Immunity 2, Introduction and Classification, Take 2

Two types of immunity

The body is protected against microorganisms in basically two ways. The first is by innate immunity which is also referred to as non-specific. These non-specific mechanisms act against a wide range of potential infectious agents in a non- discriminating way. Secondly, immunity may be acquired, also called specific or adaptive immunity. In this form of immunity the body learns how to combat a particular species of microorganismImmunity

Infectious disease

Koch`s Postulates

1. The specific causative agent must be found in every case of the disease.

2. The disease organism must be isolated in pure culture.

3. Inoculation of a sample of the culture into a healthy subject must produce the same disease.

4. The disease organism must be recovered from the inoculated subject.

Immunity

Innate (non-specific)

Normal A and P

Inflammation

Phagocytosis

Complement

Interferons

Natural killer lymphocytes

Acquired (specific)

Active

Infection

Vaccination

Passive

Transplacental

Colostrum and milk

Injections

Active on passive

Innate immunity

Phagocytosis

Phagosome

Lysosome, lysozyme

Phagolysosome

Phagocytes

Neutrophils

Monocytes

Macrophages

Complement

Antimicrobial substances

30 plasma proteins in inactive form

Immune and inflammatory functions

Activated by microbial polysaccharides or antigen antibody complexes

Complement cascade

Functions of complement

Enhances ‘complements’ inflammation

Attracts phagocytes

Opsonins, opsonisation, phagocytosis

Membrane attack complex, cytolysis

Interferons

Produced by some virus infected body cells and leucocytes

Act against a wide range of virus infections

Viral reproduction is inside cells

Virus infected cell secretes interferon

Interferon bind to interferon receptors in adjacent cells

Functions of interferons

Stimulated cells produce antiviral enzymes to reduce intracellular viral replication.

Cellular ability to produce new proteins is inhibited

Fire brake is therefore produced

Activation of neutrophils and macrophages

Some anti-tumour and anti-metastasis functions

Natural killer cells

Lymph nodes spleen, bone marrow, blood

Secrete a cytokine called perforin

Can kill microbes, tumour cells, virus infected cells

Produce interferon

Stimulate apoptosis

Acquired (specific)

Adaptive with memory

Antigens stimulate synthesis of antibodies

(Antibody generating molecules)

Immune cells

Linking innate and specific immunity

Antigens enter the body

Antigen is detected by antigen presenting cells, (macrophages, dendritic cells and B lymphocytes)

Macrophages release cytokines that stimulate the bone marrow and act on hypothalamus

Activated APC migrate into the afferent lymph vessels

Antigen migrates into the afferent lymph vessels

Antigen is detected by APC and B lymphocytes in the lymph nodes

Antigen attaches to B cell surface receptors

Antigen is also presented to B cells

Antigen/MHC complex is presented to T cells by APC

Activated B and T cells undergo clonal expansion

Both B and T cells differentiate into effecter and memory cells

Plasma cells secrete antibodies

Antibodies kill infecting antigens

Antigen processing and presentation

T cells respond to protein antigen, but not in naive form

Needs component polypeptides bound to cell surface MHC, same as HLA (human leucocyte antigen)

Peptide / HLA complex is recognised by T cells

APCs can be any cell, but mostly dendritic cells, macrophages and B lymphocytes

Antigen presentation takes place in lymphatic tissue, lymph nodes and spleen

B cells can recognise unprocessed antigen but respond better to presented antigen

Cellular immunity

Active against;

Intracellular pathogens

Fungi

Cancer cells

Transplanted tissue

Cells attacking cells

Involves;

T cytotoxic

T helper

Activities;

T helper and suppressor cells have a coordination role

T helpers stimulate (help) B cell clonal expansion

Cytotoxic T cells kill infected body cells and cancer cells

Antibody mediated (humoral) immunity

Active against;

Extracellular pathogens, mostly bacteria

Antigens dissolved in body fluids, bacterial toxins, viruses

Involves;

B lymphocytes

Plasma cells, secrete antibodies

B memory cells

Activities;

Antigen – B cell interactions mostly occur in lymph nodes

Later cells have greater affinity for the antigen than the original B cell

Memory cells live in the lymph nodes

Immunoglobulins

Soluble proteins

Gamma globulins, immunoglobulins, (Ig).

20% of plasma protein

In serum after activation of B cells by antigen

High affinity in later responses

Placental migration

Agglutination of pathogens.

Precipitation of soluble antigen.

Neutralise toxins, covering toxic sites.

Act as opsonins.

Antibody dependent cytotoxicity.

Immune complexes activate complement.

Primary and secondary response

Immunological memory

Subsequent exposure reduces lag time

Secondary response does not need T cell stimulation