Flashcards in Major histocompatibility complex Deck (31)
what is needed for an appropriate response to a foreign antigen?
lymphocytes must recognise antigens to be stimulated to divide and differentiate
what does each lymphocyte have?
its own antigen specificity
what initates a primary response?
recognition and binding to an antigen by a specific lymphocyte
What does the primary response produce?
-Effector cells- job to eliminate antigen
-memory cell pool
Describe the role of the memory cell pool.
-Long lived and still specifc to antigen
-Gone through one round of activation so during second encounter to the same antigen there is a faster and greater response which produces more effector cells and a larger memory cell pool
what is antigen recognition on B cells mediated by?
what is antigen recognition on T cells mediated by?
T cell receptor (TCR)
what do T cells only recognise?
antigens that are expressed on cell surfaces
where can antigens expressed on cell surfaces be derived from?
-These antigens can be derived from pathogens that replicate within host cells e.g. viruses or intracellular bacteria
-Alternatively these antigens may come from pathogens or their products that have been endocytosed from the extracellular fluid
In both T and B cell cases, what do cells display on their surface?
peptide fragments derived from the pathogen's proteins
what can be detected by T cells?
presence of infected cells and foreign antigens
what is major histocompatibilty complex (MHC) ?
Specialised glycoprotein that delivers pathogen-derived peptides and presents them at the cell surface
where are MHC proteins encoded for?
large cluster of genes on chromosome 6
what happens when MHC antigens on transplanted tissue are recognised by recipient's immune system?
what are MHC molecules also refereed to as?
HLA- human leucocyte antigens
what does T cells recognise ?
combination of MHC molecule and small peptide fragment of antigen
what are the 2 MHC families?
what are the 3 members of Class I?
HLA-A, HLA-B and HLA-C
what are the 3 members of Class II?
HLA-DP, HLA-DQ and HLA-DR
what makes each class distinct?
distinct subunit compositions but similar three-dimensional structures
where is class I expressed?
expressed on all nucleated cells including leucocytes
where is class II expressed?
expressed only on leucocytes which present antigen to T cells e.g. monocytes, marcophages
what does each individual express?
two forms of each protein co-dominantly - one derived
from the mother, one from father
What are clinical implications of MHC?
1. Tissue grafting e.g. kidney transplants, skin grafts
2. Certain HLA types are predisposed to certain diseases
3. Forensic medicine
Describe the structure of class I.
Describe the structure of class II.
-two transmembrane polypeptides
what is the main difference between MHC class I and II?
peptide-binding cleft is more open that in MHC Class I
how are peptides anchored into grooves?
formed by upper two domains by hydrogens bonds
What are functions of class I and class II MHC proteins?
-T cells only see antigen in association with MHC proteins
-MHC present antigenic peptides to T cells
-Any one type of MHC molecule can present many peptides with similar structure