L6 Linking Innate and adaptive immunity

what type of proteins or organic molecules are T cell receptors or Ab (B cell receptors) able to recognise

almost any protein or organic molecule

what will almost any T or B cell that recognises an antigen do

it will become activated and proliferate to create a clonal population, all with the same receptor and so all specific to the same antigen

what is clonal expansion of T and B cells

when a naive T or B cell’s receptor specifically binds its antigen with the correct activation signals, that cell proliferates rapidly to produce many genetically identical daughter cells, all cells in the clone have the same antigen specificity, increasing the strength of the immune response; some become effector cells and others become long-live memory cells

what can happen if T and B cells are activated incorrectly

this can be very dangerous, leads to autoimmunity and allergies

how can innate immune cells recognise pathogens

through pattern-recognition receptors (PRRs), damage-associated molecular patterns (DAMPs) released from damaged host cells, and pathogen-associated molecular patterns (PAMPs) which are conserved pathogen molecules, common to different types of microbes, but differ from the host

What do T cells recognise

8-25 amino acid sequences (peptide)

can a T cell recognise an antigen on its own

no, the antigen has to be presented to it by an antigen presenting cell

what are the only cells that can activate naive T cells

dendritic cells (main activator), macrophages, and B cells

what is the main difference between MHC I and II

MHC I is expressed on all nucleated cells and presents intracellular peptides (such as viral proteins) to CD8+ cytotoxic T cells, enabling killing of infected cells, MHC II is expressed only on professional antigen presenting cells and presents extracellular peptides to CD4+ helper T cells, coordinating immune responses

give an overview of MHC-restricted antigen recognition by T cells

a peptide antigen lies in the binding groove of an MHC molecule on an antigen presenting cell, each MHC molecule can bind a range of different peptides, the T cell receptor binds simultaneously to both the peptide and the MHC molecule, therefore, a T cell can only recognise an antigen when it is presented in combination with self-MHC (MHC restriction)

how long might the peptide sequences in MHC I be

7-11 amino acids

how long might the peptide sequences in MHC II be

13-25 amino acids (longer than MHC I because the peptide sequence can be outside of the groove)