Responding to Antigens

Autoimmune Disease

When an error in the immune system results in the recognition of self-antigens as non-self

Primary pathogens

Cause disease any time they are present

Opportunistic pathogens

Only cause disease when the host’s defenses have been weakened, for example, by poor nutrition or stress

Cellular Pathogens

Have a cellular structure and are living

Non-Cellular Pathogens

Do not have a cellular structure and are non-living

Infection

Occurs when pathogenic bacteria, viruses or other microbes gain entry to the human body and begin to multiply.

Disease

Occurs only after body cells or organs are damaged by the infectious microbes and signs and symptoms of the specific infectious disease are visible.

Incubation period

The interval between exposure to a pathogen and the onset of symptoms

Antigens

• are unique molecules that interact with the immune system

• are found on the surface of the plasma membrane of cells

• act as recognition sites for the immune system

Immunity

the resistance to infectious diseases

White Blood Cells

All immune cells which are derived from multipotent stem cells in bone marrow

Innate Immunity (Non-specific/Natural)

Produces non-specific responses against classes of pathogens, not against specific pathogens

Adaptive Immunity (Specific / Acquired)

Produces specific responses with tailor-made antibodies against each particular microbe

First line of defence

Physical and chemical barriers to prevent pathogens from gaining entry to the body

Second line of defence

Actions of immune cells and soluble proteins mounting a rapid and non-specific attack against pathogens that gain entry

Third line of defence

Actions of immune cells and antibodies tailored specifically to attack each invading pathogen

Physical Barriers

Block or hinder pathogens from entering the organism (intact skin)

Chemical Barriers

Produce chemical substances that make an environment unliveable for a pathogen (Stomach acid)

Microbiological Barrier

Presence of non-pathogenic bacteria (normal flora) which prevent growth of pathogenic bacteria (Presence of bacteria on the skin and in lower gastrointestinal tract)

Phagocytic Cells

eliminate pathogens and cell debris by engulfing them via a process called Phagocytosis

Pattern Recognition Receptors (PRR)

enable cells to identify pathogens by recognising and binding to non-specific molecular patterns found on groups of pathogens

Neutrophils

also release substances such as Cytokines to help fight infection (Cytokines guide other immune cells to site of infection / injury)

Macrophages

found throughout body) and Dendritic cells (found near body surface) also act as antigen-presenting cells (APC’s)

Natural Killer (NK) cells

Large granulated cells which target both abnormal cells (Cancer cells) and virally infected cells

Degranulation

Release of anti-microbial and toxic molecules from membrane-bound granules stored in cytoplasm of some innate immune cells

Mast cells

Stimulated by injury to surrounding cells, antigens or allergens to release histamine (inflammatory response)

Interferons: antiviral agents

Interferons interact with receptors on neighbouring cells causing them to undergo a number of changes that make them less susceptible to viral infection

Complement Proteins

• Become activated when they make direct contact with molecules on the surface of pathogens

• Proteins react with each other, causing a series of reactions known as a Complement Cascade

Fever

Temporary increase in body temperature

The Inflammatory Response

• Inflammation is an early response to infection

• It is normally a short-term (acute) immune response that is localised to site where pathogen has gained entry into the body