious disease.

• An antigen is a substance that triggers an immune response.

• An allergen is a non-pathogenic innocuous substance that is recognised by the immune system as a pathogen, triggering an immune response known as an allergic reaction.

Pathogen, define

A pathogen is an organism/agent that can cause an infectious disease.

Antigen, define

An antigen is a substance that triggers an immune response.

Allergen, define

An allergen is a non-pathogenic innocuous substance that is recognised by the immune system as a pathogen, triggering an immune response known as an allergic reaction.

explain the properties of viruses, including how they replicate

• A virus is a non-cellular pathogen, that is entirely reliant on the host cell's resources.

• It is composed of a capsid surrounding a RNA or DNA core.

• It injects its genetic material into a host cell to replicate.

How do bacteria harm cells

They release toxins

Prions

Abnormally folded proteins that induce the equivalent conformational shape change on normal variants of the same protein.

example of a disease caused by:

• Virus→Covid-19

• Prion→Mad cow disease

• Bacteria→E. Coli

• Fungi→Ringworm

• Protists→Plasmodium (malaria)

• Endoparasite→Tapeworm

• Ectoparasite→Lice

What is the purpose of a fever

To increase temperature to kill pathogens and increase enzymatic activity.

Physical barrier - Humans

Intact skin, Cilia, Mucus secretion

physical barrier preventing pathogen entry.

Chemical barrier

Lysozymes in tears and saliva, stomach acid, acidic sweat,
causes lysis of bacteria.

Microbiological barrier

Normal gut microflora/microbiota; outcompete pathogens, minimizing nutrient, mineral and space availability;

lives in mutualistic symbiosis with humans.

Physical Barriers - Plants

• Thick bark: impermeable water proof layer, prevents entry of microorganisms

• Waxy cuticle: impermeable water proof layer, prevents entry of microorganisms

Chemical Barriers - Plants

• Defensins: peptides toxic to microbes and fungi

• Saponins: disrupts fungi cell wall

• Caffeine

• Tannis

Function of Macrophages/dendritic cells

Macrophages engulf (phagocytose) pathogens which are then broken down by lysozymes in the lysosome, and then presenting their antigen (degraded protein) on its MHC II markers. Macrophages then travel to the lymph nodes for use by the adaptive immune system.

Function of Neutrophils

Neutrophils phagocytose pathogens & cell debris. Secrete cytokines. Undergo apoptosis (self-destruct) following phagocytosis.

Function Of Mast Cells

Detect cells presenting non-self antigens, they degranulate, releasing histamine, causing blood vessels to dilate and become leaky.

Function of Eosinophils

Eosinophils are large, granulocytes that target pathogens which are too large to be phagocytosed, such as parasites; When they come into contact with the pathogen, they degranulate, releasing chemical mediators stored in their vesicles to destroy the pathogen.

Natural Killer Cells

Natural Killer Cells are large, granulocytes that target virally infected and abnormal cells, they attack and destroy cells which have downregulated MHC class 1 markers.

3 Functions of Complement Proteins

• Opsonisation

• Chemotaxis

• Lysis of pathogens

Opsonisation

binding onto the membrane of pathogens marking them as foreign, making it easier for immune cells to recognize them.

Chemotaxis

a chemoattractant gathers near the pathogen, attracting phagocytes to the pathogen increasing its likelihood of being destroyed.

What is complement protein lysis

Complement proteins form a membrane attack complex on the pathogen, which creates pores in the membrane, causing lysis of the pathogen, destroying it.

explain inflammation

• Inflammation is initiated when damaged cells release cytokines to activate nearby mast cells to release histamine.

• Histamine binds to blood vessels causing vasodilation which increases blood flow and increased permeability that makes the blood vessels more leaky.

• This makes phagocytes able to easily leave the blood vessels and there is an increase in fluid leaving blood vessels to the area of inflammation.

explain the following cytokines: Chemokines

induce chemotaxis, attracting immune cells to the site of infection.

explain the following cytokines: Interleukin

Chemical messengers that promote the differentiation of lymphoid stem cells.

explain the following cytokines: Interferon

Chemical messengers that are secreted by virus-infected cells to non-infected cells; activates anti-viral genes which inhibits the synthesis of viral proteins within the cell and attracts natural killer cells.

compare and contrast the first line of defense to the second line of defense

• Both the first and second line of defence are innate, meaning that they are non-specific, targeting all pathogens with the same approach.

• The first line of defence is the chemical, physical and microbiological barriers that prevent pathogens from entering the organism, whereas the second line of defence is the intracellular immune response, which is not dependent on the specific pathogen.

explain the steps of phagocytosis

• Phagocytes phagocytose the pathogen, trapping it inside a vesicle.

• Lysosomes containing lysozyme fuse with the vesicle breaking down the pathogen.

• If the cell is an antigen presenting cell, fragments of the pathogen are then presented on MHC II markers for presentation to the adaptive immune system. If not, then the cell will undergo apoptosis.