Immune system Lecturer: Oleg Sergeyev The immune system

Immune system Lecturer: Oleg Sergeyev

The immune system is a system of biological structures and processes within an organism that protects against disease. To function properly, an immune system must detect a wide variety of agents, known as pathogens, and distinguish them from the organism's own healthy tissue. In other words, the immune system works because the body is able to recognize "self" and "non-self."

How the body seeks to defend itself against infection by a variety of pathogens Three defense lines of increasing specificity: Mechanical barriers backed up by biochemical factors Innate immunity Adaptive immunity

The parts of the body that are exposed to or communicate with the external environment Skin sweat, sebaceous gland secretions Mucosal (nose, mouth, urogenital ducts) mucus, ciliary action Stomach acid Urinal urea: flashing action Also: lysozyme in tears and saliva

Symbiotic microorganisms Microorganisms living on the body strongly contribute to its protection. They produce fatty acids, lactic acid helping create conditions unfavorable for most pathogens They secrete bactericins possessing antibiotic-like activity They outcompeting pathogens by sheer number

However, microorganisms do often cross the mechanical barriers and penetrate the body Innate immunity Provides an immediate, but non-specific response Players and factors: Phagocytes Natural killers Complement Interferon

However, microorganisms are able to mutate, produce external factors of pathogenicity (toxins etc.) and thereby overcome the second defense line Adaptive immunity highly specific response, although takes time Often referred to as ‘acquired immunity’ But the whole point is that the immune system adapts its response during an infection to improve its recognition of the pathogen. Activated by the innate response

An EM image of phagocytosis

Phagocytosis scheme

Phagocytic cells Monocytes: mononuclrar cells Compact nucleus Polymorphonuclear cells Multi-lobed nucleus

Toll-like receptors (TLR) TLRs are a type of pattern recognition receptors (PRR) and recognize molecules that are broadly shared by pathogens but distinguishable from host molecules (conserved structures), collectively referred to as athogen-associated molecular patterns (PAMPs). Single, membrane-spanning,noncatalytic receptors usually expressed in sentinel cells such as macrophages and dendritic cells.

Toll-like receptors scheme

Complement system The main humoral component of the innate immune response Represents a biochemical / proteolytic cascade that attacks the surface of foreign cells (i.e. membrane structures)

Differentiation of immunocompetent cells

Antigen presenting cells (APC) Antigen presentation is a process in which some phagocytes move parts of engulfed materials back to the surface of their cells and "present" them to other cells of the immune system. There are two "professional" antigen-presenting cells: macrophages and dendritic cells.

Antigen presentation

Antigen presentation

Antibody-antigen interaction

Antibody-epitope vs receptor - ligand interaction Epitope: 3 – 10 amino acid residues Ligand (domain): 20 or more amino acid residues Molecular patterns (incl. PAMPs) represent domains, not epitopes

Antibody bivalency

Antibody classes

Antibody response back effects

The figure above demonstrates the strong connection of innate and adaptive immunity through antibody response Thank you for your attention