INTRODUCTION TO IMMUNITY

IMMUNOLOGY LECTURE 1

Dr Jayne Powles

By the end of this lecture you should..

• Understand what immunity is • Know the components of & the role of the

immune system• Be able to name each of the WBC, know their

roles & know how to identify them• Know the roles of the lymphoid organs/tissues• Have been introduced to the main forms of

defence the body employs…

• Disease– Damage or injury that impairs normal physiological function.

– Invasion by micro-organism, by parasite, by poison, by cancer, hereditary / genetic cause, by diet, etc.

• Infection– Where micro-organism is established & growing in host

– Doesn’t always cause disease / host damage

Immunity

• If immune to a disease– Does NOT mean cannot contract it– More readily able to fight it as body has been

previously exposed to infection or vaccination

• Unwell – May have contracted a virus, bacteria, etc. that body

is fighting but due to “immunity” - symptoms not severe

Immunity

• Immunity – recognition & removal of non-self (antigen) from self (body)

• Immune system – Fights disease– Consists of organs, cells & molecules

• CELLS – white blood cells, some blood components

• ORGANS – thymus, lymph nodes, spleen, lymphoid tissues

Blood

• Cellular & extra-cellular (plasma)– Plasma

• 90% water• Proteins - albumin, antibodies, fibrinogen, complement

proteins

– Red blood cells (erythrocytes)– White blood cells (leukocytes)-many types– Platelets

Leukocytes (WBC)

Lymphocytes - recognise and respond to foreign antigens– Contain a large round nucleus that stains with hematoxylin.– Source = bone marrow Lymphoid stem cells– Can replicate

Three types:• Natural Killer Cells - innate immunity• T cells – acquired immunity• B cells – produce antibody

Antigen/Antibody Reactions

• Antigen (Ag) = Non-self – eg.microbe, parasite, foreign body, abnormal cell

• Antibody (Ab) = Protein – specifically designed to “fit” onto specific Ags & so

neutralise them

• Ag-Ab complex : – Making Ag ineffective, disrupts Ag surface / functions– Attracting more immunity components to help destroy Ag– Exploited to make vaccinations & antiserums

Specific binding

Monocytes – phagocytic (“eating of microbes”)

• Source = bone marrow Myeloid stem cells• Enter tissues few hours after release into general

circulation• Develop into wandering & fixed macrophages• Long life• Can multiply

Insert picture of monocyte here

Leukocytes (WBC)

Leukocytes (WBC)

• Granular (cytoplasm filled with granules)

Neutrophils • Granules do not take up stain• Enter tissues few hours after release into general circulation• Mature & immature• Life expectancy is few days• Cannot replicate• Phagocytic role

Insert picture of neutrophil here

Leukocytes (WBC)

Eosinophils• Take up acid dyes such as eosin• Circulate blood stream 30 mins than enter tissues• Involved in allergic responses (Type 1 hypersensitivity)• Release molecules that contribute to inflammation

Basophils • Take up basic dyes such as haematoxylin• Generally found in blood stream• Contain vasoactive molecules - makes smooth muscle contract in allergic

responses

Insert picture of eosinophil here

Insert picture of basophil here

Primary Lymphoid Organs

Provide a site for lymphocytes to develop

and mature from a lymphoid stem cell.

Thymus

T lymphocytes develop in the thymus– Thymus degenerates with age as T-cells can divide so

once mature & body has enough, loses its role.

Primary Lymphoid Organs

B cells - develop in different organs depending

on species, eg.• Bone marrow – primates and rodents• Intestinal lymphoid tissues (Peyer’spatches)

- rabbits, ruminants, pigs• Bursa of Fabricius - birds

Secondary Lymphoid Organs Sites where lymphocytes are most active.

Help trap antigens for lyphocytes to act on. Enlarge in response to antigenic stimulation.

Examples:SpleenLymph nodesTonsilsLymphoid tissues (intestinal,

respiratory and urogenital tracts)

Immune System• Body has 2 main ways of defending itself :

– Innate immunity – non-specific, involves barriers, neutrophils & macrophages

– Adaptive immunity – highly specific, involves lymphocytes

• Inflammation– Defence mechanism– Reaction of vascularised living tissue to local injury– White blood cells involved