lecture 11: introduction to the immune system Flashcards
innate immunity
- most plants and animals have some form of innate immunity eg: TLR, complement, lysozyme
- rapid response, but low specificity
- no requirement for MHC, B cell, T cells, but synergises with adaptive immunity in vertebrates
- first line of defence against pathogens
complement system
= a group of proteins that circulate in the blood and when activated, help destroy pathogens through opsonization (marking pathogens for destruction), membrane attack complex formation and inflammation
- made of classical, lectin and alternative pathways
what triggers the different complement pathways
classical –> antibodies on antigens
lectin –> lectin bound to carbs
alternative –> activated spontaneously, by spontaneous
what are C3
central protein involved in all 3 pathways
toll like receptors
- specific type of PRRs
- they recognise conserved microbial structures and transmit signals to the nucleus to alter gene transcription
- sense a variety of microbial molecules
- signal via other adaptor proteins and activate transcription factors
- gene transcription patterns are changed towards pro-inflammatory eg: cytokines are secreted
what does “the immune system is turned on by danger” mean
- triggered by danger not by difference
- microbial invasion to regions rich in leukocytes and TLR (or other PRR) triggers inflammation and immune action
- both commensals and pathogens have PAMPs but commensals generally do not cause extensive inflammation and immune activation
commensals
refer to microorganisms, such as bacteria, fungi, or viruses, that live in or on a host organism (like humans) without causing harm and often provide some benefit to the host
how do innate and adaptive systems respond to commensals and pathogens
- they respond to both commensals and pathogens
- pathogens are intrinsically invasive
- commensals are generally kept out by physical and chemical barriers
- many pathogens act to suppress the immune system
- in the gut, IgA is produced against both commensals and pathogens
adaptive immunity
- slower initial response, but memory response rapid, high specificity
- develops after exposure to a particular pathogen or antigen
- has the ability to remember previous encounters with pathogens
- major histocompatibility complex (MHC) dependent
- requires B cells and/or T cells with somatically rearranged DNA
what are the components of the adaptive immune system and what do they arise from
- bone marrow stem cells generate lineages of white blood cells (leukocytes)
main components:
- monocytes
- lymphocytes
- T cells
- B cells
- Macrophages
- Dendritic cells
myeloid cells: macrophages
- differentiate from monocytes as they migrate into tissues
- major role in phagocytosis
- express MHC-I and MHC-II and act as antigen presenting cells
what do dendritic cells do
- T cell activation
- thymic tolerance
- peripheral tolerance
- T reg induction
dendritic cells
- specialised immune cells that capture, process, and present antigens to T cells, thereby initiating adaptive immune responses
- most potent of all antigen presenting cells (APC)
- mainly found in tissues as ‘sentries’ (eg: skin)
- carry antigen into lymph nodes for surveillance by T cells
- if dendritic cells come into contact with microbes, toll like receptors will be activated
what is the role of CD4 and CD8 T cells
- CD4 “helper” T cells help B cells to make antibody. they also help in the stimulation of CD8 T cell responses
- CD8 T cells can become cytotoxic and kill virus infected or cancer cells
activation of T and B cells process
- dendritic cells activate helper T cells (CD4)
- helper T cells activate CD8 T cells and B cells
- cytotoxic T cells kill virally infected cells
- produces enzymes that can kill cells, result in controlled death = apoptosis - B cells produce antibody that neutralise toxins or ‘tag’ microbes for destruction
