Cell mediated immunity Flashcards
Two types of adaptive immunity
Humoral
Cell-mediated
Why do we need more than one mechanism of protection
Hugh range of potential pathogens
Susceptible to rapid mutation
May be intracellular or extracellular
How does innate and adaptive system interact
Soluble mediators facilitate antigen uptake by APCs
Cell surface receptors also enhance uptake of antigen
This triggers adaptive response
What is cell ,edited response (CMI)
T lymphocytes eliminate intracellular microbes that survive within phagocytes or other infected cells
What happens to t lymphocyte following presentation by APC
Differentiate into effector cells
Functional types of t cell
Helper (CD4) - TH1 AND TH2 Cells
Cytotoxic (CD8)
Regulatory (CD4 AND CD8 Tregs)
What are naive cells
Mature T cells that have not encountered an antigen
What happens when naive T cell encounters antigen
Proliferation and differentiation into cells capable of contributing to removal of antigen
Where do T cells develop and mature
Thymus gland
Where are T cells produced
Bone marrow
How does the body produce T cells that don’t attack self cells
In the thymus, T cells are exposed to body’s antigens and are destroyed if they react to it
Difference between T cell receptors and antibodies
TCR cannot bind to antigens directly like antibodies can
They need to be presented broken down peptides of antigens by an APC
What are T helper cells
Known as CD4+ cells
Release cytokines increasing activity of other immune cells
How does CMI occur
Th cell activated by APC
triggers rapid cell division and colonials selection of Th cell
Effector Th cell release cytokines that stimulate cells of immune system
matching cytotoxic T cells also recognise the antigen-MHC complex on the APC
Require stimulation from the cytokines to become fully activated
How to cytotoxic T cells destroy infected cells
By releasing toxic granules such as perforin, granzymes and granulysin
How does perforin work
Creates holes in plasma membrane of infected cell
Extracellular fluid flows in
Burstin the cell by cytolysis
Microbes now released into extracellular fluid while they are phagocytosed
How does granulysin work
Flows through perforin channels
Perforated surface of the microbes
Lymphotoxin halts the metabolism of th cell preventing viral replication
How do granzymes work
Release enzymes
These enzymes enter cell via perforin channels
They digest proteins and induce apoptosis
Microbes now released into extracellular fluid where they will be phagocytosed
Function of MHC molecules
To bind peptide fragments derived from pathogens and display them on the cell surface for recognition by appropriate T cells
What does MHC encode for in humans
Human leukocyte antigens (HLAs)
What chromosome is human MHC found in
Chromosome 6
What are class I MHC
Expressed by most nucleated cells
Presents antigen to CD8+
What are class II MHC
Expressed by ‘professional’ APCs - I.e macrophages, Dentretic cells and B cells
Presents antigens to CD4+
What are class III MHC
Products that include secreted proteins that have immune functions like complement system, inflammatory molecules
Why are MHC molecules not very specific
There are up to 6 MHC I and 12 MHC II molecules in an individual
However there are an enormous number of peptides that need to be presented
So they are not very specific to allow this
Promiscuous binding occurs
What is promiscuous binding
A peptide can bind to a number of MHC
an MHC molecule can bind to numerous peptides
How is HLA inherited
Inherited as a set of 3
Inherit one haplotype from each parent, therefore there are four different haplotypes combinations from 2 parents
